Why do covalent moleucles have definite geometery?

In a covalent molecule, the central atom is surrounded by two types of electron pairs i.e. bond pairs (shared pair of electrons) and lone pairs (pairs not taking part in bond formation). The stability of the molecule demands that it should have minimum enthalpy. If the electron pairs (bond pairs or lone pairs) surrounding the central atom are nearer, they will repel each other, thereby increasing the enthalpy of the molecule. On the other hand, if the electron pairs are far apart, the repulsions between them will be less and so the enthalpy of the molecule will be low. Thus, the electron pairs surrounding the central atom will try to remain as far apart as possible.
As a result:
(i) All bonded atoms occupy such positions (around the central atom) in space where the repulsive forces between them are minimum.
(ii) The molecule attains minimum enthalpy and maximum stability.So molecule has a definite shape or geometry.