CBSE Class 10 Science 2020 · Paper 31/4/1 · Question 17

Carbon forms about three million compounds because of catenation (its atoms bond to one another in long chains, branched chains and rings) and tetravalency (each atom forms four covalent bonds, with carbon or with other elements). The other members of group 14 do not show this property. The explanation: (1) Carbon, the first member of the group, has the smallest atom, and the force of attraction between its atoms is the highest. (2) Carbon has four valence electrons and needs four more to attain a stable configuration, which it gets by sharing, forming four covalent bonds. Silicon, germanium, tin and lead also have four valence electrons, so this alone does not set carbon apart; its small size and strong bonds do, as (1), (3) and (4) show. (3) Because of its small size, the nucleus of carbon holds the shared pairs of electrons strongly, so its bonds are strong and its compounds stable. (4) The other elements of the group have bigger atoms, so the bonds they form are much weaker; silicon, for example, forms chains of only up to seven or eight atoms, and these are very reactive.