Class 11 Biology Revision Notes for Morphology of Flowering Plants of Chapter 5
Morphology is the branch of biological science that deals with the study of form, size, colour, structure and relative position of various parts of organisms. Importance of morphology-
Knowledge of morphology is essential for recognition or identification of plants.
It gives information about the range of variations found in species.
Deficiency and toxicity symptoms are morphological changes that occur in response to shortage or excess of minerals.
Parts of Flowering Plants–
All the flowering plants have roots, stem, leaves, flower and fruits. The underground parts of flowering plant are the root system and the portion above the ground forms the shoot system.
The Root
In Dicotyledons, elongation of radicle forms the primary roots which bears lateral roots of several orders called secondary roots, tertiary roots, etc. Primary roots along with lateral roots forms the Tap root system. Example: Mustard, Gram, etc.
In monocotyledons, primary root is replaced by large number of roots at its base of stem to constitute the Fibrous root system. Wheat, rice etc.
The roots that arise from other parts of plant beside radicle are called adventitious roots. Example- Grass, Banyan tree, Maize, etc.
The main function of root system are absorption of water and minerals from soil, providing proper anchorage to the plant parts and storing reserve food materials.
Regions of Roots–
The apex of root is covered by a thimble like structure called root cap, it protect the tender apex of root while making way through soil.
Above the root cap is region of meristematic activity having small cells with dense cytoplasm.
The part above the region of meristematic activity is region of elongation where cells under go elongation and enlargement to increase the length of root.
Region of maturation contain root hairs that help in absorption of water and minerals.
Modification of roots- Roots are modified for storage, nitrogen fixation, aeration and support.
Tap root of carrot, turnip and adventitious root of sweet potato get swollen to store food.
Prop root of Banyan and Stilt root of maize and sugarcane have supporting root coming out from lower node of stems.
In Rhizophora, Pneumatophores help to get oxygen for respiration as it grows in swampy areas.
The Stem
It is the ascending part of axis bearing branches, leaves, flowers and fruits. It develops from Plumule of the embryo.
Stem bears nodes and internodes. The region of stem where leaves are born are called nodes and portion between two nodes are called internodes.
The main function of stem is spreading branches, bearing leaves, flowers and fruits. It also conducts water and minerals from root to leaves and product of photosynthesis.
Some stem perform special functions like storage of food, support, protection and vegetative propagation.
Modification of stems–
Underground stem of potato, ginger and turmeric are modified to store food. They also act as organ of perennation in unfavorable conditions.
Stem tendril help plants to climb as in cucumber, pumpkins, and grapes.
Axillary buds of stem may modify into woody, straight and pointed thorns as in Citrus and Bougainvillea.
Plants of arid regions modify their stem to flattened (Opuntia), fleshy cylindrical (Euphorbia) having chlorophyll for photosynthesis.
The Leaf
Leaf is a green, dissimilar exogenous lateral flattened outgrowth which is borne on the node of a stem or its branches is specialized to perform photosynthesis.
Leaves originate from shoot apical meristem and are arranged in an acropetal order.
A typical leaf consists of three parts- Leaf base, Petiole, Lamina. Leaf is attached with stem by Leaf Base which may bear two small leaf like structure called stipule.
Middle prominent vein is called mid vein. Veins provide rigidity to the leaf blade and act as channel for transport of water and minerals.
The arrangement of vein and veinlets in the lamina is called venation.
Reticulate venation
Parallel venation
Veinlets form a network.Veins are irregularly distributed.It is present in all Dicotyledons like Gram, Pea, Beans and Mango etc.
A network is absent.Veins are parallel to one another.It is present in Monocotyledons like Grass, Banana, Rice, etc.
A leaf having a single or undivided lamina is called Simple leaf. The incisions do not touch the mid rib. Example- Mango, Guava etc.
When the incision of lamina reach up to the midrib and breaking it into a number of leaflets, it is called Compound leaves.
In a Pinnately compound leaves, a number of leaflets are present on common axis called rachis. Example- Neem.
In Palmately compound leaves, the leaflets are attached at common point. Example- Silk cotton.
The pattern of arrangement of leaves on the stem or branch is called Phyllotaxy.
In alternate type of phyllotaxy single leaf arise at each node as in China rose.
In opposite types of phyllotaxy a pair of leaves arise from each node opposite to each other as in Guava.
If more than two leaves arise at a node and form a whorl is called whorled type of phyllotaxy as in Alstonia.
Leaves are modified to perform other functions like converted to tendril for climbing as in Peas and spines for defence in Cactus.
Inflorescence The arrangement of flowers on the floral axis is termed as inflorescence. Two main types of inflorescence are racemose and cymose.
Racemose
Cymose
The main axis continuous to grow.Flowers are borne laterally in an acropetal succession.Example- Radish, Mustard.
Main axis terminates in flower having limited growth.Flowers are borne in a basipetal succession.Example- Jasmine, Bougainvillea.
The flower
Flower is the reproductive part of angiospermic plants for sexual means of reproduction.
A typical flower has four whorls arranged on a swollen end of stalk or pedicel called thalamus. They are Calyx, Corolla, Androecium and Gynoecium.
When a flower has both androecium and gynoecium, the flower is called bisexual and flower having either androecium or gynoecium only is called unisexual.
When flower can be divided into two equal radial halves in any radii passing through center the symmetry of flower is called actinomorphic (radial symmetry) as in Mustard, Datura, and Chili.
When flower can be divided into two similar parts only in one vertical plane it is zygomorphic as in Pea, Gulmohar, Cassia etc.
When Floral appendages are in multiple of 3,4 or 5 they are called trimerous, tetramerous and pentamerous respectively. Flower with bracts are called bracteates and without it ebracteate.
Based on the position of ovary with respect to other floral part on thalamus, flowers are of following types:
Hypogynous flower– Ovary occupies the highest position. The ovary in such case is called superior. Eg. Mustard, brinjal and china rose.
Perigynous flowers-If the gynoecium is situated at the centre and other parts are on the rim at same height. Ovary is called half-inferior.
Epigynous flowers- The margin of thalamus grows to completely cover the ovary. Ovary is said to be inferior.
Calyx is the outermost whorl of the flower; its members are called sepals. They are generally green and leafy; protect the flower in bud stage. It may be gamosepalous (sepals united) or polysepalous (sepals free). Corolla consists of petals, brightly coloured to attract the insects for pollination. They may be gamopetalous or polypetalous.
The mode of arrangement of sepals or petals in floral bud with respect to the other members of same whorl is called aestivation. In valvate, the whorls of sepals or petals touch each other as in Calotropis. In Twisted aestivation, the whorls overlap each other as in China rose.
In Imbricate aestivation, margin overlap each other but not in particular fashion as in Gulmohur.
In pea and bean flowers, there are five petals- the largest (standard) overlaps the two lateral petals (wings) which in turn overlap two smallest anterior petals (keel). This type of aestivation is known as vexillary or papilionaceous.
The Androecium
Androecium represent the male reproductive parts of flower, consists of stamens. Each stamen consists of filament and anther. Pollen grains are produced in pollen sac. Sterile stamen is called Stemenode.
When stamens are attached with petals it is called epipetalous (Brinjal). Stamen may be free (polyandrous) or may be united in one bundle (monoadelphous), two bundles (diadelphous), more than two (polyadelphous).
The Gynoecium
Female reproductive part of flower consists of one or more carpels. Each carpel is made up of stigma style and ovary.
When more than one carpel is present, it may be free (apocarpous) as in lotus and rose or fused together (syncarpous) as in mustard and tomato.
After fertilisation, ovules change into seeds and ovary mature into fruits.
Placentation
The arrangement of ovules within the ovary is called placentation.
The fruit
Mature and ripened ovary developed after fertilisation is fruit. If a fruit is formed without fertilisation of ovary it is called parthenocarpic fruit.
Fruit consists of seeds and pericarp. Thick and fleshy pericarp is three layered called epicarp, mesocarp and endocarp.
Dicotyledonous Seed is made up of a seed coat and an embryo. Embryo is made up of embryonal axis, radicle and cotyledons.
Seed coat has two layers outer testa and inner tegmen. Hilum is scar through which seed is attached to the ovary. Small pore above the hilum is called micropyle.
Monocotyledonous seeds
In monocotyledonous seed, outer covering of endosperm separate the embryo by a proteinous layer called aleurone layer.
Single cotyledon is called as scutellum having a short axis bearing Plumule and radicle.
Plumule and radicle are closed inside sheaths called as coleoptile and coleorhiza respectively.
SEMI -TECHNICAL DESCRIPTION OF A TYPICAL FLOWERING PLANT The plant is described beginning with its habit, vegetative characters – roots, stem and leaves and then floral characters inflorescence and flower parts. The floral formula is represented by some symbols. In the floral formula, Br stands for bracteate K stands for calyx , C for corolla, P for perianth, A for androecium and G for Gynoecium. Fusion is indicated by enclosing the figure within bracket and adhesion by a line drawn above the symbols of the floral parts. Family Fabaceae-
This family was earlier known as Papilionoideae. Herbs, shrubs or tree root with root nodules. Pinnately compound leaves with reticulate venation.
Economic importance Plants belonging to this family are sources of pulses like Gram, Arhar, Bean. Pea etc. and edible oils like groundnut, soybean, etc. Family Solanaceae-
Plant body herbs or shrubs, rarely small trees, commonly known as potato family. Leaves simple or pinnately compound. Reticulate venation.
Many of them are source of food (potato, tomato, Brinjal etc.), spices (Chilli) etc. Family Liliaceae
Commonly known as Lily family. Monocots, perennial herbs. Leaves alternate with parallel venation.
Underground bulbs, corms or rhizomes.
Flower bisexual, actinomorphic, sepals and petals are absent, having perianth.
It includes ornamental plants (Tulip), Medicine (aloe) and vegetable (colchicine).
Class 11 Biology Revision Notes for Animal Kingdom of Chapter 4
Millions of species of animals have been described and it becomes more necessary to classify them to assign a systematic position.
Animals are classified on the basis of arrangement of cells, body symmetry, nature of coelom, pattern of digestive, circulatory and reproductive system.
Incomplete digestive system has one opening but complete digestive system has two opening- mouth and anus.
Open circulatory system- blood is pumped out of heart and cells and tissue are directly bathed in it.
Closed circulatory system- blood is circulated through arteries, veins and capillaries.
The animals in which cells are arranged in two embryonic layer, external ectoderm and internal endoderm are called diploblastic. Eg. Porifera and Cnidaria.
The animals in which developing embryo has a third germinal layer, mesoderm besides ectoderm and endoderm are called triploblastic. Eg. Platyhelminthes, Chordates.
The body cavity which is lined by mesoderm is called coelom. Animals possessing coelom are called coelomate (Annelida, Chordates, Mollusca). In some animals cavity is not lined by mesoderm but scattered as pouches in between ectoderm and endoderm, are called pseudo-coelomates (Aschelminthes). The animals in which body cavity is absent are called acoelomate (Platyhelminthes).
In some animals, body is externally and internally divided into segments with serial repetition as in earthworm, called metameric segmentation.
CLASSIFICATION OF ANIMALS Phylum Porifera-
Members of this phylum are commonly known as sponges. Mostly marine, asymmetrical and have cellular level of organization.
They have water transport or canal system. Water enters through minute pores, Ostia into central cavity Spongocoel, from where it goes out through Osculum.
Nutrition, respiration and excretion is performed by pathway of water transport system.
Skeleton made up of spicules or spongin fibres.
Egg and sperms are produced by same organism (hermaphrodite). Asexual reproduction by fragmentation and sexual reproduction by gametes formation.
Fertilisation internal and development is indirect.
Example– Sycon, Spongilla.
Phylum Cnidaria ( Coelenterate)-
They are aquatic, mostly marine, sessile, free swimming, radially symmetrical animals.
They exhibit tissue level of organization, diploblastic, coelomate with single opening.
They show two types of body called polyp and medusa.
Polyp is sessile, fixed, and cylindrical, without gonads. Example: Hydra, Adamsia. Medusa is free swimming, umbrella like having gonads like Aurelia and Jelly fish.
Some cnidarians exhibits both forms (Obelia). Polyp produce medusa asexually and medusa produce polyp sexually.
Phylum Ctenophora-
Commonly known as the Comb Jellies or Sea Walnuts.
Exclusively marine, diploblastic, radially symmetrical, with tissue level of organization.
Body bears eight ciliated comb plates which help in locomotion.
Bioluminescence (to emit light) is present in Ctenophores.
Are Hermaphrodite, fertilisation is external, development indirect.
Example- Ctenoplana, Pleurobranchia.
Phylum Platyhelminthes (The Flat worms)
Dorso-ventrally flattened body, bilaterally symmetrical, triploblastic, acoelomate with organs levels of organization.
Hooks and sucker are present in parasitic forms. Flame cells help in osmoregulation and excretion.
Fertilisation is internal, development is indirect. They are hermaphrodite.
Example- Taenia, Planaria, Fasciola.
Phylum Aschelminthes (The Round Worm)
They may be free-living, aquatic, terrestrial or parasitic in plants or animals.
Largest phylum of animals which includes insects. They have organ system of organization. They are triploblastic, coelomate, bilaterally symmetrical with chitinous exoskeleton.
Body consists of head, thorax and abdomen, jointed appendages (jointed feet). Respiratory organs are gills, book lungs or tracheal system with open circulatory system.
Excretion through malpighian tubules, sense organs antenna or eyes. Fertilisation internal, mostly oviparous.
Class 11 Biology Revision Notes for Plant Kingdom of Chapter 3
Eukaryotic, multicellular, chlorophyll containing and having cell wall, are grouped under the kingdom Plantae. It is popularly known as plant kingdom.
Phylogenetic system of classification based on evolutionary relationship is presently used for classifying plants.
Numerical Taxonomy use computer by assigning code for each character and analyzing the features.
Cytotaxonomy is based on cytological information like chromosome number, structure and behaviour.
Chemotaxonomy uses chemical constituents of plants to resolve the confusion.
Algae: These include the simplest plants which possess undifferentiated or thallus like forms, reproductive organs single celled called gametangia. It includes only Algae. Characteristic of Algae
Plant body is thallus, which may be unicellular, colonial, filamentous or parenchymatous.
Usually aquatic but a few are also found in moist terrestrial habitats like tree trunks, wet rocks, moist soil, etc.
Vascular tissues and mechanical tissues are absent.
Reproduction is vegetative by fragmentation, asexual by spore formation (zoospores) and sexual reproduction by fusion of two gametes which may be Isogamous (Spirogyra), Anisogamous (Chlamydomonous) or Oogamous (Volvox).
Life cycle is various- haplontic, diplontic or diplohaplontic.
Green Algae
Brown Algae
Red Algae
Mostly fresh water and sub aerial.
Mostly marine.
Mostly marine.
Unicellular organisms abundant.
Unicellular species are absent.
Unicellular species fewer.
Chlorophyll a and b type.
Chlorophyll a and c type.
Chlorophyll a and d type.
Reserve food is starch
Reserve food is laminarin.
Reserve food is floridean starch.
Cell wall is of cellulose.
Cell wall contains cellulose and algin.
Cell wall contains cellulose and poly-sulphate esters.
Fucoxanthin is absent
Fucoxanthin present.
Phycoerythrine is present.
Zoospores present.
Zoospores present.
Zoospores absent.
Chlamydomonas, Ulothrix, spirogyra.
Focus, Sargassum, ectocarpus.
Polysiphonia, Gelidium, Porphyra etc.
Economic importance-
A number of brown algae ( Laminaria, Sargassum) are used as food in some countries.
Fucus and Laminaria are rich source of Iodine.
Laminaria and Ascophyllum have antibiotic properties.
Alginic acid is obtained from Fucus and Sargassum, which is used as emulsions.
Bryophytes – They are non-vascular mosses and liverworts that grow in moist shady region. They are called amphibians of plants kingdom because these plants live on soil but dependent on water for sexual reproduction. Characteristic features-
Live in damp and shady habitats, found to grow during rainy season on damp soil, rocks, walls, etc.
The dominant phase or plant body is free living gametophyte.
Roots are absent but contain rhizoids
Vegetative reproduction is by fragmentation, tubers, gemmae, buds etc. sex organs are multicellular and jacketed. The male sex organ is called antheridium. They produce biflagellate antherozoids. The female sex organ called archegonium is flask-shaped and produces a single egg.
Sporophyte is dependent on gametophyte for nourishment.
Bryophytes Hepaticopsida (Liverworts)
The plant body of a liverwort is thalloid, e.g., Marchantia. The thallus is dorsiventral and closely appressed to the substrate.
Asexual reproduction in liverworts takes place by fragmentation, or by the formation of specialised structures called gemmae.
Gemmae are green, multicellular, asexual buds, which develops in small receptacles called gemma cups. The gemmae becomes detached from the parent body and germinate to form new individuals
During sexual reproduction, male and female sex organs are produced either on the same or on different thalli. The sporophyte is differentiated into a foot, seta and capsule. Spores produced within the capsule germinate to form free-living gametophytes.
Bryopsida (Mosses)
The gametophyte of mosses consists of two stages- the first stage is protonema stage, which develops directly from spores. It is creeping, green and frequently filamentous. The second stage is the leafy stage, which develops from secondary protonema as lateral bud having upright, slender axes bearing spirally arranged leaves.
Vegetative reproduction is by the fragmentation and budding in secondary protonema. In sexual reproduction, the sex organs antheridia and archegonia are produced at the apex of the leafy shoots.
Sporophytes in mosses are more developed and consist of foot, seta and capsule.
Common examples are Funaria, Polytrichum, Sphagnum etc.
Pteridophytes
They are seedless vascular plants that have sporophytic plant body and inconspicuous gametophyte. Sporophytic plant body is differentiated into true stem, roots and leaves.
Vascular tissue are present but vessels are absent from xylem and companion cells and sieve tube are absent.
Sporophytes bear sporangia that are subtend by leaf like appendages called sporophylls. In some plants (Selaginella) compact structure called strobili or cone is formed.
Sporangia produce spores by meiosis in spore mother cells. Spores germinate to produce multicellular thalloid, prothallus.
Gametophyte bears male and female sex organ called antheridia and archegonia. Water is required for fertilisation of male and female gametes.
Most of Pteridophytes produce spores of similar kind (homosporous) but in Selginella and Salvinia, spores are of two kinds (heterosporous) larger called megaspore that produce female gametophyte and smaller microspore that produce male gametes.
Gymnosperms:
Gymnosperms are those plants in which the ovules are not enclosed inside the ovary wall and remain exposed before and after fertilisation.
They are perennial and woody, forming either bushes or trees. Some are very large (Sequoia sempervirens) and others are very small (Zamia pygmia).
Stem may be unbranched(Cycas) or branched(Pinus). Root is taproot. Leaves may be simple or compound.
They are heterosporous, produce haploid microspore and megaspore in male and female Strobili respectively.
Male and female gametophytes do not have independent free-living existence. Pollination occurs through air and zygote develops into embryo and ovules into seeds. These seeds are naked.
Example- Pines, Cycus, Cedrus, Ginkgo, etc.
Angiosperms
Pollen grain and ovules are developed in specialized structure called flower. Seeds are enclosed inside the fruits.
Size varies from almost microscopic Wolfia (0.1cm)to tall tree Eucalyptus (more than 100m
The male sex organs in a flower is the stamen. It contains pollen grain.
The female sex organs in a flower is the pistil or the carpel. Pistil consists of an ovary enclosing one or many ovules. Within ovules are present highly reduced female gametophytes termed embryo-sacs.
Each embryo-sac has a three-celled egg apparatus – one egg cell and two synergids, three antipodal cells and two polar nuclei. The polar nuclei eventually fuse to produce a diploid secondary nucleus.
Angiosperms are further classified into:
Monocotyledons
Dicotyledons
Monocotyledons
Dicotyledons
Single cotyledons.Parallel venation.Fibrous root system.Closed vascular bundle.More number of vascular bundles.Banana, wheat, rice.
Two cotyledons.Reticulate venation.Tap root system.Open vascular bundle.Less number of vascular bundles.Gram, mango, apple.
Double fertilisation- Each pollen grain produce two male gametes. One gametes fuse with egg to form embryo. This is called Syngamy. Other gametes fuse with two polar nuclei to form endosperm, triple fusion. Since fertilisation takes place twice, it is called double fertilisation.
Alternation of generation Different plant groups complete their life cycles in different patterns. Angiosperms complete their life cycle in two phases- a diploid sporophytes and haploid gametophyte. The two follows each other. This phenomenon is called alternation of generation.
Haplontic- Saprophytic generation is represented by only the one-celled zygote. Meiosis in zygote results into haploid spores to form gametophytes, which is the dominant vegetative phase. Example- Volvox, Spirogyra etc.
Diplontic- Diploid sporophytes is dominant, independent, photosynthetic plants. The gametophyte is represented by single to few celled. All seed bearing plants fall under this category.
Haplo-diplontic- Both phases are multicellular and intermediate condition is present. It is present in Bryophytes and Pteridophytes.
Revision Notes for Class 11 Biology Chapter 2 – Biological Classification
Biological classification is the scientific procedure of arranging organisms into groups and subgroups on the basis of their similarities and dissimilarities and placing the group in a hierarchy of categories. Importance of classification-
It is not possible to study every organism. Study of one or two organism of a group gives sufficient information about the essential features of the group.
It helps in identification of new organism.
Classification helps in knowing the relationship amongst different groups of organisms.
The organism of past cannot be studied without a proper system of classification.
Classification
Artificial system of classification
Natural system of classification
Phylogenetic system of classification
Artificial system of classification– Only one or two morphological characters for grouping of organism is used. Flowering and non-flowering plants, enaima and anaima. Aristotle classification. Natural system of classification– Takes into consideration comparable study of a number of characters so as to bring out natural similarities and dissimilarities and hence natural relationships among the organisms. Bentham and Hooker classification, etc. Phylogenetic System of Classification– Based on the evolutionary relationship of organisms. In this system organism are classified on the basis of their evolution on earth from primitive to highly evolved. Engler and Prantl classification and Hutchinson classification, etc.
Two kingdom : Plantae Animalia
Three kingdom : Plantae Protista Animalia
Five kingdom : Monera Protista Fungi Plantae Animaila
In two kingdom system of classification organisms are grouped on the basis of presence and absence of cell wall as proposed by Linnaeus( father of taxonomy).
Three kingdom systems- Haeckel separated unicellular animals, algae and fungi on the basis of lack of tissue differentiation and new kingdom Protista was introduced.
Five kingdom systems- R.H.Whittaker divided all the organism into five kingdom in order to develop phylogenetic classification.
Monera– The kingdom includes all prokaryotes- mycoplasma, bacteria, actinomycetes and cyanobacteria.
Unicellular, prokaryotes and contain the most primitive of living forms
The cells are microscopic and cell wall is generally present.
Genetic materials are not organized into nucleus and contain naked DNA.
Membrane bounded organelles are absent.
Reproduction is asexual except gene recombination.
Flagella may be present and are of single stranded.
Example- Blue-green algae, Bacteria, etc. Bacteria are the most abundant micro-organism that can survive in all kinds of climate.
They are group of most primitive prokaryotes which live under most hostile conditions like extreme salty area (halophiles), hot springs (thermoacidophiles) and marshy area (methanogens). They differ from other bacteria in having different cell wall structure (absence of peptidoglycan). Methanogens are present in the gut of several ruminant animals like cows and buffalo, which is responsible for production of biogas (methane) from dung of these animals.
Eubacteria – They are called as true bacteria. They contain rigid cell wall, if motile contain flagellum. Cyanobacteria or blue-green algae are gram positive photosynthetic bacteria. They contain chlorophyll a and carotenoids. They may be unicellular, colonial or filamentous, fresh water, marine or terrestrial. Some of them have specialized heterocyst cells to perform nitrogen fixation (Nostoc and Anabaena). Chemosynthetic bacteria oxidize inorganic substances like nitrate, nitrite, ammonia etc. to produce energy and help in recycling of nitrogen, phosphorous, sulphur etc. Heterotrophic bacteria are most abundant and act as decomposer. They are helpful in production of curd, antibiotic and fixing nitrogen in leguminous plants. Some of them are pathogenic and cause disease like cholera, typhoid, tetanus and citrus canker. Mycoplasma – they are the simplest free living prokaryotes. They are also known as PPLO (Pleuropneumonia like organism). They lack cell wall and can survive without oxygen. They cause disease in plants and animals. Protista– Kingdom Protista includes Chrysophytes, Dinoflagellates, Eugleoids, slime mould and Protozoans.
It includes all unicellular and colonial eukaryotes.
Most of them are aquatic forming plankton.
Mode of nutrition may be photosynthetic, saprophytic, parasitic or holozoic.
Flagella if present are 11 stranded with 9+2 arrangement of microtubules composed of tubulin.
Genetic material consists of 2 or more DNA molecules.
They includes diatoms and golden algae (desmids) found in fresh water as well as marine water.
In diatoms cell wall forms two thin overlapping cells which fit together as in soap box.
The siliceous indestructible cell wall pile up at the bottom of water reservoirs and form big heaps called diatomaceous earth. It may extend for hundred meter and used for polishing, filtration of oil and syrups. They are chief producer in oceans.
They are basically unicellular, motile, biflagellate and photosynthetic protists.
Predominate colour is golden brown but yellow, green, red and even blue also exists.
Some Dinoflagellates like Gymnodinium and Gonyaulax grow in large number in the sea and make the water look red and cause the so called “red tide”.
They are Euglena like unicellular flagellates which possess pellicle instead of cell wall which make their body flexible.
They have two flagella, one short and other long.
They are photosynthetic in presence of sunlight and act as predators in absence of sunlight.
Example- Euglena, Peranema.
Slime Moulds
They are saprophytic protists and feeds on decaying twigs and leaves.
Under favorable condition, they form an aggregation called plasmodium which produce fruiting bodies bearing spores.
The cell wall of spores contain cellulose.
The spores are dispersed by air currents.
Example- Physarum, Fuligo.
Protozoans
All protozoans are heterotrophs and live as predators or parasites.
They are considered as primitive relatives of animals.
Amoeboids move and capture food by pseudopodia. Some are parasitic also.
Flagellated protozoans are free-living or parasitic. They have flagella.
Ciliated protozoans are aquatic and have cilia all over the body for movement.
Sporozoans includes organism that have infectious spore like stage in their life cycle.
Kingdom Fungi–
They are achlorophyllous, heterotrophic, spore forming, non-vesicular eukaryotic organisms.
Cell wall is made up of chitin or fungal cellulose.
Reserved food is glycogen.
Mode of nutrition is saprophytic, parasitic or symbiotic.
Reproduction may be vegetative (fragmentation, fission or budding), asexual (conidia, sporangiospores or zoospores) or sexual reproduction by oospores, ascospore and basidiospores.
Sexual cycles involves the following steps-
Plasmogamy, fusion of male and female gametes.
Karyogamy, fusion of two nuclei.
Meiosis in zygote to produce haploid spores.
Phycomycetes–
They are found in aquatic habitat and on decaying wood in moist and damp places.
The mycelium is aseptate and coenocytic.
Asexual reproduction by zoospores( motile) or aplanospores (non-motile).
Example- Mucus, Rhizopus, Albugo etc.
Ascomycetes (The sac fungi)
They are saprophytic, decomposers, parasitic or coprophilous (growing on dung).
Mycelium and branched and septate and asexual spores are conidia.
Sexual spores are called ascospores produced inside the fruiting body called ascocarps.
Example- Neurospora, Asperigillus, Claviceps etc. Basidiomycetes (The club fungi)
The mycelium is branched and septate.
Vegetative reproduction is by fragmentation. Asexual spores are not found. Sexual reproduction is by two vegetative or somatic cells forming basidium.
Basidiospores are produced in basidium by developing a fruiting body called basidiocarps.
Example- Agaricus, Ustilago, Puccinia.
Deuteromycetes (The fungi imperfect)
Only vegetative and asexual phase is known.
Mycelium is septate and branched. Some members are saprophytes or parsites.
Example- Alternaria, Trichoderma, Colletotrichu.
Kingdom Plantae
Eukaryotic, chlorophyll bearing organism.
Life cycle is divided into diploid saprophytic and haploid gametophytic, which alternate with each other.
Kingdom Plantae includes Algae, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms.
Kingdom Animalia
Heterotrophic, eukaryotic organisms that are multicellular and cell wall is absent in the cell.
Mode of nutrition is holozoic and reserve food is glycogen or fats.
Sexual reproduction is by copulation between male and female followed by embryological development.
Virus, Viroids and Lichens Five kingdom system of classification do not includes Virus, Viroids and Lichens.
Viruses are non-cellular organisms having inert crystalline structure outside the living. When they enter the living cell, they take over the machinery of living cell to replicate themselves.
D.J.Ivanowsky recognized certain microbes as causal organism of mosaic disease of tobacco.
In addition to proteins, viruses also contain genetic material that could be DNA or RNA. In general, virus that infect plants have single stranded RNA and virus that infect animals have double stranded DNA.
Some common diseases caused by virus are common cold, influenza, AIDS, small pox, leaf rolling and curling.
Bacteria feeding virus are called Bacteriophage.They are usually double stranded DNA viruses.
The protein coat called capsid is made of small subunits called capsomeres, protects the nucleic acid. These capsomeres are arranged in helical or polyhedral geometric forms.
Viroids are discovered by T.O.Diener as new infectious agent smaller than virus causing potato spindle tuber disease. They are free RNA without protein coat.
Lichens are symbiotic association between algae and fungi. The algal part is called Phycobiont and fungal parts are called Mycobiont. They are good pollution indicator as they do not grow in polluted area.
Non-living things like mountains, boulders, sand dunes also grow in size, but just by accumulating the material on their external surface. Thus, growth in living things is internal, while in non-living things, it is external. It is to be noted that a dead organism do not grow.
2. Reproduction Reproduction, a characteristic of living organisms is the process of producing offsprings, possessing features similar to those of parents. In multicellular organisms, the mode of reproduction is generally sexual. Living organisms also reproduce by asexual means. Some examples are given below (i) Fungi spread and multiply fast by producing millions of asexual spores. Some fungi, the filamentous algae and the protonema of mosses multiply by fragmentation. (ii) In yeast and Hydra, budding occurs to produce new organisms. While, in Planaria (flatworm), regeneration of fragmented body parts occur. These parts inturn grow as a new organism. (iii) Unicellular organisms like bacteria, algae and Amoeba reproduce by increasing the number of cells, i.e., through cell division (growth is synonymous with reproduction). Some organisms like mules, sterile worker bees, infertile human couples, etc., do not reproduce. Hence, reproduction also cannot be an all-inclusive defining characteristic of living organisms.
3. Metabolism Metabolism is an another characteristic and defining feature of all living things. The sum total of anabolic or constructive reactions (anabolism) and catabolic or destructive reactions (catabolism) continuously occurring inside the body is called metabolism. Metabolism —> Anabolism + Catabolism Metabolism occurs in all unicellular and multi cellular organisms. Its two stages include, i.e., anabolism, the process of building up or synthesis of complex substances from simpler ones, e.g., Photo synthesis and catabolism, the process of breakdown of complex substances into simpler substances, e.g., Respiration, releasing waste outside. Metabolic reactions can also be demonstrated outside the body in cell free systems, which are neither living nor non-living. Thus, these reactions in vitro are surely living reactions not living things. Hence, metabolism can be considered as a defining feature of all living organisms without exception. The important differences between anabolism and catabolism are
Viruses are considered as non-living because they don’t need energy for their activities, i.e., metabolic activities are altogether absent in them.
4. Cellular Organisation The cells are the building blocks of all living things whether plants, animals or humans. The unicellular organisms are made of a single cell, while multi cellular organisms are formed by millions of cells. The cells contain protoplasm (living matter) and cell organelles (inside the cells) which perform several activities at the cellular level and result into various life processes.
5. Consciousness All living organisms have excellent ability to sense their environment. They respond to various physical, chemical and biological stimuli. The various external factors to which living organisms respond are light, water, temperature, pollutants, other organisms, etc. Light duration or photo period affects many seasonal breeders, plants as well as animals. All living things respond to chemicals, entering their * bodies. Humans are superior to all living things as they have an additional ability of self-consciousness. Therefore, consciousness can also said to be a defining property of living organisms. However, in human beings, it is more difficult to define living state, e.g., Patients lying in coma supported by machines that replace heart and lungs, are brain-dead with no self-consciousness.
6. Body Organisation The body of living organisms is organised, i.e., several component and sub-components cooperate with each other for the functioning of whole body.
Physical and Biological Hierarchies There is a physical (non-living) hierarchy and biological hierarchy in the organisation of living body. In physical hierarchy, various non-living components aggregate to form compounds, which finally enter the living world in the form of cells. These cells organise to form tissues, that form organs and several organs combustive to form organ-systems. Finally, many organ systems organise and form a living organism.
The properties of tissues are not present in the constituent cells but arise as a result of interactions among the constituent cells. For example, bone is a hard tissue, which provides framework to the body. But, the cells present inside it do not have this property. This phenomenon of interactions between various components of the body results in the hierarchy of organisation.
The various life processes are the result of this interaction and coordination. The complexity in organisation enable living organisms as to be self-replicating, evolving, self-regulating and responding to external stimuli. All living organisms along with their ancestors and descendants are linked to one another by sharing of common genetic material in the form of DNA in varying degrees. This DNA is responsible for the expression of specific traits in organisms. Thus, Biology is the story of life on earth. It is the story of evolution of living organisms on the earth.
Some Other Characteristics of Living Organisms We have discussed some important and defining characteristics of living things. However, organisms . also have many other features that differentiate them from non-living things, such as, shape & size, life cycle, movement, self-regulation, variations, adaptations, healing & repair, excretion and death.
2. Living World : Diversity and Taxonomy
The earth hosts an immense variety of living organisms. According to a survey, the number of species that are known and described are between 1.7-1.8 million. This number refers to the biodiversity on the earth. The term Biodiversity or Biological diversity means the number and types of organisms present on the earth, forms of life in the living world. The living world includes all the living organisms, such as microorganisms, plants, animals and humans. Biodiversity is not limited to the existing life forms. If we explore new areas and even old ones, new organisms are continuously being added. This huge available variety cannot be studied and identified without having a proper system of classification and nomenclature.
Systematics The word ‘Systematics’ is derived from the Latin word Systema, which means systematic arrangement of organisms. Linnaeus used Systema Naturae as the title of his book. He. coined the term Systematics in 1751. Systematics is the branch of science that deals with unique properties of species and groups to recognise, describe, name and arrange the diverse organisms according to an organised plan. In 1961, Simpson, defined systematics as the study of diversity of organisms and all their comparative and evolutionary relationships based on comparative’ anatomy, physiology, biochemistry and ecology. The word ‘Systematics’ and ‘Taxonomy’ are often used interchangeably by the biologists. Systematics includes the following:
Identification It aims at finding the correct name and appropriate position of an organism. The morphological and anatomical characters are examined for proper identification.
Classification It is almost impossible to study all the living organisms. So, it is necessary to devise some means to make this possible. This can be done by classifying the organisms. Thus, classification is the process by which organisms are grouped into categories based on some easily observable characters. Biological classification is the scientific arrangement of organisms in a hierarchy of groups and sub-groups on the basis of similarities and differences in their traits.
Advantages of Classification (a) It helps to identify an organism easily. (b) New organisms easily get correct place in their respective groups. (c) It makes study of fossils easy. (d) It also helps in building evolutionary pathways. (e) It becomes easy to know the features of whole group by studying one or two organisms of the group. Thus, based on these characteristics, all living organisms are classified into different taxa.
Nomenclature
Nomenclature is the system of naming living organism in a way that a particular organism is known by the same name all over the world. i. Common Names The common names or vernacular names are the local names given to an organism in a specific language in a particular region. There are different names of a same organism in different regions even with in a country.
Advantages of Common Names (a) Common names are easy to pronounce and are short, e.g., Cat or billi. (b) People are familiar to these names since childhood. (c) They are based on some features of organisms, e.g., Cowa (crow—Caawn-Caawn sound).
Dis-Advantages of Common Names (a) All the organisms cannot be named by this method as there are organism of different sizes and shapes. e.g., Microbes. (b) An organism may have several names in a given language, e.g., 8 Hindi names of prickly poppy and water lily has 15 English names. (c) A common names may have different meanings in different countries, e.g., Maize, means wheat and other grains in USA and it is called corn in common wealth countries. (d) Common names may have little relevance, e.g., Lady’s finger (okra), widows tears (Tradescantia-Rhoeo), etc. (e) Common names may be incorrect, e.g., Jelly fish (a coelenterate), silverfish (an arthropod), starfish (an echinoderm) are not real fishes. (f) These names are not useful for scientific studies.
ii. Scientific Names A scientific name is given by biologists. These names represent a particular organism in every part of the world. The system of providing scientific names is called binomial nomenclature. The scientific names must be (a) acceptable in every part of the world. (b) assigned on agreed principles and criteria. (c) different for each species and not used for other organisms earlier.
Binomial Nomenclature Binomial nomenclature was developed by Carolus Linnaeus in 1751 (Philosphica Botanica). All scientific names for animals under binomial nomenclature were given by Linnaeus in the tenth edition of his book Systerna Naturae (1758). Linnaeus named plants according to binomial nomenclature in his book Species Plantarum (1753). Binomial nomenclature is the system of providing distinct and appropriate names to organisms, each consisting of two words, first generic name {i.e., name of genus) and second specific epithet (i.e., name of species). For example, Scientific name of mango is written as Mangifera indica. In this name, Mangifera represents the genus and indica is a particular species or specific epithet.
Rules of Binomial Nomenclature Rules of binomial nomenclature were initially framed by Linnaeus in his books, Species Plantarum and Systema Naturae.
The rules were revised again by the following nomenclature codes (i) International Code for Botanical Nomenclature (ICBN). (ii) International Code of Zoological Nomenclature (ICZN). (iii) International Code of Bacteriological Nomenclature (ICBN). (iv) International Code of Viral Nomenclature (ICVN). (v) International Code of Nomenclature for Cultivated Plants (ICNCP).
The rules framed by Linnaeus and by these codes are as follows (i) The names are generally in Latin and written in italics. They are Latinised or derived from Latin irrespective of their origin. (ii) The first word in a biological name represent the genus while, the second component denotes the specific epithet. (iii) Both the words in a biological name, when handwritten are separately underlined or printed in italics to indicate their Latin origin. (iv) The first word denoting the genus starts with capital letter while, the specific epithet starts with a small letter, e.g., Mangifera indica. (v) Generic and common names may be same, e.g., Gorilla gorilla. (vi) No names are recognised prior to those used by Linnaeus in 1753 for plants in Species Plantarum and in 1758 for animals in the 10th edition of Systema Naturae. (vii) The name of categories higher than the rank of genus are not printed in italics. Bold letters can, however be used. (viii) When a species is transferred or revised, the name of the original worker is retained but in parenthesis, e.g., Syzygium cumini (L) Skeels.
Advantages of Binomial Nomenclature (i) Binomial names are universally acceptable and recognised. (ii) They remain same in all languages. (iii) The names are small and comprehensive. (iv) There is a mechanism to provide a scientific name to every newly discovered organism. (v) The names indicate relationship of a species with other species present in the same genus. (vi) A new organism can be easily provided with a new scientific name.
Taxonomy
It is the science of identification, classification and nomenclature. Based on their special / characteristics, all living organisms can be classified into different taxa. This process of classification is called taxonomy. Carolus Linnaeus is known as father of taxonomy. The basis of modern taxonomy studies are external and internal structure (comparative morphology), along with the structure of cells (cytology), development process (embryology) and ecological information of organisms (ecology). It provide information according to similarities, dissimilarities and evolutionary relationships of various organisms.
The basic processes for taxonomic studies are (i) Organisms are described on the basis of morphology and other characteristics. (ii) The description of characteristics helps in the placement of the organism in various taxa. (iii) A new taxon can be framed if the organism is different from the existing taxa. (iv) The correct naming of an organism can be done after placing it in various taxon. A new organism can be given a new name after following the standardized rules.
Classical Taxonomy (Old Taxonomy) The concept of classical or old taxonomy exists since, the time of Aristotle and Theophrastus and continued up to Linnaeus. It states that 4 . (i) Species is the basic unit of taxonomy, that can be described on the basis of one or few preserved specimens. (ii) Species are fixed and do not change with time. (iii) A species is delimited based on morphological features. (iv) Organisms are classified on the basis of some limited features such as root modification, leaf venation, floral structures, number of cotyledons in case of plants. Due to the limited number of groups, many organisms could not be classified correctly. This finally led to artificial system of classification.
Modern Taxonomy (New Taxonomy) The concept of modern taxonomy was given by Julian Huxley (1940). It uses evidences from all the areas of biology like morphology, anatomy, biochemistry, cell biology, physiology, genetics, evolution, etc. The modem taxonomy is based on the following features (i) The studies are done on a huge number of organisms based on all the variations. (ii) Study is also focused on sub-species, varieties, races and populations. (iii) Species are not isolated. They are related by common descent and vary from them due to accumulation of variations. (iv) Species is considered as dynamic and ever-changing entity. (v) Biological delimitation includes various branches of systematics, e.g., Cytotaxonomy, experimental taxonomy, numerical taxonomy, chemotaxonomy, etc. This led to the development of phylogenetic system or cladistics of classification. Taxonomic Categories Classification is not a single step process. It involves hierarchy of steps in which each step represents a rank or category. Since, the category is a part of overall taxonomic arrangement, it is called the taxonomic category and all categories together constitute the taxonomic hierarchy.
Taxon Each category, referred to as a unit of classification, in fact, represents a rank and is commonly termed as taxon (Pi. taxa). The term Taxon was first introduced by ICBN during 1956. According to Mayr (1964) taxon is a group of any rank that is sufficiently distinct to be worthy of being assigned a definite category. In simple words, taxon refers to a group of similar, genetically related individuals having certain characters distinct from those of other groups. A taxon that includes a common ancestral species and all the species descended from it is called a clade or a monophyletic taxon.
Taxonomic Hierarchy
The taxonomic hierarchy is the system of arranging taxonomic categories in a descending order. It was first introduced by Linnaeus (1751) and hence, it is also known as Linnaen hierarchy. Groups represent category and category further denotes rank. Each rank or taxon represents a unit of classification. These taxonomic groups/categories are distinct biological entities and not merely morphological aggregates.
Obligate/Common Categories The taxonomic categories, which are always used in hierarchical classification of organisms are called obligate or common categories. They are seven in number. In descending order, these are kingdom, phylum or division, class, order, family, genus and species. All the members of taxonomic categories possess some similar characters, which are different from those of others. The maximum similarity occurs in species, which is also the lowest category in the hierarchy of categories. Similarity of characters decreases with the rise in hierarchy.
i. Species Taxonomic studies consider a group of individual organisms with fundamental similarities as a species (John Ray).
Species is considered as the lowest or basic taxonomic category, which consists of one or more individuals of a populations that resemble one another more closely than individuals of other species. The members of species interbreed freely and are reproductively isolated from others. For example, Mangifera indica (mango), Solarium tuberosum (potato) and Panthera leo (lion).
All the three names indica, tuberosum and leo represent the specific epithets while, the first words Mangifera, Solanum and Panthera are genera and represents another higher level of taxon or category. Each genus may have one or more than one specific epithets representing different organisms, but having morphological similarities. For example, Panthera has another specific epithet called tigris and Solanum includes species like nigrum and melongena.
ii. Genus Genus (John Ray) comprises a group of related species, which has more characters common in comparison to species of other genera. In other words, genera are aggregates of closely related species.
iii. Family Family (John Ray) is a group of related genera with less number of similarities as compared to genus and species. All the genera of a family have some common or correlated features. They are separable from genera of a related family by important differences in both vegetative and reproductive features. A plant family ends in a suffix -aeae and sub-family -oideae. While, an animal family has a suffix -idae and sub-family -inae.
iv. Order An order (Linnaeus) is a group of one or more related families that possess some similar correlated characters, which are lesser in number as compared to a family or genera. Plants and Animal Orders with their Respective Families Order Animals and Families Carnivora Canidae (dog, wolf and fox), Felidae (cat, leopard, tiger and lion), Ursidae (bear) and Hyaenidae (hyaena) Polemoniales Solanaceae (potato and tomato), Convolvucaceae (sweet potato and morning glory), Polemoniaceae (herbs, shrubs and small trees) and Hydrophyllaceae (water leaf). Primates Lemuridae (lemurs), Cebidae (new world monkeys), Pongidae (apes) and Hominidae (humans).
v. Class Class (Linnaeus) is a major category, which includes related orders. For example, order-Primata comprises monkey, gorilla & gibbon and is placed in class—Mammalia along with order—Carnivora that includes animals like tiger, cat and dog. Class-Mammalia has other orders also.
vi. Phylum or Division Phylum or Division (Cuvier, Eichler) is a taxonomic category higher than class and lower” in rank to kingdom. The term Phylum is used for animals, while division is commonly employed for plants. It consists of more than one class having some similar corelated characters. For example, Phylum— Chordata of animals contain following classes, e.g., Pisces, amphibians, reptiles, aves and mammals.
vii. Kingdom It is known to be the highest category in taxonomy. This includes all the organisms, which share a set of distinguished characters. For example, all the animals belonging to various phyla are assigned the highest category called kingdom. For example, Animalia in the classification system of animals. Similarly, all the plants are kept in kingdom—Plantae. RH Whittaker. (1969) assigned five kingdom classification of organisms. These are Monera, Protista, Fungi, Plantae and Animalia.
Intermediate Categories The taxonomic categories from species to kingdom are broad categories or obligate categories. However, taxonomists have also developed sub-categories in this hierarchy to facilitate more sound and scientific placement of various taxa. These sub-categories are sub-species (or varieties), sub-genera, sub-families, sub-orders, sub-classes and sub-phyla. These sub-categories are referred to as intermediate categories.
Taxonomical Aids
Taxonomical aids are techniques and procedures to store information as well as specimens or identification and classification of organisms.
The taxonomic studies of various plants, animals and other organisms are useful in areas like agriculture, forestry, industry and knowing our bioresources. All these studies need correct identification and classification of organisms. Identification of organisms requires intensive laboratory and field studies. The collection of actual specimens of plants and animal species, knowing their habitats and other traits are essential and are the prime source of taxonomic studies. All this information is used in classification of an organism and is also stored along with the specimens. Sometimes, specimens are also preserved for future studies. Some of the taxonomical aids developed by Biologists include Herbarium, Botanical gardens, Museum, Zoological parks, Key, etc.
1. Herbarium Herbarium (Pi. Herbaria) is a store house of collected plant specimens that are dried, pressed and preserved on sheets. These sheets are arranged further according to a universally accepted system of classification. The institutes and universities maintain their own herbarium by collecting specimens from local and far away places.
Uses of Herbaria The uses of herbaria are listed below (a) These are used for identification of plants. (b) Compilation of floras, monographs and manuals are mainly based on the specimens in herbaria. (c) Herbaria are useful in locating wild varieties and relatives of economically important plants. (d) They help in knowing the morphological variations found in species. (e) Herbaria are useful for research in plant taxonomy, morphology, ecological distribution, etc.
2. Botanical Gardens Botanical gardens are specialised gardens that have collections of living plants for reference. These gardens generally have facilities like library, laboratory, herbarium and museum. The botanical gardens are maintained by government, semi-government and other private organisations. Botanists and gardeners look after plants in botanical gardens.
Role of Botanical Gardens A botanical garden has following important roles (a) Botanical gardens have aesthetic appeal and provide recreation facility to people. (b) A wide variety of plant species grow there, so they provide ready material for research. (c) These gardens also play an important role in conservation of endangered plant species and genetic diversity. (d) There are more than 500 botanical gardens all over the world. These provide free exchange of seeds. (e) These improve the environment, provide greenery, help in creating pollution free environment and some serves as habitat for animals. Knowledge Plus Indian Botanical Garden-Largest Botanical Garden of Asia. First Botanical Garden-Pisa Botanical Garden, Italy established by Luca Glini (1490-1556).
3. Museums Museum is a place for collections of preserved plants and animal specimens for study and reference. The universities and educational institutes maintain their own museums in their botany and zoology departments. Plants, which cannot be kept in herbaria are preserved in museums.
For example, algae, fungi, mosses, ferns, fruits, etc. Specimens are preserves in containers or jars in preservative solutions. Plant and animal specimens may also be preserved as dry specimens. Insects are preserved in insect boxes after collecting killing and pinning. While, the larger animals are stuffed and preserved in skeletal forms.
4. Zoological Parks Zoological parks or zoo are the places where wild animals are kept in protected environments under human care and which enable us to learn about their food habits and behaviour. Zoological parks provide natural habitat to the animals. In India there are about 200 zoological parks. These zoos are managed by the Central Zoo Authority of India. The World Zoo Conservation Strategy (WZCS) refer to all these zoological institutions as zoos. Role of Zoological Parks (a) The zoological parks increase understanding of wildlife. (b) These are the centres for recreation and education. (c) Zoos are the centres for conservation of threatened and rare animal species. (d) These provide sites for ex situ breeding of endangered animals. conservation through captive breeding of endangered animals.
5. Key Key is also a taxonomical aid used for identification of plants and animals based on the similarities and dissimilarities. It helps in the identification of plants and animals by selecting and eliminating the characters according to their presence or absence in the organism under study. The keys generally use two contrasting characters called couplet. This results in acceptance of one present in organism and rejection of the other. Each statement in the key is called a lead. These taxonomic keys are of two types
Indented Key The indented key or yolked key provides a sequence of choices between two or more characteristics. By careful selection of characters at each sub-division, the exact name of the organism can be arrived at.
Bracketed Key The bracketed key also uses contrasting characters like the indented key. But in, these characters are not separated by intervening sub-dividing characters. Each character in this case is given a number in brackets.
Other Means of Recording Descriptions Apart from the all mentioned means of keeping records of description. Some other means are also present.
These are of following types Flora Floras are the important resource that provide information on the taxonomy, nomenclature and descriptive data for the taxa covered. The floras also include information on the biology, distribution and habitat preferences of the taxa, as well as illustrations, identification keys and other notes. These provide index to the plant species found in a particular area.
Manuals and Catalogues These are other means of recording descriptions. They also help in correct identification. Manuals are useful in providing information for identification of names of species found in an area.
Monograph A monograph is a comprehensive treatment of a taxon in biological taxonomic studies. These contain information on any one taxon. Monographs revise all known species within a group, add any newly discovered species, collect and organise available information on the ecological associations, geographic distributions and morphological variations within the group. The first ever monograph of a plant taxon was given in Robert Morison (1672) Plantarum Umbelliferarum Distributio Nova.
Interrelation of biological, social, economical, physical and chemical studies with our surrounding is called environmental studies. Environmental pollution is the greatest health hazard all over the world. Environmental chemistry deals with the study of the origin, transport reactions, effects and fates of chemical species in the environment.
An undesirable change in physical, chemical or biological characteristics of air, water and land that is harmful to human life and other living organisms, living conditions, cultural assets, industrial progress and harms our resources is called pollution.
Environmental Pollution
Undesirable changes that have harmful effects on plants, animals and human beings in our surrounding is called environmental pollution.
Pollutant
The substance which causes pollution and is harmful for environment is called pollutant. Pollutants are of two types :
(i). Biodegradable
Those substances which are degraded rapidly by natural process or artificial methods are called biodegradable pollutants. Ex- discarded vegetables.
(ii). Non-biodegradable
Those substances which degrade at very slow rate or does not degrade by natural biological process, for example, DDT, arsenic salts of heavy metals, radioactive materials and plastics are non-biodegradable pollutants.
Atmospheric Pollution
Lowest layer of atmosphere is troposphere which have dust, water vapour and clouds, it contains dust, water vapour and clouds while stratosphere contains ozone. Atmospheric pollution includes both troposphere and stratosphere pollution.
(i). Tropospheric Pollution
Tropospheric pollution occurs due to the presence of undesirable solid or gaseous particles in the air.
Gaseous air pollutants
(a) Oxides of Sulphur: Oxides of sulphur are produced when sulphur containing fossil fuel is burnt. The most common species, sulphur dioxide, is a gas that is poisonous to both animals and plants. It has been reported that even a low concentration of sulphur dioxide causes respiratory diseases e.g., asthma, bronchitis, emphysema in human beings. Sulphur dioxide causes irritation to the eyes, resulting in tears and redness.
2SO2 + O2 ⟶ 2SO3
(b) Oxides of Nitrogen : Mainly produced by combustion of fossil fuels at high temperature in automobile engines mainly NO and NO2.
These produce reddish brown haze or brown air NO2 is more dangerous than NO. These oxides can cause pulmonary oedema, dilation of arteries, eye irritation, heart problems, injury to liver and kidneys and also causes acid rains.
N2 + O2 ⟶ 2NO
2NO + O2 ⟶ 2NO2
(c) Hydrocarbons : Produced naturally (e.g., marsh gas) as well as due to incomplete combustion. These are carcinogenic and causes irritation of mucous membrane, eyes. They causes ageing, breakdown of tissues, shedding of flower, leaves and twigs in plants.
(d) Carbon monoxide : It is colourless, odourless gas. It is produced by incomplete combustion of fuels, naturally it is produced by oceans or by decaying of organic matter by bacteria. It is poisonous because it combines with haemoglobin to form 300 more times stable carboxyhaemoglobin which reduces oxygen-carrying capacity of blood and results into giddiness, headache, decreased vision, cardiovascular malfunction and asphyxia. Cigarette smoke also contains a lot of CO which induces premature birth deformed babies and spontaneous abortions in pregnant women.
(e) Carbon dioxide : It is produced naturally by volcanic eruptions, respiration. It is also produced by burning of fossil fuels. Increased level of CO2 is controlled by green plants during photosynthesis. It is a greenhouse gas and responsible for global warming. It causes headache nausea and asphyxiation.
Greenhouse Effect
This effect was discovered by Fourier and the term was coined by Arrhenius. 75% of solar radiation is absorbed by earth surface and remaining is reflected back. Some of which is absorbed by greenhouse gases such as carbon dioxide, methane, ozone, chlorofluorocarbon compounds (CFCs) and water vapour in the atmosphere which increases temperature of atmosphere is called greenhouse effect.
Acid Rain
When the pH value of the rain water drops below 5.6, it is known as acid rain. Acid rain is a byproduct of a variety of human activities that emit the oxides of sulphur and nitrogen in the atmosphere.
2SO2(g) + O2(g) + 2H2O(l) ⟶ 2H2SO4(aq)
(ii). Stratospheric Pollution
Ozone Hole
Depletion in the concentration of ozone over a restricted area as over Antarctica is called ozone hole. Stratospheric clouds are formed over Antarctica.
Molecular oxygen splits into free oxygen atoms by UV radiations which combine with molecular oxygen to form ozone.
O2(g) ⟶ [O](g) + [O](g)
[O](g) + O2(g) ⟶ O3(g)
As ozone is thermodynamically unstable hence, there exists dynamic equilibrium between its decomposition and formation. Ultraviolet radiations dissociate chlorofluorocarbon to give chlorine-free radical, which combines with ozone to form chlorine monoxide radical which combines with free oxygen to form more chlorine-free radicals.
CF2Cl2 ⟶ [C]F2Cl + [Cl]
[Cl] + O3 ⟶ Cl[O] + O2
2Cl[O] + O3 ⟶ 2[Cl] + 2O2
Effects of Depletion of The Ozone Layer
Bad ozone is formed in troposphere that harms plants and animals while good ozone is formed in stratosphere which acts as shield. UV rays can enter in earth’s atmosphere.
It is harmful as can cause skin cancer.
It increases transpiration hence decreases soil moisture.
It damages paints and fibres, causing them to fade faster.
Water Pollution
Any unwanted change which detiorate quality of water and make it unfit for drinking is called water pollution. Pollution of water originates from human activities.
Causes of Water Pollution
Organic matter such as leaves, grass, trash etc. as well as excessive phytoplankton growth in water causes water pollution as this matter is decomposed through microbial activity is known as putrescibility which requires oxygen. Degree of impurity of water due to organic matter is measured in terms of Biochemical Oxygen Demand (BOD).
Pathogens : Disease-causing agents are called pathogens e.g., viruses, bacteria, protozoa, helminthes, algae etc. Human excreta contains E.coli and Streptococcus faecalis bacteria which cause gastrointestinal diseases.
Chemical pollutants : These are of two types, inorganic and organic.Inorganic pollutants constitute acids, salts, heavy metals such as Cd, Hg, Ni etc. Heavy metals can damage central nervous system, liver and kidneys.Organic pollutants constitute, pesticides, petroleum pollutants, PCBs, detergents, fertilizers etc. PCBs (Polychlorinated Biphenyls) are carcinogenic and phosphatic fertilizers increase algae growth. Acidic water is harmful for aquatic life as well as for drinking.
Soil Pollution
It is unfavourable alteration of soil by addition or removal of substances and factors which decrease soil productivity, quality of plants and ground water is called soil pollution. Mainly caused by chemicals added into soil as pesticides, herbicides and fertilizers for better productivity.
Causes of Soil Pollution
Pesticides : These are actually synthetic toxic chemicals with ecological repercussions. These are used in killing pathogens, pests and in inhibiting unwanted growth in agriculture, horticulture, forestry and water.
Fertilizers : Excessive use of fertilizers decreases natural microflora hence detiorate soil. Therefore, now a days organic farming is encouraged which involves organic pesticides, biofertilizers and disease resistant varieties.
Industrial wastes : These are both solid and liquid and are dumped over the soil. These contain toxic chemicals like mercury, copper, zinc, lead, cadmium, cyanides, acid, alkalies etc
Strategies to Control Environmental Pollution
Two sources of environment pollutant are household waste and industrial waste. Following method can be used to control them.
Recycling : Waste are recycled into manufacturing of new material. For example, scrap iron, broken glass, clothes can be made from recycled plastic waste and soon becomes available in market. We can also recover energy from burning combustible waste.
Digestion : Waste material can be degraded by anaerobic micro-organisms in absence of air. It can be used to produce electricity. First biodegradable and non-biodegradable waste are separated then biodegradable wastes are mixed with water and cultured by bacterial species which produce methane.
Dumping : Sewage sludge acts as fertilizer because it contains nitrogen and phosphorus hence, it is dumped in land areas which increases soil fertility.
Green Chemistry
Green chemistry is a way of thinking and is about utilizing the existing knowledge and principles of chemistry and other sciences to reduce the adverse impact on environment. Utilization of existing knowledge base for reducing the chemical hazards along with the development activities are the foundation of green chemistry.
The term ‘hydrocarbon’ is self-explanatory meaning compounds of carbon and hydrogen only. Hydrocarbons hold economic potential in our daily life. Natural gas and petroleum are chief sources of aliphatic hydrocarbons at the present time, and coal is one of the major sources of aromatic hydrocarbons. Petroleum is a dark, viscous mixture of many organic compounds, most of them being hydrocarbons, mainly alkanes, cycloalkanes and aromatic hydrocarbons.
Classification
As we are quite aware that there are different types of hydrocarbons. Depending upon the types of carbon-carbon bonds present, they can be classified into three main categories –
saturated hydrocarbons
unsaturated hydrocarbons and
aromatic hydrocarbons.
Saturated hydrocarbons contain carbon-carbon and carbon-hydrogen single bonds. If different carbon atoms are joined together to form open chain of carbon atoms with single bonds, they are termed as alkanes. On the other hand, if carbon atoms form a closed chain or ring, they are termed as cycloalkanes. Unsaturated hydrocarbons contain carbon-carbon multiple bonds – double bonds, triple bonds or both. Aromatic hydrocarbons are a special type of cyclic compounds.
Alkanes
These are the saturated chains of hydrocarbons containing carbon-carbon single bonds. Methane (CH4), is the first member of this family containing single carbon atom. Since it is found in coal mines and marshy areas, is also known as ‘marsh gas’. These hydrocarbons exhibited low reactivity or no reactivity under normal conditions with acids, bases and other reagents, they were earlier known as paraffins. The general formula for alkane is CnH2n + 2, where n stands for number of hydrogen atoms in the molecule.
Structure of Methane
(A). Nomenclature
For nomenclature of alkanes in IUPAC system, the longest chain of carbon atoms containing the single bond is selected. Numbering of the chain is done from the one end so that maximum carbon will be included in chain. The suffix ‘ane’ is used for alkanes. The first member of the alkane series is CH4 known as methylene (common name) or methene (IUPAC name). IUPAC names of a few members of alkenes are given below :
S.No.
Structure
IUPAC Name
1.
CH4
Methane
2.
C2H6
Ethane
3.
C3H8
Propane
4.
C4H10
Butane
5.
C5H12
Pentane
6.
C6H14
Hexane
7.
C7H16
Heptane
8.
C8H18
Octane
9.
C9H20
Nonane
10.
C10H22
Decane
(B). Preparation of Alkanes
Though petroleum and natural gas are the main sources of alkanes, it can be prepared by several other methods as well.
1. From unsaturated hydrocarbons
The addition of dihydrogen to unsaturated hydrocarbons like alkenes and alkynes in the presence of a suitable catalyst under a given set of conditions produces saturated hydrocarbons or alkanes. This process of addition of dihydrogen is known as hydrogenation process.
CH2＝CH2 + H2 ⟶ CH3-CH3
CH☰CH + 2H2 ⟶ CH3-CH3
2. From alkyl halides
(a) Reduction: Alkyl halides undergo reduction with zinc and dilute hydrochloric acid to give alkanes. In general the reaction can be represented as
CH3-Cl ⟶ CH4
(b) Wurtz reaction: Alkyl halides on treatment with sodium metal in dry ether give higher alkanes. This reaction is known as Wurtz reaction.
CH3Br + 2Na + BrCH3 ⟶ CH3-CH3 + 2NaBr
3. From carboxylic acids
(a) By decarboxylation of carboxylic acids: Sodium salts of carboxylic acids on heating with soda lime give alkanes containing one carbon atom less than the carboxylic acid. A molecule of carbon dioxide is eliminated which dissolves in NaOH to form sodium carbonate.
CH3COONa + NaOH ⟶ CH4 + Na2CO3
(b) Kolbe’s electrolytic method: An aqueous solution of sodium or potassium salt of a carboxylic acid on electrolysis gives alkane containing even number of carbon atoms at anode.
CH3COONa + 2H2O ⟶ CH3-CH3 + 2CO2 + H2 + NaOH
(C). Properties of Alkanes
I. Physical Properties
(i) State: Due to the weak van der Waals forces, the first four members C1 to C4 i.e., methane, ethane, propane and butane are gases. From C5 to C17 are liquids and those containing 18 carbon atoms or more are solids at 298 K. They all are colourless and odourless.
(ii) Solubility: Alkanes are generally insoluble in water or in polar solvents but they are soluble in non-polar solvents like, ether, benzene, carbontetrachloride etc. The solubility of alkanes follow the property “Like Dissolves like”.
(iii) Boiling point: The boiling points of straight chain alkanes increase regularly with the increase of number of carbon atoms. This is due to the fact that the intermolecular van der Waals forces increase with increase in the molecular size or the surface area of the molecule.
II. Chemical Properties
Generally alkanes show inertness or low reactivity towards acids, bases, oxidizing and reducing agents at ordinary conditions because of their non-polar nature and absence of π bond. The C–C and C–H bonds are strong sigma bonds which do not break under ordinary conditions but they undergo certain reactions under given suitable conditions.
(1) Halogenation reaction: When hydrogen atom of an alkane is replaced by a halogen, it is known as halogenation reaction. Halogenation takes place either at high temperature (300–500°C) or in the presence of diffused sunlight or ultraviolet light.
CH4 + Cl2 ⟶ CH3Cl + HCl
(2) Combustion: Alkanes on heating in presence of air gets completely oxidized to carbon dioxide and water. It burns with a non-luminous flame. The combustion of alkanes is an exothermic process i.e., it produces a large amount of heat.
CH4 + 2O2 ⟶ CO2 + 2H2O
(3) Controlled oxidation: When methane and dioxygen compressed at 100 atm are passed through heated copper tube at 523 K yield methanol.
2CH4 + O2 ⟶ 2CH3OH
(4) Aromatization: The conversion of aliphatic compounds into aromatic compounds is known as aromatisation. n-Alkanes having six or more carbon atoms on heating to 773 K at 10–20 atmospheric pressure in the presence of oxides of vanadium, molybdenum or chromium supported over alumina get dehydrogenated and cyclised to benzene and its homologues. This reaction is also known as reforming.
(5) Reaction with steam: Methane reacts with steam at 1273 K in the presence of nickel catalyst to form carbon monoxide and dihydrogen. This method is used for industrial preparation of dihydrogen gas.
CH4 + H2O ⟶ CO + 3H2
Alkenes
Alkenes are unsaturated hydrocarbons containing at least one carbon-carbon double bond with general formula CnH2n. Alkenes are also known as olefins (oil forming) since the first member, ethylene or ethene (C2H4) was found to form an oily liquid on reaction with chlorine.
(A). Nomenclature
For nomenclature of alkenes in IUPAC system, the longest chain of carbon atoms containing the double bond is selected. Numbering of the chain is done from the end which is nearer to the double bond. The suffix ‘ene’ replaces ‘ane’ of alkanes. The first member of the alkene series is C2H4 known as ethylene (common name) or ethene (IUPAC name). IUPAC names of a few members of alkenes are given below :
S.No.
Structure
IUPAC Name
1.
C2H4
Ethene
2.
C3H6
Propene
3.
C4H8
Butene
4.
C5H10
Pentene
5.
C6H12
Hexene
6.
C7H14
Heptene
7.
C8H16
Octene
8.
C9H18
Nonene
9.
C10H20
Dekene
(B). Preparation
1. From alkynes: Alkynes undergo partial reduction with calculated amount of dihydrogen producing alkenes.
CH☰CH + H2 ⟶ CH2＝CH2
2. From alkyl halides: Alkyl halides (R–X) on heating with alcoholic potash eliminates one molecule of halogen acid to form alkenes. This reaction is known as dehydrohalogenation i.e., removal of halogen acid.
CH3CH2Cl ⟶ CH2＝CH2 + HCl
3. From alcohols by acidic dehydration: Alcohols on heating with concentrated sulphuric acid form alkenes with the elimination of one water molecule since a water molecule is eliminated from the alcohol molecule in the presence of an acid, this reaction is known as acidic dehydration of alcohols.
CH3CH2OH ⟶ CH2＝CH2 + H2O
(C). Properties of Alkenes
I. Physical properties
The first three members of alkenes are gases, the next fourteen are liquids and the higher ones are solids.
Ethene is a colourless gas with a faint sweet smell. All other alkenes are colourless and odourless, insoluble in water but fairly soluble in non-polar solvents like benzene, petroleum ether.
They show a regular increase in boiling point with increase in size i.e., every —CH2 group added increase the boiling point by 20–30 K.
II. Chemical properties
1. Addition of dihydrogen: Alkenes adds one mole of dihydrogen gas in presence of catalysts such as Ni at 200–250°C, or finely divided Pt or Pd at room temperature to give an alkane.
CH2＝CH2 + H-H ⟶ CH3-CH3
2. Addition of halogens: Halogens like bromine or chlorine add up to alkene to form vicinal dihalides in presence of CCl4 as solvent. The order of reactivity of halogens is F > Cl > Br > I.
CH2＝CH2 + Br-Br ⟶ Br-CH2-CH2-Br
3. Addition of hydrogen halides: Hydrogen halides (HCl, HBr, HI) add upto alkenes to form alkyl halides. The order of reactivity of hydrogen halides is HI > HBr > HCl. Like addition of halogens to alkenes, addition of hydrogen halides is an example of electrophilic addition reaction.
CH2＝CH2 + H-Br ⟶ CH3-CH2-Br
Markovnikov rule: According to the rule, the negative part of the addendum (adding molecule) adds to that carbon atom of the unsymmetrical alkene which is maximum substituted or which possesses lesser number of hydrogen atoms.
CH3CH＝CH2 + HBr ⟶ CH3-CH(Br)-CH3
Anti Markovnikov addition or Peroxide effect or Kharash effect: In the presence of peroxide, addition of HBr to unsymmetrical alkenes like propene takes place contrary to the Markovnikov rule. This happens only with HBr but not with HCl or HI. This reaction is known as peroxide or Kharash effect or addition reaction anti to Markovnikov rule.
CH3CH＝CH2 + HBr ⟶ CH3-CH2-CH2-Br
4. Polymerisation: Polymerisation is the process where monomers combines together to form polymers. The large molecules thus obtained are called polymers. Other alkenes also undergo polymerisation.
n(CH2＝CH2) ⟶ (-CH2-CH2-)n
Alkynes
Like alkenes, alkynes are also unsaturated hydrocarbons with general formula CnH2n – 2. They contain at least one triple bond between two carbon atoms. These have four H-atoms less compared to alkanes. The first stable member of alkyne series is ethyne commonly known as acetylenes.
(A). Nomenclature
In common system, alkynes are named as derivatives of acetylene. In IUPAC system, they are named as derivatives of the corresponding alkanes replacing ‘ane’ by the suffix ‘yne’. The position of the triple bond is indicated by the first triply bonded carbon. Common and IUPAC names of a few members of alkyne series are given in the table below :
S.No.
Structure
IUPAC Name
1.
C2H2
Ethyne
2.
C3H4
Propyne
3.
C4H6
Butyne
4.
C5H8
Pentyne
5.
C6H10
Hexyne
(B). Preparation
1. From calcium carbide: On industrial scale, ethyne is prepared by reacting calcium carbide with water. Calcium carbide is prepared by heating quick lime with coke. Quick lime can be obtained by heating limestone as shown in the following reactions :
CaCO3 ⟶ CaO + CO2
CaO + 3C ⟶ CaC2 + CO
CaC2 + 2H2O ⟶ Ca(OH)2 + C2H2
2. From vicinal dihalides: Vicinal dihalides on treatment with alcoholic potassium hydroxide undergo dehydrohalogenation. One molecule of hydrogen halide is eliminated to form alkenyl halide which on treatment with sodamide gives alkyne.
CH2(Br)-CH2(Br) + KOH ⟶ CH2＝CH2 ⟶ CH☰CH
(A). Properties of Alkynes
I. Physical properties
The first three members (acetylene, propyne and butynes) are gases, the next eight are liquids and higher ones are solids.
All alkynes are colourless. All alkynes except ethyne which have an offensive characteristic odour, are odourless.
Alkynes are weakly polar in nature and nearly insoluble in water. They are quite soluble in organic solvents like ethers, carbon tetrachloride and benzene.
Their melting point, boiling point and density increase with increase in molar mass.
II. Chemical properties
(i) Addition of dihydrogen: Alkynes contain a triple bond, so they add up, two molecules of dihydrogen.
CH☰CH + H2 ⟶ CH2＝CH2 ⟶ CH3-CH3
(ii) Addition of halogens: Alkynes contain a triple bond, so they add up, two molecules of halogen.
CH☰CH + Cl2 ⟶ CH(Cl)＝CH(Cl) ⟶ CH(Cl)2-CH(Cl)2
(iii) Addition of hydrogen halides: Two molecules of hydrogen halides (HCl, HBr, HI) add to alkynes to form gemdihalides (in which two halogens are attached to the same carbon atom).
CH☰CH + HCl ⟶ CH2＝CH(Cl)
(iv) Addition of water: Like alkanes and alkenes, alkynes are also immiscible and do not react with water. However, one molecule of water adds to alkynes on warming with mercuric sulphate and dilute sulphuric acid at 333 K to form carbonyl compounds.
CH☰CH + H2O ⟶ CH3-CHO
(v) Polymerisation: Ethyne on passing through red hot iron tube at 873 K undergoes cyclic polymerization. Three molecules polymerise to form benzene, which is the starting molecule for the preparation of derivatives of benzene, dyes, drugs and large number of organic compounds.
(vi) Oxidation:
2C2H2 + 5O2 ⟶ 4CO2 + 2H2O
Aromatic Hydrocarbon
Aromatic hydrocarbons are also known as ‘arenes’. Since most of them possess pleasant odour (Greek; aroma meaning pleasant smelling), the class of compounds are known as ‘aromatic compounds’. Most of the compounds are found to have benzene ring. Benzene ring is highly unsaturated and in a majority of reactions of aromatic compounds, the unsaturation of benzene ring is retained. Aromatic compounds containing benzene ring are known as benzenoids and those, not containing a benzene ring are known as non-benzenoids.
Nomenclature
Since all the six hydrogen atoms in benzene are equivalent; so it forms one and only one type of monosubstituted product. When two hydrogen atoms in benzene are replaced by two similar or different monovalent atoms or groups, three different position isomers are possible which differ in the position of substituents. So we can say that disubstituted products of benzene show position isomerism. The three isomers obtained are 1, 2 or 1, 6 which is known as the ortho (o-), the 1, 3 or 1, 5 as meta (m-) and 1, 4 as para (p-) disubstitued compounds.
(B). Structure
The molecular formula of benzene, C6H6, indicates a high degree of unsaturation. All the six carbon and six hydrogen atoms of benzene are identical. On the basis of this observation August Kekule in 1865 proposed the following structure for benzene having cyclic arrangement of six carbon atoms:
(C). Resonance
Even though the double bonds keep on changing their positions. The structures produced is such that the position of nucleus remains the same in each of the structure. The structural formula of such a compound is somewhat intermediate (hybrid) between the various propose formulae. This state is known as Resonance.
(D). Preparation of Benzene
(i) Cyclic polymerisation of ethyne: Ethyne on passing through red hot iron tube at 873 K undergoes cyclic polymerization.
(ii) Decarboxylation of aromatic acids: Sodium salt of benzoic acid i.e., sodium benzoate on heating with sodalime gives benzene.
(iii) Reduction of phenol: Phenol is reduced to benzene by passing its vapour over heated zinc dust.
(E). Properties of Benzene
I. Physical Properties
Aromatic hydrocarbons are non-polar molecules and are usually colourless liquids or solids with a characteristic aroma.
The napthalene balls used in toilets and for preservation of clothes because of unique smell of the compound.
Aromatic compounds are insoluble in water but soluble in organic solvents such as alcohol and ether.
They burn with sooty flame.
II. Chemical Properties
(i) Nitration: A nitro group is introduced into the benzene ring when benzene is heated with a mixture of concentrated nitric acid and concentrated sulphuric acid.
(ii) Halogenation: Arenes undergo halogenation when it is treated with halogens in presence of Lewis catalyst such as anhy. FeCl3, FeBr3 or AlCl3 to yield haloarenes.
(iii) Sulphonation: The replacement of a hydrogen atom by a sulphonic acid group in a ring is called sulphonation. It is carried out by heating benzene with fuming sulphuric acid or oleum (conc. H2SO4 + SO3).
(iv) Friedel-Crafts alkylation reaction: When benzene is treated with an alkyl halide in the presence of anhydrous aluminium chloride, alkylbenzene is formed.
Activating Groups: Electron donating groups (EDG, +M, +I, +H. C. effect) in the benzene ring will more stabilize the σ-complex (Arenium ion complex) with respect to that of benzene and hence they are known as activator.
Deactivating Groups: Electron drawing groups (–M, –I effects) will destabilize σ-complex as compared to that of benzene. Therefore substituted benzenes where substituents are electron withdrawing decreases reactivity towards SE reactions.
Organic Chemistry Some Basic Principles and Techniques Class 11 Notes Chemistry
Structural Representations of Organic Compounds
(i). Structural Formulas
The lewis structures can be simplified by representing the two electron covalent bonds by a dash (–). In this representation, a single bond is represented by a single dash (–), a double bond by a double dash (=) and a triple bond by a triple dash (≡). The lone pair on an atom may or may not be shown. This representation is called structural formula.
(ii). Condensed Formulas
In this formula, the arrangement of atoms are shown but the bonds between may be omitted and the number of identical groups attached to an atom are indicated by a subscript.
(iii). Bond Line Formulas
In this representation, the carbon and hydrogen atoms are not shown and the lines between carbon-carbon bonds are shown in a zig-zag manner.
In cyclic compounds, the bond-line formulas may be given as follows :
Three-dimensional representation of organic molecules
The three-dimensional (3-D) structure of organic molecules can be represented on paper by using certain conventions. In these formulae, the thick solid (or heavy) line or the solid wedge indicates a bond lying above the plane of the paper and projecting towards the observer while a dashed wedge is used to represent a bond lying below the plane of the paper and projecting away from the observer.
Classification of Organic Compounds
On the basis of their structures, organic compounds are broadly classified as follows :
Open Chain Compounds
These compounds contain open chains of carbon atoms in their molecules. The carbon chains may be either straight chains or branched chains. They are also called aliphatic compounds.
Closed Chain or Ring Compounds
These compounds contain chains or rings of atoms in their molecules.
Alicyclic Compounds : These compounds contain a ring of three or more carbon atoms in them. They resemble aliphatic compounds in many of their properties.
Aromatic Compounds : These have a cyclic system containing at last one benzene ring. The parent member of the family is called benzene. Benzene has a homocyclic hexagonal ring of six carbon atoms with three double bonds in the alternate positions.
Heterocyclic Compounds : In these compounds, the ring contains one or more atoms of either nitrogen, oxygen or sulphur in addition to carbon atoms. The atom other than carbon (such as N, O, S) present in the ring is called hetero atoms.
Functional Groups : An atom or group of atoms which largely determines the properties of the organic compounds particularly the chemical properties.
Homologous Series : Homologous series may be defined as “a series of similarly constituted compounds in which the members possess the same functional group and have similar chemical characteristics”. The two consecutive members differ in their molecular formula by –CH2– group.
The term ‘nomenclature’ means the system of naming of organic compounds. There are two systems of nomenclature:
(i) Trivial or Common System
In this nomenclature, the names of organic compounds were assigned based on their source of origin or certain properties. For instance, citric acid got its name from the source (citrus fruits) from which it was first isolated. Formic acid was named so as it was first obtained from red ant. In Latin, ant word is formica.
(ii) IUPAC System of Nomenclature
A systematic method of naming has been developed and is known as the IUPAC (International Union of Pure and Applied Chemistry) system of nomenclature. In this systematic nomenclature, the names are correlated with the structure such that the reader or listener can deduce the structure from the name.
A. Nomenclature of Alkanes
(i). Straight Chain Hydrocarbons: The names of straight chain hydrocarbons consist of word root and primary suffix. The primary suffix for alkanes is ‘ane’.
The IUPAC names of some unbranched saturated hydrocarbons (Carbon-Carbon single bond) are given below.
(ii) Branched Chain Hydrocarbons: In branched chain hydrocarbons, small side chains of carbon atoms are attached to the main carbon parent chain. These side chains are called as alkyl groups and are prefixed t the name of parent alkane. Alkyl groups are derived from alkane by removal of one hydrogen atom so have general formula CnH2n+1 and represented by –R. An alkyl group is named by replacing ‘ane’ of the alkane to ‘yl’.
B. Branched Chain Hydrocarbons:
By following certain rules the branched chain hydrocarbons can be named without any difficulty:
(i) Longest Chain Rule: The initial step of nomenclature is to identify the longest carbon chain which is then called as parent chain.
(ii) Lowest Number Rule: The numbering of the parent chain is done in such a way that the substituents attached to the parent chain should get the lowest possible position.
(iii) Alphabetical Order of the Side Chain: The names of the alkyl group are prefixed before the nam of the parent chain. The position of the alkyl group is indicated by carefully numbering the parent chain Moreover care is taken to name of the substituents in the alphabetical order when different alkyl group are present as substituents.
(iv) In the IUPAC name of an organic compound, the numbers are separated by comma from each other, das or hyphen (-) is put between a number and a letter and the successive words are merged into one word If the branched hydrocarbon contains more than one alkyl groups, then their names are not repeated, instead the number of the same alkyl substituents is written by prefix di for two, tri for three, tetra fo four, penta for five, hexa for six etc.
(v) When the organic compound has more than one alkyl group, then their names are written in the alphabetical order but the prefixed di, tri etc. are not considered for alphabetical order. Thus the correc name of the following compound is 3-ethyl-4, 4-dimethylheptane.
(vi) Numbering of Different Alkyl Groups at Equivalent Positions: When the two different alkyl groups are present at the equivalent positions, then the numbering of the parent chain is done in such a wa so as to assign the lower number of the alkyl group which comes first in the alphabetical order.
(vii) Cyclic Compounds: For naming cyclic hydrocarbons ‘cyclo’ prefix is used before the name of parent chain and the remaining rules are same as explained earlier.
Nomenclature of Unsaturated Hydrocarbons
(i) Select the longest possible carbon chain having maximum number of unsaturated carbon atoms or maximum number of double or triple bonds, even if the prior rules are violated.
(ii) Hydrocarbon containing both C=C and C☰C: When hydrocarbon contains one double bond and one triple bond they are called alkenynes (not alkynenes). The parent chain is numbered in such a way that multiple bond (double or triple) is assigned the lowest possible number. When these bonds are located at equivalent positions, the double bond is given priority over the triple bond.
Nomenclature of Organic Compounds having functional group
Functional Group: Functional group may be defined as an atom or a group of atoms bonded together in a unique manner present in a molecule which largely determines its chemical properties.
The presence of a functional group is indicated by either adding their suffixes or prefixes. The prefixes and suffixes of same functional groups are given in the following table.
The organic compounds with same functional group show similar chemical properties. For example, alcohols like CH3OH, CH3CH2OH,(CH3)2CHOH, etc, all produce hydrogen when treated with sodium metal.
Identify functional groups.
Decide the principal functional group according to its position in priority list. The principal functional group is identified by suffix and the other functional group by prefixes.
Select the longest chain containing the functional groups including C＝C or C☰C bond or both as the main chain and name the hydrocarbon on the basis of number of carbons in the main chain.
Derive from the hydrocarbon name the parent name of the compound for the principal functional group.
Assign number of carbon atoms in the main chain so that the principal functional group is given the lowest possible number.
Put the positional number for the functional group, if necessary in the parent name at suitable place.
Complete the name of the compound by placing substituents just before the parent name.
Nomenclature of Substituted Benzene Compounds
(1) For naming the substituted benzene compounds, the prefix used for the substituent is prefixed to the word ‘benzene’ simply.
(2) Many substituted benzene compounds are universally known by their common names.
Isomerism
Such organic compounds which have the same molecular formula but differ from each other in their properties are called as isomers and the phenomenon is called as isomerism. It is of two types:
Structural isomerism
Stereoisomerism
1. Structural Isomerism: Compounds having the same molecular formula but different structure are called structural isomers and the phenomenon is called structural isomerism. It is also known as constitutional isomerism. It is of the following types:
(i) Chain Isomerism: The compounds having same molecular formula but different chain of carbon atom. For example: Butane and 2-methyl propane are chain isomers.
(ii) Position Isomerism: Compounds having the same molecular formula but different in position substituents, C = C, C ≡ C or functional group are called position isomers.
(iii) Functional Isomerism: The compounds having same molecular formula but different functional groups in the molecule are called functional isomers.
(iv) Metamerism: The compounds having same molecular formula but different alkyl group on either side of the functional group, are called metamers.
(v) Tautomerism: When two or more constitutionally distinct compounds are in dynamic equilibrium because of the shift of an atom (generally proton) from one place to another place in a molecule. The phenomenon is called Tautomerism and various constitutional isomers are known as tautomers.
2. Stereoisomerism: Isomers which have the same structural formula but have different relative arrangement of atoms or groups in space are called stereoisomers and the phenomenon is called stereoisomerism. It has three types:
Geometrical Isomerism
Conformational Isomerism
Optical Isomerism
(i) Geometrical Isomerism: When two compounds differ in spatial arrangement of groups because of restricted rotation, these compounds are known as geometrical isomers.
Fundamental Concepts in Organic Reaction Mechanism
A. Fission of a Covalent Bond
Organic reactions usually involve making and breaking of covalent bonds. The fission of bonds can take place in two ways:
(i) Heterolytic Fission: When a covalent bond between two atoms A & B breaks in such a way that both the electrons of the covalent bond are taken away by one of the bonded atoms, the mode of bond cleavage is called heterolytic fission. Heterolytic fission is usually indicated by a curved arrow (↷) which denotes a two-electron displacement.
(ii) Homolytic Fission: If a covalent bond breaks in such a way that each atom takes away one electron of the shared pair, it is called homolytic or symmetrical fission. Homolytic fission is usually indicated by a fish arrow (↶↷) which denotes a one-electron displacement.
B. Attacking Reagents
(i) Electrophiles: A reagent that takes away an electron pair is called electrophile. There are positively charged or neutral species which are deficient of electrons and can accept a pair of electrons. They are also called electron-loving (philic) or electron-seeking species (E). Ex- H+, H3O+, Cl+, CH3+, NO2+, AlCl3, BF3 etc.
(ii) Nucleophiles: A reagent that brings an electron pair is called nucleophile. These reagent contain an atom having unshared or lone pair of electrons. A nucleophile is electron-rich and seeks electron-deficient sites i.e., nucleus-loving or nucleus-seeking (Nu). According to lewis concept of acids and basis, nucleophiles behave as lewis bases. Ex- X– OH–, CN–, RCOO–, NH3, H2O etc.
Electron Displacements in Covalent Bonds
(a) Inductive Effect (I-effect): This is a permanent effect which arises whenever an electron-withdrawing group is attached to the end of a carbon chain. To understand this, let us consider a chain of carbon atoms having Cl atom at one end.
C4-C3-C2-C1-Cl
Hence, Cl-atom is more electronegative than C so, the σ-electrons of the C—Cl -bond are attracted by or displaced towards the more electronegative atom. As a result, the atom Cl acquires a small negative charge (δ–) and C1 acquires a small positive charge (δ+) as shown below.
C4-C3-C2-C1δ+-Clδ-
(i) –I effect: If the substitutent attached to the end of the carbon chain is electron-withdrawing, the effect is called –I effect.
(ii) + I effect: If the substituent attached to the end of the carbon chain is electron-donating, the effect is called +I effect.
Applications
Acidic and Basic strength of various organic acids and bases can be explained through this effect.
Stability of carbocations and carbanions.
Reactivity of alkyl halides.
Diplole moment, bp, mp etc.
(b) Electromeric Effect (E-effect): It is temporary effect which operates in the organic compounds having multiple bonds i.e., double or triple bonds under the influence of an outside attacking species. As a result, one pi electron pair of the multiple bond gets completely transferred to one of the bonded atoms which is usually more electronegative.
The electromeric effect is shown by a curved arrow (↷) representing the electron transfer originating from the centre of the multiple bond and pointing towards one of the atoms which is more electronegative.
(i) +E effect: If the pi-electron pair of the multiple bond is transferred to the atom to which the attacking reagent gets attached, then the effect is called +E effect.
(ii) –E effect: In this case the pi-electron pair of the multiple bond is transferred away from the atom which gets linked to the attacking reagent, the effect is known as –E effect.
(c) Resonance or Mesomeric Effect (R-effect): The phenomenon of exhibiting more than one possible structure is called as resonance. The resonance can be explained clearly on the basis of structure of benzene. The benzene can be represented by following two canonical form.
(i) + R effect: If a conjugated system has an electron-donating group is said to have + R or + M effect. Such as –OH, –OR, –SH, –NH2, –NHR, –X (halogen) etc.
(ii) –R or –M Effect: If a conjugated system has an electron-withdrawing group is said to have – R or – M effect. Such as –CHO, –COOH, –COOR, –CN, –NO2, >C=O etc.
Aromaticity
Huckel’s Rule of Aromaticity
Huckel’s rule is valid for compounds containing atleast:
(4n+2)π electrons where n is either zero or positive integer.
Hypercojugation
When an alkyl group is attached to an unsaturated system such as double bond or a benzene ring. The order of inductive effect is actually reversed. This effect is called hyperconjugation effect or Baker-Nathan effect.
Reaction Intermediates
The species produced during cleavage of bonds are called reaction intermediates, these are generally short-lived and highly reactive and hence cannot be isolated. The typical intermediates are:
(i) Carbocations: A carbocation may be defined as “A group of atoms with a positively charged carbon atom having six electrons in the valence shell after sharing”.
(ii) Carbanions: It may be defined as “chemical species bearing a negative charge on carbon and possessing eight electrons in its valence shell are called carbanions”.
(iii) Free Radicals: It may be defined as “an atom or group of atoms with an odd or unpaired electron.”
Types of Reactions
There are basically four types of reaction:
Addition reaction
Elimination reaction
Substitution reaction
Rearrangement
(i) Addition Reaction: In which a group adds to the system, unsaturated organic compounds comes under this category e.g.
CH2 = CH2 + H2 → CH3—CH3
(ii) Elimination Reaction: The reactions in which two atoms or groups of the molecule are removed are called elimination reactions.
CH3—CH2Br → CH2 = CH2 + HBr
(iii) Substitution Reaction: When a group is removed and another group takes its place. These can also be called displacement reactions. The displacement of the halide group by an OH group to form alcohol.
CH3Cl + KOH → CH3OH + KCl
(iv) Rearrangement: When the molecule rearranges itself by shifting its own part to some other site within the molecule. This is done to attain higher stability if it can be achieved. The various isomerization reactions come under this category.
CH3—CH2—CH2+ → CH3—CH+—CH3
Methods of Purification of Organic Compounds
The organic compounds whether isolated from a natural source or prepared in the laboratory are mostly impure. These are generally contaminated with some other substances. A number of methods are available for the purification. The choice of a particular technique or method depends upon the nature of the compound whether solid or liquid and also upon the nature of the impurities associated with it. The common techniques used for purification are as follows:
Sublimation
Crystallisation
Distillation
Differential extraction
Chromatography
(i) Sublimation: Certain organic solids on heating directly change from solid to vapour state without passing through a liquid state. Such substances are called sublimable. This process is called sublimation. The vapours on cooling change back to the solid form. The sublimation process is used for the separation of sublimable volatile compounds such as camphor, naphthalene, anthracene, benzoic acid etc.
Solid ⇌ Vapour
(ii) Crystallisation: This is the most common method for purifying organic solids. This method is based on the differences in the solubility of the organic compound and its impurities in a suitable solvent.
(iii) Distillation: “Distillation is the process of converting a liquid into vapours upon heating and then cooling the vapours back to the liquid state”. The process of simple distillation is used to purify those organic liquids which are quite stable at their boiling points and the impurities present are non-volatile. Liquids such as benzene, toluene, ethanol, acetone, chloroform, carbon tetrachloride can be purified by simple distillation.
(iv) Differential Extraction: This technique is normally used to separate certain organic solids dissolved in water by shaking with a suitable organic solvent. The process called extraction is done in a separating funnel. The organic solvent selected should be such that (a) The given solid must be more soluble in the organic solvent than in water. (b) Water and organic solvent should not be miscible with each other.
(v) Chromatography: Chromatography is a modern and sensitive techniques used for rapid and efficient separation or analysis of components of a mixture and purification of the compounds. “The technique of separating the components of a mixture in which separation is achieved by the differential movement of individual components through a stationary phase under the influence of a mobile phase”.
Qualitative Analysis of Organic Compounds
In the study of any organic compound, it is an important step to know the elements present in it. In addition to carbon and hydrogen, organic compounds contain some other elements, e.g., nitrogen, sulphur, halogens, etc. These are detected as follows:
(a) Detection of Carbon and Hydrogen: Carbon and hydrogen are detected by heating the compound with copper (II) oxide. Carbon present in the compound is oxidised to carbon dioxide and hydrogen to water vapours.
C + 2CuO ⟶ 2Cu + CO2
(b) Test for Nitrogen: About 2 ml of sodium extract is taken in a test tube and made alkaline by adding NaOH solution. To this reaction mixture is added freshly prepared FeSO4 solution and boiled for 3–4 minutes. The formation of Prussian blue colour or precipitate shows the presence of nitrogen.
Na + C + N ⟶ NaCN
(c) Test for Sulphur: If organic compound contains both nitrogen and sulphur, sodium thiocyanate is formed.
Na + C + N + S ⟶ NaSCN
(d) Test for Halogens: A portion of the sodium extract is Boiled with 2–3 ml concentrated HNO3 followed by cooling and addition of AgNO3 solution when a pale yellow precipitate partially soluble in ammonia solution indicates the presence of bromine.
The elements in which last electron enters into p-subshell are called as p-block elements. The number of p-orbitals is three and, therefore, the maximum number of electrons that can be accommodated in a set of p-orbitals is six, hence p-block contains six groups.
Boron Family
Group III A contains six elements : boron, aluminium, gallium, indium, thallium and ununtrium. The penultimate shell (next to the outermost) conains 1s2 in boron, 2s2 2p6 (8 electrons) in aluminium and (n–1)s2(n–1)p6(n–1)d10 (18 electrons) in other elements.
Boron is a non-metal and always form covalent bonds. Boron family is known as most heterogeneous family as there is no regular trend in all properties, as it comes after d-block, lanthanoid contraction, poor shielding of d-orbital, they have large deviation in properties.
I. Physical Properties
The atomic radius, ionic radius and density increases when one moves from top to bottom in a group in periodic table. While melting point decreases from B to Ga and then increases from (Ga to In). Ionisation energy decreases from B to Al, but shows a reverse trend in going from Al to Ga.
II. Chemical Properties
1. Reaction with air: Impure boron in air forms oxide while pure boron is less reactive.
4B + 3O2 ⟶ 2B2O3
2. Reaction with water: Boron is not affected by water or steam under ordinary conditions. However, Aluminium reacts with cold water if oxide layer is not present on its surface.
4Tl + 2H2O + O2 ⟶ 4TlOH
3. Reaction with acids: Boron is not affected by non-oxidising acids like HCl and dilute H2SO4 while other elements dissolve and liberate H2 gas.
2Al + 6HCl ⟶ 2AlCl3 + 3H2
4. Reaction with alkalies: Boron, Aluminium, Gallium react with alkali solutions whereas Indium and Thallium are not affected by alkalies.
2B + 6NaOH ⟶ 2Na2BO3 + 3H2
Anomalous Properties of Boron
Boron, the first member of group 13 elements, shows anomalous behaviour and differ from rest of the members of its family. The main reason for this difference are :
exceptionally small atomic and ionic size.
high ionization enthalpy.
absence of d orbital in its valence shell.
It has higher melting and boiling point than those of the other members of its group.
Compounds of Boron
[A]. Borax/Sodium Tetraborate (Na2B4O7·10H2O)
It is the most important compound of boron. It is a white crystalline solid. Borax dissolves in water to give an alkaline solution.
I. Preparation
From Boric acid: Boric acid is neutralised with sodium carbonate and the resulting solution is cooled to get crystals of borax.
H3BO3 + Na2CO3 ⟶ Na2B4O7 + H2O + CO2
II. Properties
(i) It gets hydrolysed with water to form an alkaline solution
Na2B4O7 + 7H2O ⟶ 2NaOH + H3BO3
(ii) Borax bead test: On heating borax first swells up due to elimination of water molecules. On further heating it melts to a liquid which then solidifies to a transparent glassy mass.
Na2B4O7.10H2O ⟶ Na2B4O7 + 10H2O
Na2B4O7 ⟶ 2NaBO2 + B2O3
(iii) It is a useful primary standard for titration against acids.
The simplest boron hydride known, is diborane. It is prepared by treating boron trifluoride with LiAlH4 in diethyl ether.
I. Preparation
3LiAlH4 + 4BCl3 ⟶ 3LiCl + 3AlCl3 + B2H6
II. Properties
(i) Stable at low temperature only, colourless and highly toxic.
(ii) B2H6 + 6H2O ⟶ 2H3BO3 + 6H2
(iii) B2H6 + 6Cl2 ⟶ 2BCl3 + 6HCl
(iv) B3H6 + 2Me3N ⟶ 2[Me3N.BH3]
Uses of Boron and Aluminium and Their Compounds
Boron Compounds
Boron is a hard solid having high melting point low density and very low electrical conductivity. Some important boron compounds are :
(a) Boron fibers: It is mixed with plastic to form a material which is lighter than aluminium but tougher and stiffer than steel hence it is used in body armour, missiles and aircrafts.
(b) Boron-10 (10B) isotope: Boron carbide rods or boron steel are used to control nuclear reactions as neutron absorbers.
5B10 + 0n1 ⟶ 5B11
(c) Borax: It is used in manufacture of enamels and glazes for pottery and tiles. It is also used in making optical glasses and also borosilicate glasses which is very resistant to heat and shock. It is used as an antispectic.
(d) Boric acid: It is used in glass industry, in food industry as preservative. It is also used as an antiseptic and eye wash under the name ‘boric lotion’. It is also used in manufacture of enamels and glazes for pottery.
(e) Boron carbide: Hardest boron compound.
I. Aluminium Compounds
Aluminium and its alloy are used in packing industry, utensil industry, aeroplane and transportation industry etc.
1. Alumina (Al2O3)
(a) Used in chromatography.
(b) Used in making bauxite bricks which are used for lining furnaces.
2. Aluminium chloride (AlCl3): Used in manufacture of dyes, drugs and perfumes and also in manufacture of gasoline. It is also used as catalyst in Friedel Craft reaction.
3. Potash Alum. [K2SO4⋅Al2(SO4)3⋅24 H2O]: Used in purification of water, leather tanning, as antiseptic and as a mordant.
Group 14 Elements : The Carbon Family
Group IV A contains six elements : carbon, silicon, germanium, tin, lead and ununquadium. The penultimate shell (prior to outermost) contains 1s2 -grouping in carbon, 2s22p6 (8 electrons) in silicon and (n–1)s2(n–1)p6(n–1)d10 (18 electrons) in other elements. This shows why carbon differs from silicon in some respects and these two differ from rest of the members of this group. General electronic configuration is ns2np2.
[A]. Atomic and Physical Properties
The important properties of carbon family are discussed below:
(1) Atomic Radii: The atomic radii of group 14 elements are less than the corresponding elements of group 13. However, the atomic radii increases down the family.
(2) Ionisation Energies: The higher ionisation energies than group 13 are due to the higher nuclear charge and smaller size of atoms of group 14 elements. While moving down the group, the ionisation energies decreases till Sn.
C > Si > Ge > Sn < Pb
(3) Oxidation state and valency: The elements of group 14 show tetravalency by sharing four of its valence electrons. Therefore, they have oxidation state of +4. In addition, Ge, Sn and Pb also show +2 oxidation state.
(4) Catenation: Catenation is ability of like atoms to link with one another through covalent bonds. Tendency decreases from C to Pb. It is due to the decreasing M-M single bond energy. Thus, the tendency for catenation decreases as:
C > Si > Ge > Sn > Pb
(5) Allotropy: All the elements of the carbon family with the exception of lead exhibit allotropy. Carbon exists as two important allotropic forms diamond and graphite.
[B]. Chemical Properties
1. Reactivity towards air: All members of this group form monoxide of the general formula MO such as CO, SiO, SnO and PbO. All members of this group form dioxides of molecular formula MO2 such as CO2, SiO2, GeO2, SnO2 and PbO2.
2. Reactivity towards water: In this family three members i.e., carbon, silicon and germanium are affected by water while lead is not affected by water due to formation of protective oxide film but tin decomposes with steam into tin dioxide and hydrogen gas.
3. Reactivity towards halogen: These elements form two types of hallides – MX2 and MX4. Most of the MX4 are covalent. SnF4 and PbF4 are ionic in nature.
Anomalous Behaviour of Carbon
Carbon shows anomalous behaviour due to its smaller size, higher electronegativity, higher ionization enthalpy and unavailability of d orbitals. Carbon atom forms double or triple bonds involving pπ-pπ bonding. Carbon has also the property to form closed chain compounds with O, S and N atoms as well as forming pπ-pπ multiple bonds with other elements particularly N, S and O. When we move down the group size increases and electronegativity decreases hence catenation tendency decreases. Order is
C >> Si > Ge ≈ S
Allotropes of Carbon
Carbon shows allotropism due to catenation and pπ-pπ bond formation. Carbon exists in two allotropic forms – crystalline and amorphous. The crystalline forms are diamond and graphite while the amorphous forms are coal, charcoal and lamp-black. The third form is fullerenes discovered by Kroto, Smalley and Curl.
Note: Tin has maximum number of allotropes.
Diamond
In diamond each carbon is joined to other four carbon tetrahedrally and carbon-carbon bond length is 1.54Å and bond angle is 109º28′ having sp3 hybridisation on each carbon. All four electrons in carbon are involved in bonding hence, it is bad conductor of electricity. Diamond is an excellent thermal conductor.
It is hardest natural substance known. It is transparent and has a specific gravity 3.52 and its refractive index is high (2.45). Difficult to break due to extented covalent bonding. Diamond is used for making cutters. Blades of diamond are used in eye surgery and as an abrasive for sharpening hard tools. Impure diamonds (black) are used in knives for cutting glass.
Graphite
Each carbon is sp2 hybridised. It has layered structure. These layers are attracted by van der Waals force. Each carbon has one free electron in p-orbital, so it is a good conductor of electricity. All electrons get delocalized in one layer and form π-bond. Electron jumps from one orbital to another hence it is a good conductor of heat and electricity. In graphite carbon-carbon bond length is 141.5 pm and distance between adjacent graphite layer is 340 pm.
Graphite is used as a lubricant at high temperature. Oil gets burn or denatured at high temperature but graphite does not get denatured even at high temperature so, preferred over oil and grease.
Fullerene
It was made as a result of action of a laser beam or strong heating of a sample of graphite in presence of inert atmosphere. The sooty material mainly contains C60 with C70 (small amount). Most common fullerene is C60 called Buckminsterfullerene which has football-like structure. It contains 20 six-membered ring and 12 five-membered ring. It is used to make ball bearings.
Coal
It is the crude form of carbon. It has been formed in nature as a result of slow decomposition of vegetable matter under the influence of heat, pessure and limited supply of air. The successive stages of transformation are : peat, lignite, bituminous, steam coal and anthracite. Bituminous is hard stone, burns with smoky flame. The superior quality is anthracite which burns with non-smoky flame.
Uses of carbon
Graphite: In making lead pencils, electrodes of electric furnances, as a moderator in nuclear reactor, as a lubricant in machinery.
Charcol: In removing offensive odour from air, in removing fused oil from crude spirit, in decolourising sugar syrup, in gas masks etc.
Carbon black: For making printing inks, black paints, Indian inks, boot polishes and ribbons of typewriters.
Coal: For the manufacture of coal gas, coal tar, coke and synthetic petrol.
Compounds of Carbon
(1) Carbon Monoxide (CO)
Preparation: Carbon monoxide is majorly prepared by
2C + O2 ⟶ 2CO
Properties:
(i) Burns with blue flame2CO + O2 ⟶ 2CO2
(ii) CO + Cl2 ⟶ COCl2 (Phosgene)
(iii) CO + 2H2 ⟶ CH3OH
(iv) Many of the transition metals form metal carbonylsNi + 4CO ⟶ Ni(CO)4
(2) Carbon Dioxide (CO2)
Preparation: Carbon dioxide is mostly prepared by decomposition of carbonates and bicarbonates
(i) CaCO3 + 2HCl ⟶ CaCl2 + H2O + CO2
(ii) CaCO3 ⟶ CaO + CO2
Properties: Carbon dioxide is an acidic, colourless gas. The important properties are:
The s-block elements of the Periodic Table are those in which the last electron enters the outermost s-orbital. As the s-orbital can accommodate only two electrons, two groups (1 & 2) belong to the s-block of the Periodic Table.
Group-1 of periodic table contains : Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs) and Francium (Fr). Together these elements are called alkali metals because they form hydroxides on reaction with water, which are strongly alkaline in nature.
The group-2 includes Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba) and Radium (Ra). Except Beryllium, rest of the elements of group-2 are called the alkaline earth metals. These are called so because their oxides and hydroxides are alkaline in nature and these metal oxides are found in the earth crust.
Group-1 Elements : Alkali Metals
1. Electronic Configuration
Electronic Configuration of elements of group-1 is ns1, where n represents the valence shell. The alkali metals have one valence electron, outside the noble gas core.
2. Atomic and ionic radii
The atoms of alkali metals have the largest size in their respective periods. The atomic radius increases on moving down the group because on moving down the group there is a progressive addition of new energy shells.
3. Ionization enthalpy
The ionization enthalpies of the alkali metals are generally low and decrease down the group from Li to Cs. This is because on moving down the group is due to increase in size of the atoms of alkali metals and increase in the magnitude of screening effect.
4. Hydration enthalpy
The alkali metal ions are extensively hydrated in aqueous solutions. The hydration enthalpies of alkali metal ions decrease with increase in ionic size Li+ > Na+ > K+ > Rb+ > Cs+.
5. Physical properties
Alkali metals are silvery white in colour and are generally soft and light metals.
The densities of alkali metals are low and increase down the group.Alkali metals have low melting and boiling point.
When alkali are heated metals they impart characteristic colours to the flame.
When the excited electron comes back to the ground state, there is emission of radiation in the visible region.
6. Chemical Properties
The alkali metals are highly reactive elements. The cause for their high chemical reactivity is
(i) Low value of first ionisation enthalpy
(ii) Large size
(iii) low heat of atomisation.
(i). Reaction with Air: Alkali metals burn very fast in oxygen and form different kind of oxides like monoxides, peroxides and superoxides. In all the compounds formed by alkali metals with oxygen, their oxidation state is +1.
4Li + O2 ⟶ 2Li2O (Oxide)
Na + O2 ⟶ Na2O2 (Peroxide)
M + O2 ⟶ MO2 (Superoxide)
(ii). Reaction with Water: The alkali metals on reaction with water form their respective hydroxide and dihydrogen.
2M + 2H2O ⟶ 2M+ + 2OH– + H2
(M = an alkali metal)
(iii). Reaction with Dihydrogen: Alkali metal react with dry di-hydrogen at about 673 K (lithium at 1073 K) to form crystalline hydrides which are ionic in nature and have high melting points.
2M + H2 ⟶ 2M+H–
(iv). Reaction with Halogens: The alkali metals react vigorously with halogens and form halides which are ionic in nature, M+X–. But the halides of lithium are a bit covalent in nature.
(v). Reaction with Mercury: The alkali metals have strong tendency to get oxidised, that is why they act as strong reducing agents, among these lithium is the strongest and sodium is the least powerful reducing agent.
(vi). Reducing Nature: Alkali metals combine with mercury to form amalgams. The reaction is highly exothermic in nature.
Na + Hg ⟶ Na[Hg]
(vii). Solutions in liquid Ammonia: All alkali metals dissolve in liquid ammonia and give deep blue colour solution which are conducting in nature. These solutions contain ammoniated cations and ammoniated electrons as shown below:
M + (x + y)NH3 ⟶ [M(NH3)x]+ + [e(NH3)y]–
Uses of Alkali Metals
Lithium is used as a metal in a number of alloys. Its alloys with aluminium to make aircraft parts.
Lithium hydroxides is used in the ventilation systems of space crafts and submarines to absorb carbondioxide.
Lithium aluminium hydride (LiAlH4) is a powerful reducing agent which is commonly used in organic synthesis.
Liquid sodium or its alloys with potassium is used as a coolant in nuclear reactors.
Sodium-lead alloy is used for the preparation of tetraethyl lead, Pb(C2H5)4, which is used as an antiknocking agent in petrol.
Sodium is used in the production of sodium vapour lamps.
Potassium chloride is used as fertilizer.
Potassium hydroxide is used in the manufacture of soft soaps and also as absorbent of carbon dioxide.
Potassium ions play a vital role in biological systems.
Caesium is used in photoelectric cells.
Anomalous Properties of Lithium
Lithium shows properties which are very different from the other members of its group. This is due to the
exceptionally small size of its atom and ion.
greater polarizing power of lithium ion.
as compared to other alkali metals, lithium is harder and its melting point and boiling point are higher.
among all the alkali metals lithium is least reactive but the strongest reducing agent.
Some important Compounds of Sodium
Sodium is highly reactive and always found in combined state. The isotope of sodium (Na) is used in detection of leukemia. The compound of sodium are given below:
1. Sodium Oxide (Na2O)
Preparation:
2NaNO2 + 6Na ⟶ 4Na2O + N2
Properties:
Sodium oxide is a colourless ionic solid.
Aqueous solution of sodium oxide is strongly basic.
Sodium oxide on reaction with liquid ammonia forms sodamide.
At low temperature, when sodium peroxide is reacted with water or acids, H2O2 is formed.
2. Sodium Peroxide (Na2O2)
Preparation:
Sodium when heated in excess of air or when heated in excess of pure oxygen gives sodium peroxide.
2Na + O2 ⟶ Na2O2
Properties:
Sodium peroxide is a pale yellow diamagnetic compound.
Sodium peroxide is a powerful oxidising agent.
Sodium peroxide combines with CO and CO2 to give carbonate.
At low temperature, when sodium peroxide is reacted with water or acids, H2O2 is formed.
Na2O2 + 2H2O ⟶ 2NaOH + H2O2
3. Sodium Hydroxide (Caustic Soda) (NaOH)
Preparation:
When sodium carbonate is treated with calcium hydroxide it give calcium carbonate along with sodium hydroxide. Also known as lime caustic soda process. It is a reversible reaction.
Na2CO3 + Ca(OH)2 ⟶ 2NaOH + CaCO3
Properties
Sodium hydroxide is a white crystalline deliquescent solid.
Sodium hydroxide is corrosive in nature.
Sodium hydroxide is highly soluble in water.
Sodium hydroxide reacts with acid forming corresponding salts.
NaOH + HCl ⟶ NaCl + H2O
Uses: It is used in
the manufacture of soap, paper, artificial silk and a number of chemicals,
in petroleum refining,
in the purification of bauxite,
in the textile industries for mercerising cotton fabrics,
for the preparation of pure fats and oils, and
as a laboratory reagent.
4. Sodium Carbonate (Na2CO3)
Preparation:
NH3 + H2O + CO2 ⟶ NH4HCO3
NaCl + NH4HCO3 ⟶ NaHCO3 + NH4Cl
2NaHCO3 ⟶ Na2CO3 + H2O + CO2
Properties:
Sodium carbonate is a white crystalline solid.
Na2CO3.10H2O is known as washing soda.
Sodium carbonate reacts with acids to give carbon dioxide.
Uses:
It is used in water softening, laundering and cleaning.
It is used in the manufacture of glass, soap, borax and caustic soda.
It is used in paper, paints and textile industries.
It is an important laboratory reagent both in qualitative and quantitative analysis.
Na2CO3 + HCl ⟶ NaCl + H2O + CO2
Properties:
On heating sodium bicarbonate loses CO2 and H2O forming Na2CO3.
2NaHCO3 ⟶ Na2CO3 + H2O + CO2
6. Sodium Chloride (NaCl)
Manufacture of sodium chloride is done from sea water. Sea water is allowed to dry up under summer heat in small tanks and solid crust so formed is collected.
Properties:
Sodium chloride is a white crystalline solid.
It is slightly hygroscopic.
It is soluble in water and insoluble in alcohol.
Uses:
It is used as a common salt or table salt for domestic purpose.
It is used for the preparation of Na2O2, NaOH and Na2CO3.
5. Sodium Bicarbonate (Baking Soda) (NaHCO3)
Preparation:
When NaOH is treated with CO2 in presence of H2O it gives sodium bicarbonate.
NaOH + CO2 + H2O ⟶ NaHCO3
Properties:
On heating sodium bicarbonate loses CO2 and H2O forming Na2CO3.
2NaHCO3 ⟶ Na2CO3 + H2O + CO2
Group-2 Elements : Alkaline Earth Metals
The elements of group-2 are Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba) and Radium (Ra). Except for Be, rest are known as alkaline earth metals, because they were alkaline in nature and existed in the earth.
1. Electronic Configuration
The alkaline earth metals have 2 electrons in the s-orbital of the valence shell. Their general electroni configuration [Noble gas]ns2
2. Atomic and Ionic Radii
The atomic radii as well as ionic radii of the members of the family are smaller than the corresponding members of alkali metals. Within the group, the atomic and ionic radii increase with increase in atomic number.
3. Ionization Enthalpies
The alkaline earth metals owing to their large size of atoms have fairly low values of ionization enthalpies. Within the group, the ionization enthalpy decreases as the atomic number increases.
4. Hydration Enthalpies
The hydration enthalpies of alkaline earth metal ions are larger than those of alkali metal ions. Therefore, compounds of alkaline earth metals are more extensively hydrated, for example, magnesium chloride and calcium chloride exist. the hydration enthalpies of alkaline earth metal ions decrease with increase in ionic size down the group. Be2+ > Mg2+ > Ca2+ > Sr2+ > Ba2+
5. Physical Properties
The alkaline earth metals are silvery white, lustrous and relatively soft but harder than the alkali metals.The melting and boiling points of these metals are higher than the corresponding alkali metals.The electropositive character increases down the group from Be to Ba.Calcium, strontium and barium impart characteristic brick red, crimson and apple green colours respectively to the flame.Th alkaline earth metals just like those of alkali metals have high electrical and thermal conductivities.
6. Chemical Properties
As compared to alkali metals, alkaline earth metals are less reactive due to their relatively higher ionization enthalpies. The reactivity of alkaline earth metals increases on going down the group.
(i). Reaction with water: Ca Sr, and Ba have reduction potentials similar to those of corresponding group Ist metals and are quite high in the electrochemical series. They react with cold water readily, liberating hydrogen forming metal hydroxides.
Ca + 2H2O ⟶ Ca(OH)2 + H2
(ii). Reaction with Air: Except Be these metals are easily tarnished in air as a layer of oxide is formed on their surface. Ba in powdered form bursts into flame on exposure to air.
(iii). Reaction with hydrogen: The elements Mg, Ca, Sr and Ba all react with hydrogen to form hydrides MH2.
(iv). Reaction with oxygen: Except Ba and Ra the elements when burnt in oxygen form oxides of the type MO.
(v). Reaction with halogens: When heated with halogens the alkaline earth metals directly combine with them and form the halides of the type MX2.
Ca + Cl2 ⟶ CaCl2
(vi). Reaction with acids: The alkaline earth metals readily react with acids liberating dihydrogen.
M + 2HCl ⟶ MCl2 + H2
Uses of alkaline earth metals
Beryllium is used in the manufacture of alloys. Cooper-Beryllium alloys are used in the making of high strength springs.
Metallic beryllium is used for making windows of X-rays tubes.
Magnesium, being a light metal, forms many light alloys with aluminum, zinc, manganese and tin.
Magnesium is used in flash powders and bulbs, incendiary bombs and signals.
Magnesium-aluminium alloys are used in aircraft construction.
Magnesium is used as sacrificial anode for the prevention of corrosion of iron.
A suspension of magnesium hydroxide in water (called milk of magnesia) is used as an ant-acid to control excess acidity in stomach.
Magnesium carbonate is an ingredient of tooth-paste.
Calcium is used in the extraction of metals from oxides which are difficult to reduce with carbon.
Calcium and barium metals are used to remove air from vacuum tubes, due to their tendency to react with oxygen and nitrogen at high temperature.
Radium salts are used for radio therapy of cancer.
Anomalous Behaviour of Beryllium
Beryllium shows different behaviour from the rest members of its group and shows diagonal relationship to aluminium due to reasons discussed below.
Beryllium has exceptionally small atomic and ionic sizes and therefore does not compare well with other members of the group, because of high ionisation enthalpy and small size it forms compounds which are largely covalent and get easily hydrolysed.
Beryllium does not exhibit coordination number more than four as in its valence shell, there are only four orbitals. The remaining members of the group can have a coordination number of six by making use of d-orbitals.
The oxides and hydroxide of beryllium unlike the hydroxide of other elements in the group, are amphoteric in nature.
Compounds of Calcium
1. Calcium Oxide (CaO)
Preparation:
Calcium carbonate when decomposed at 800°C gives calcium oxide.
CaCO3 ⟶ CaO + CO2
Properties:
Calcium oxide is also known as ‘Quick lime’ or ‘Burnt lime’, is white amorphous substance.
When water is added to lime a hissing sound is produced along with clouds of steam. The lime forms slaked lime [Ca(OH)2].
Calcium oxide reacts with moist chlorine to form bleaching powder. CaO + Cl2 ⟶ CaOCl2
Calcium oxide on reaction with moist HCl gas forms CaCl2.CaO + 2HCl ⟶ CaCl2 + H2O
2. Calcium Carbonate (CaCO3)
Preparation:
Carbon dioxide when passed through lime water gives calcium carbonate.
Ca(OH)2 + CO2 ⟶ CaCO3 + H2O
Properties:
Calcium carbonate is a white powder insoluble in water.
Calcium carbonate dissolves in water in presence of CO2 due to formation of calcium bicarbonate.
CaCO3 + H2O + CO2 ⟶ Ca(HCO3)2
3. Calcium Chloride (CaCl2)
Preparation:
Calcium oxide, calcium hydroxide or calcium carbonate when treated with HCl gives calcium chloride.
CaO + 2HCl ⟶ CaCl2 + H2O
Properties:
Calcium chloride is a colourless deliquescent crystalline substance which is soluble in water as well as in alcohol.
Crystals of calcium chloride when strongly heated gives off water of crystalisation.
4. Calcium sulphate (Plaster of Paris)
Preparation:
When Gypsum is heated at about 120° – 130°C, Plaster of Paris is formed.
2CaSO4 + 4H2O ⟶ (CaSO4)2H2O + 3H2O
Properties:
It is a white crystalline solid. It is sparingly soluble in water.
It becomes anhydrous at about 200°C. Anhydrous form is known as dead burnt plaster.
5. Calcium hydroxide Ca(OH)2
Preparation:
CaO + H2O ⟶ Ca(OH)2
Properties:
1. It gives CaCO3 and Ca(HCO3)2 with CO2
Ca(OH)2 + CO2 ⟶ CaCO3 + H2O
2. On prolong treatment with CO2 milkiness disappears due to formation of Ca(HCO3)2
CaCO3 + H2O + CO2 ⟶ Ca(HCO3)2
Summary
s-block elements : The elements in which last electron enters into s-orbital are called s-block elements.
Alkali metals : The elements of group 1 whose hydroxide are strong alkali.
Alkaline earth metal : The elements of group 2, and their oxides and hydroxides are alkaline in nature and their oxides are found in the Earth’s crust.
Diagonal relationship : The resemblance in properties of elements of second period with elements of third period present diagonally on the right hand side.
Monovalent sodium and potassium ions and divalent magnesium and calcium ions are found in large proportions in biological fluids. These ions perform important biological functions such as maintenance of ion balance and nerve impulse conduction.
