Teaching Molecular Geometry with the VSEPR Model

Molecular geometry can be discussed in terms of the VSEPR model at several levels of sophistication—from the empirical model to a more complete model based on the Pauli principle. It is recommended that for most first-year courses VSEPR is presented at the purely empirical level or in the form of the domain version. A more sophisticated version is discussed here, not only because it should be taught in more advanced courses, but because it is important that it is understood by instructors and textbook writers so that incorrect explanations of the VSEPR model are not given. The difficulties associated with the usual treatment of the VB and MO theories in connection with molecular geometry in beginning courses are discussed. It is recommended that the VB and MO theories should be presented only after the VSEPR model either in the general chemistry course or in a following course, particularly in the case of the MO theory, which is not really necessary for the first-year course. The Pauli principle and its importance as the fundamental basis of the VSEPR model should be presented in a higher-level course, such as a quantum mechanics or physical chemistry course, or an inorganic course, in which VSEPR has many applications, for example, in the discussion of noble gas and other high coordination number molecules.