Give an explanation of why carbon can only form covalent compounds and cannot produce $C^{+4}$ cations and $C^{-4}$ anions. Why are covalent compounds are bad compounds, bad conductors of electricity, and have low melting and boiling points?

Carbon cannot form a $C^{+4}$ cation because removing 4 electrons require a large amount of energy. Furthermore, carbon cannot form $C^{-4}$ an anion as it would be difficult for its nucleus with 6 protons to hold onto 10 electrons. Therefore Carbon atoms share electrons and form covalent compounds.
The atomic number of carbon is six. so the electronic configuration of carbon is 2,4; hene it has four electrons in its valence cell. So it requires a lot of energy if it loses its four electrons $C^{+4}$
It cannot form $C^{-4}$ because carbon cannot form $C^{-4}$ an anion, as its nucleus with six electrons will not be able to hold ten electrons. Thus carbon achieves noble gas electronic configuration by sharing its electron with other atoms.

1. Due to the lack of electrons in covalent compounds, they are bad conductors of electricity.
2. The intermolecular force of attraction in covalent compounds is weak. So they have low melting and boiling point.