Question

why carbon forms covalent compound

Answer 1

because it have 4 valency...so it can combine with...covelent bond...

Answer 2

Because carbon has 4 electrons in its outermost shell (and because each covalent bond requires a donation of 1 electron, per atom, to the bond) carbon has exactly fourbonds to make, and is only stable if all 4 of these bonds are used. This same rule applies to all of the atoms in the second row of the periodic table