Question

Explain, giving reason, why carbon neither forms C⁴⁺ cations nor C⁴⁻ anions, but forms covalent compounds which are bad conductors of electricity and have low melting point and low boiling point. 

Answer 1

Carbon has four electrons in its outermost shell and needs to gain or lose four electrons to attain noble gas configuration. If it were to gain or lose electrons then its form C^4– anion and C⁴⁺ cation, respectively.

It could gain four electrons forming C^4– anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons.

It could lose four electrons forming C⁴⁺ cation. But it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding on to just two electrons.

Hence, carbon neither forms C⁴⁺ cations nor C⁴⁻ anions.

Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements. Such bonds which are formed by the sharing of an electron pair between two atoms are known as covalent bonds. Covalently bonded molecules are seen to have strong bonds within the molecule, but inter-molecular forces are small. This gives rise to the low melting and boiling points of these compounds. Since the electrons are shared between atoms and no charged particles are formed, such covalent compounds are generally poor conductors of electricity.