VSEPR theory proposes that the geometric arrangement of terminal atoms, or groups of atoms about a central atom in a covalent compound, or charged ion, is determined solely by the repulsions between electron pairs present in the valence shell of the central atom.

by writing the Lewis structure for the molecule, the number of electron pairs around the central atom can be determined. The geometry of the molecule depends on the number of bonding groups (pairs of electrons) and nonbonding electrons on the central atom.