Introduction
Carbon forms the largest number of compounds, next only to hydrogen. It ranks seventeenth in the order of abundance in the earth’s crust. Carbon occurs in the free native state as well as in the combined state. Carbon and its compounds are widely distributed in nature.
In its elemental form, carbon occurs in nature as diamond and graphite. Coal, charcoal and coke are impure forms of carbon. The latter two are obtained by heating wood and coal in the absence of air, respectively. In the combined state, carbon is present as carbonate in many minerals, such as hydrocarbons in natural gas, petroleum etc. In air, carbon dioxide is present in small quantities, (0.03%).
Our food also contains carbon in the combined form. All living systems contain carbon compounds. Indeed, life as we know today, would be impossible without such carbon compounds.
Carbon is a non-metallic element and the first member of group 4 of the periodic table
Allotropes of Carbon
The existence of one element in different forms, having different physical properties, but similar chemical properties is known as allotropy. Different forms of an element are called ‘allotropes’ or allotropic forms. Carbon shows allotropy. The various allotropic forms of carbon can be broadly classified into two classes.
- Crystalline form
Diamond and graphite are crystalline forms.
- Amorphous form
Coal, coke, charcoal (or wood charcoal), animal charcoal (or bone black), lamp black, carbon black, gas carbon and petroleum coke are amorphous forms.
Diamond
Diamonds are chiefly found in the Union of South Africa, the Belgian Congo, Brazil, British Guiana, India etc. Diamond was discovered for the first time in India. The famous ‘Kohinoor diamond’ (186 – carat) and the ‘Regent or Pitt’ (studded in Napoleon’s state sword, 136.2 carat) were found near Kistna river in South India. The ‘Cullinan diamond’, the largest ever found weighed 3025.75 carat (about 600 g) was mined in South Africa in 1905.
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