Why does carbon neither form `C^(4+)` cation nor `C^(4-)` anion, but forms covalent compounds?

Explanation

i. The electronic configuration of carbon is (2, 4). It has four electrons in its valence shell.
ii. It could form `C^(4+)` cation to attain the stable duplet configuration of noble gas helium (He) by losing one after another all th efour valence electrons. However, the net positive charge on the carbon atom goes on increasing during loss of every electron and hence, to lose the next electron would require higher energy making the task more difficult. Also, the `C^(4+)` cation formed in the process is extremely unstable in spite of having stable noble gas configuration because it has small size and high net positive charge.
iii. It could form `C^(4-)` anion to attain the stable configuration of noble gas neon (Ne) be gaining one after another four electrons in its valence shell. However, the net negative charge on the carbon atom goes on increasing during addition of every new electron and hence, to gain the next electron would require higher energy to overcome the increased repulsive force making the task more difficult. Also, it would be difficult for the nucleus of `C^(4-)` anion having six protons to hold on to ten electrons around it.
Hence, carbon atom forms covalent compounds by sharing valence electrons between either the atoms of carbon or atoms of other elements to attain the noble gas configuration of neon.