Gillespie-Nyholm VSEPR

The fundamental basis for the VSEPR model is provided by the Pauli principle and not by electrostatics. The fundamental assumption of the model is that the electron pairs in the valence shell of an atom keep as far apart as possible, in other words they appear to repel each other. Electrons exhibit this behavior as a consequence of the Pauli exclusion principle of same spin electrons and not primarily as a consequence of their electrostatic repulsion. The role of the Pauli principle was clearly stated in the first papers on the VSEPR model (Gillespie Nyholm, 1957 Gillespie Nyholm, 1958) but this role has sometimes been ignored and the model has been incorrectly presented in terms of electrostatics. 

According to the VSEPR, Gillespie-Nyholm mles, the triatomic iso- and heteropolyhalogen cations, X3, X Ya, XaV" and YXZ are expected to be of bent strac-... 

The major features of molecular geometry can be predicted on the basis of a quite simple principle—electron-pair repulsion. This principle is the essence of the valence-shell electron-pair repulsion (VSEPR) model, first suggested by N. V. Sidgwick and H. M. Powell in 1940. It was developed and expanded later by R. J. Gillespie and R. S. Nyholm. According to the VSEPR model, the valence electron pairs surrounding an atom repel one another. Consequently, the orbitals containing those electron pairs are oriented to be as far apart as possible. 

The most widely used qualitative model for the explanation of the shapes of molecules is the Valence Shell Electron Pair Repulsion (VSEPR) model of Gillespie and Nyholm (25). The orbital correlation diagrams of Walsh (26) are also used for simple systems for which the qualitative form of the MOs may be deduced from symmetry considerations. Attempts have been made to prove that these two approaches are equivalent (27). But this is impossible since Walsh s Rules refer explicitly to (and only have meaning within) the MO model while the VSEPR method does not refer to (is not confined by) any explicitly-stated model of molecular electronic structure. Thus, any proof that the two approaches are equivalent can only prove, at best, that the two are equivalent at the MO level i.e. that Walsh s Rules are contained in the VSEPR model. Of course, the transformation to localised orbitals of an MO determinant provides a convenient picture of VSEPR rules but the VSEPR method itself depends not on the independent-particle model but on the possibility of separating the total electronic structure of a molecule into more or less autonomous electron pairs which interact as separate entities (28). The localised MO description is merely the simplest such separation the general case is our Eq. (6)... 

Ronald S. Nyholm and Ronald J. Gillespie Valence shell electron pair repulsion (VSEPR) approach to structure... 

Valence shell electron pair repulsion theory (VSEPR) provides a method for predicting the shape of molecules, based on the electron pair electrostatic repulsion. It was described by Sidgwick and Powell" in 1940 and further developed by Gillespie and Nyholm in 1957. In spite of this method s very simple approach, based on Lewis electron-dot structures, the VSEPR method predicts shapes that compare favorably with those determined experimentally. However, this approach at best provides approximate shapes for molecules, not a complete picture of bonding. The most common method of determining the actual stmctures is X-ray diffraction, although electron diffraction, neutron diffraction, and many types of spectroscopy are also used. In Chapter 5, we will provide some of the molecular orbital arguments for the shapes of simple molecules. 

The geometric structure of the covalent binary halides, whether neutral or complexed ions, can be explained on the basis of the Nyholm-Gillespie rules known as the Valence Shell Electron Pair Repulsion Model (VSEPR) theory the geometrical arrangements of the bonds around an atom in a species depends on the total number of electron pairs in the valence shell of the central atom, including both bonding... 

Gillespie, Ronald J., and Ronald S. Nyholm. Inorganic Stereochemistry. Quarterly Reviews of the Chemical Society (London) 11 (1957) 339-80. This essay introduced Valence Shell Electron Pair Repulsion (VSEPR) theory to the chemical community. 

The VSEPR algorithm comes from Ronald Gillespie and Ronald Nyholm [RJ. Gillespie and R.S. Nyholm, Quart. Rev. Chem. Soc., 11, 339 (1957)]. 

The repulsion between charges is a general phenomenon for the forces determining the structure of compounds. Gillespie and Nyholm presented a very general rule for the influence of Coulomb interaction with the valence shell electron pair repulsion (VSEPR) theory. 

The rules are known in chemistry as the VSEPR rules, where VSEPR is the acronym of valence-shell electron-pair repulsion, and they were devised in 1957 by Gillespie and Nyholm, ] two young scientists—one English, Gillespie, and the other Australian, Nyholm—who were both students of Sir Christopher Ingold, one of the greatest British chemists in the post-Second World War era. 

---