CBSE Class 10 Science 2022 · Paper 31/4/1 · Question 11(b)

(i) Carbon (2, 4) would have to lose four electrons to form ${\text{C}}^{4+}$. Removing four electrons would require a large amount of energy, and it would leave a cation with six protons in its nucleus holding on to just two electrons. (ii) To form ${\text{C}}^{4-}$, carbon would have to gain four electrons. It would be difficult for a nucleus with only six protons to hold on to ten electrons, that is, four extra electrons. Carbon overcomes this problem by sharing its four valence electrons with other atoms of carbon or with atoms of other elements, forming covalent bonds. The shared electrons belong to the outer shells of both atoms, so both attain a noble-gas configuration: in methane, ${\text{CH}}_4$, carbon shares one pair with each of four hydrogen atoms and so has eight electrons in its outermost shell, while each hydrogen has two.