Since carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other monovalent elements. In order to satisfy its tetravalency carbon can form double or triple bonds also with other C-atoms or with oxygen, nitrogen etc.
Reasons for carbon forming a large number of compounds are:
(i) Catenation: Carbon has the unique property or ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation. These compounds may have long chains of carbon, branched chains of carbon or even carbon atoms arranged in rings.
(ii) Tetravalency: Carbon has four valence electrons in its valence shell so the valency of carbon is four. Due to this valency, carbon is a tetravalent element and it has the capability of satisfying its tetravalent by sharing its electrons with some monovalent elements and forming covalent bonds.
(iii) Carbon exhibits catenation much more than any other element due to its smaller size which makes the C - C bonds strong while the bonds between any other element are comparatively weaker due to its large size.
