Question

Covalent bonds are directional in nature. Explain?

Answer 1

In essence, the first covalent bond (a `sigma` bond) is formed when two atoms share electrons in between them from their electron clouds. They can only share these electrons by approaching each other, and they can only approach each other in a straight line because there are only two atoms.

Another perspective is that the first covalent bond formed (a `sigma` bond) between free atoms requires head-on overlap of atomic orbitals. This view does in fact require the atoms to approach each other in a straight line, or else the overlap won't be head-on:

Either way, forming the first covalent bond requires two free atoms to approach each other in a straight line, which is therefore directional.

Even if we discussed the second covalent bond made, which is a `pi` bond, that requires sidelong overlap, which is directional as well:

This is directional in the sense that the overlap requires the orbitals to remain aligned in the same manner (which they will) as the atoms approach each other, and that shall be accomplished as long as they approach each other in a straight line.