Explain the 'unique nature of carbon atom' with reference to —

(a) 'Tetravalency' — of carbon
(b) 'Catenation' — leading to formation of single, double and triple bonds and straight chain, branched chain and cyclic compounds.

(a) Tetravalency of carbon atoms — Carbon has four valence electrons. It forms four covalent bonds by mutually sharing it's four electrons with other atoms. Carbon is hence tetravalent or exhibits tetravalency. [At. no. of C = 6; Elec. Config. = 2,4]

(b) Catenation — Carbon atoms possess a unique property to link together (self linking) to form very long chains. This property is known as catenation. Catenation is shown by other elements also but Carbon exhibits this property of the maximum extent. This is due to the greater strength of carbon-carbon bond and due to tetra-covalency of carbon.

1. Formation of single, double and triple covalent bonds — Carbon is tetravalent having a valency of four. In order to satisfy its valency, it forms single, double and triple covalent bonds by sharing one, two or three pairs of electrons respectively between two carbon atoms as well as with other atoms like oxygen, nitrogen and so on.

2. Formation of straight chain, branched chain and cyclic compounds — The combination of carbon atoms with each other gives rise to straight or branched or cyclic and closed chains.