CBSE Class 10 Science 2022 · Paper 31/6/3 · Question 2

Carbon (atomic number $6$, configuration $2,4$) has 4 valence electrons and needs 4 more to attain a noble gas configuration (an octet). It could gain 4 electrons to form ${\text{C}}^{4-}$, but it would be difficult for a nucleus with only 6 protons to hold 10 electrons; or it could lose 4 electrons to form ${\text{C}}^{4+}$, but that needs a large amount of energy. So carbon does not readily form ions. Instead it shares its 4 valence electrons with other atoms (of carbon or of other elements), so that each atom attains a noble gas configuration; bonds formed by sharing electrons are covalent bonds, as in methane, ${\text{CH}}_4$. Hence carbon forms its compounds mainly by covalent bonding.