CBSE Class 10 Science 2017 · Paper 31/1/2/C · Question 9

Carbon has the configuration $2,4$, so it would have to gain or lose four electrons to attain a noble-gas configuration. (i) It does not form ${\text{C}}^{4-}$: gaining four electrons would leave $6$ protons holding $10$ electrons, and it would be difficult for the nucleus to hold on to the four extra electrons. (ii) It does not form ${\text{C}}^{4+}$: removing four electrons would need a large amount of energy, leaving $6$ protons holding only $2$ electrons. So carbon shares its four valence electrons with other atoms and forms covalent bonds. (iii) In such covalent compounds (for example methane) no ions are formed, so there are no charged particles to carry a current: they are bad conductors of electricity. The bonds within each molecule are strong but the forces between molecules are weak, so little energy is needed to separate the molecules: their melting and boiling points are low.