A theory for predicting the shapes of molecules. It postulates that the shapes of molecules are mostly determined by the repulsions between pairs of valence electrons, including lone pairs. The shapes predicted are: linear for two pairs; trigonal planar for three pairs; tetrahedral for four pairs; trigonal pyramidal for five pairs; and octahedral for six pairs. VSEPR is not applicable to molecules with d electrons but there is a modification of the theory that can be used with such molecules; this is known as the Kepert model, after D. L. Kepert who devised it in 1982. The successes of VSEPR theory have been rationalized in terms of the quantum mechanics of electrons in crystals.