Question

Are the number of lone pairs of electrons on the central atoms the main factor that's used to determine the molecular shape or geometry?

Answer 1

The shapes of the molecules is determined mainly by the electrons surrounding the central atom. Therefore, VSEPR theory gives simple directions on how to predict the shape of the molecules. The basic principle of the VSEPR theory is that molecular geometry can be predicted based on the notion that electron pairs in molecules tend to repel each other and achieve a maximum separation from each other. This applies both to bonding electrons as well as lone pairs.

lone pair -lone pair repulsion > lone pair - bond pair repulsion > bond pair -bond pair repulsion

Thus, in order to determine the shape of the molecule, we must remember to minimize the repulsion in the order mentioned above.