We are surrounded by compounds made up of carbon and its

substituents. The list given below illustrates the importance of

carbon compounds in our daily life.

1. Foods [starch, sugar, fats, vitamins, proteins]

2. Fuels [wood, coal, alcohol, petrol]

3. Household and commercial articles [paper, soap, cosmetics,

oils, paints]

4. Textile fabrics [cotton, wool, silk, linen, rayon, nylon]

5. Drugs and disinfectants [penicillin, quinine, aspirin, sulfa

drugs]

6. Poisons [opium, strychnine]

7. Perfumes [vanillin, camphor]

8. Explosives [nitroglycerine, dynamite, picric acid, TNT]

9. Dyes [indigo, congo red, malachite green]

10. War gases [mustard gas, chloropicrin, lewisite]

Carbon is the 15th most abundant element in the Earth's crust,

and the fourth most abundant element in the universe by mass

after hydrogen, helium, and oxygen. It is present in all known

life forms, and in the human body carbon is the second most

abundant element by mass (about 18.5%) after oxygen.

This abundance, together with the unique diversity of organic

compounds and their unusual polymer-forming ability at the

temperatures commonly encountered on Earth, make this

element the chemical basis of all known life.

Carbon is the chemical element with symbol C and atomic

number 6. The electronic configuration of carbon atom is [He]

2s2 2p2. So valence shell (outermost shell) of carbon atom

contains 4 electrons.

According to Octate rule, Valence shell should have 8

electrons. So in order to complete octate either carbon will

accept 4 electrons or will loss 4 electrons.

C + 4e- C4- ……….(1)

C C4+ + 4e- ……….(2)

But this two are not possible. Carbon’s valence shell already

contain 4 electrons and because of small size of carbon if we

add another 4 electrons, there will be electronic – electronic

repulsion that won’t allow carbon to accept 4 electrons. So

this process is not possible.

In another process carbon losses 4 electrons. As we know,

size of carbon is small and it contains 4 electrons in its

valence shell, therefore attraction force between nucleus and

electrons won’t allow carbon to loss 4 electrons.

Carbon overcomes this problem by sharing its valence

electrons with other atom of carbon or with atoms of other

elements through covalent bonding.

Self combination or Catenation- Catenation is the

linkage of atoms of the same element into longer chains.

Catenation occurs most readily in carbon, which

forms covalent bonds with other carbon atoms to form longer

chains and structures. Carbon exhibits catenation to

maximum extent because of strong carbon-carbon bond and

tetracovalency.

Occurrence of Carbon- Carbon exists in two states in

nature.

Free state- Compound containing only carbon atom, not any

other element.

For eg.- Graphite, Diamond, Fullerene

Combined state- Carbon combine with other element to form

compound.

For eg.- CO2, C8H18 (Octane), C12H22O11(Sugar), MgCO3,

CaCO3

Allotropes of carbon - An element, in different forms,

having different physical properties but similar chemical

properties is known as allotropy. Carbon shows allotropy.

Such different forms are called 'allotrope' of an element or

allotropic forms.

There are three well known allotropic forms of carbon and

they are amorphous carbon, diamond and graphite. The fourth

allotropic form of carbon is buckminsterfullerenes which is

basically an artificial form of carbon and is made up of 60 C

atoms.

A few examples of pure carbons are as follows:

Coal, Coke, Charcoal (or wood charcoal), Animal Charcoal (or

bone black), Lamp black, Carbon black, Gas carbon and

Petroleum coke.

In diamond, each carbon atom is bonded to four other carbon

atoms forming a rigid three-dimensional structure.

In graphite, each carbon atom is bonded to three other carbon

atoms in the same plane giving a hexagonal array. One of these

bonds is a double-bond, and thus the valency of carbon is

satisfied. Graphite structure is formed by the hexagonal arrays

being placed in layers one above the other.

These two different structures result in diamond and graphite

having very different physical properties even though their

chemical properties are the same. Diamond is the hardest

substance known while graphite is smooth and slippery.

Graphite is also a very good conductor of electricity unlike

other non-metals.

Diamonds can be synthesised by subjecting pure carbon to

very high pressure and temperature. These synthetic

diamonds are small but are otherwise indistinguishable from

natural diamonds.

Diamond Graphite

It occurs naturally in free state.It occurs naturally and is manufactured

artificially.

It is the hardest natural substance

known.It is soft and greasy to touch.

It has high relative density (about 3.5). Its relative density is 2.3.

It is transparent and has high

refractive index (2.45).It is black in color and opaque.

It is non-conductor of heat and

electricity.

Graphite is a good conductor of heat

and electricity.

It burns in air at 900°C to give CO2. It burns in air at 700-800°C to give CO2.

It occurs as octahedral crystals. It occurs as hexagonal crystals.

It is insoluble in all solvents. It is insoluble in all ordinary solvents

Comparison of the Properties of Diamond and Graphite

Fullerenes form another class of carbon allotropes. The

first one to be identified was C-60 which has carbon

atoms arranged in the shape of a football. Since this

looked like the geodesic dome designed by the US

architect Buckminster Fuller, the molecule was named

fullerene.