State the reason why carbon can neither form C4+ cations nor C4- anions but forms covalent compounds:
Atomic number of carbon is six. This means, that it has four electrons in its outermost shell and it needs four more electrons to attain noble gas electronic configuration. It does not form C4+ cations, as the removal of four valence electrons will require a huge amount of energy. The cation formed will have six protons and two electrons. This makes
it highly unstable. Carbon is unable to form C4- anion as its nucleus with six protons will not be able to hold ten electrons. Thus carbon achieves noble gas electronic configuration by sharing its four electrons with other elements, i.e. it forms covalent compounds.
(i) Covalent compounds are bad conductors of electricity due to lack of free electrons.
(ii) Covalent compounds are formed by covalent bonds and it has been found that the intermolecular forces of attraction in covalent compounds are weak. Thus, their melting and boiling points are quite low.