Gillespie-Nyholm model

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. 

Gibson model, 38 174-176 Gillespie-Nyholm valence shell electron-pair repulsion theory, 18 325 Glass-formers , 4 294 Glauber s salt, 4 17... 

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)... 

Sidgwick and Powell were first to correlate the number of electron pairs in the valence shell of a central atom and its bond configuration [106], Then Gillespie and Nyholm introduced allowances for the difference between the effects of bonding pairs and lone pairs, and applied the model to large classes of inorganic compounds [107],... 

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... 

Molecular geometry is the general shape of a molecule as determined by the relative positions of the various atomic nuclei. A number of physical properties such as melting point, boiling point, density and a number of chemical properties are based on the molecular geometry. A very useful model to predict the general shape of a molecule was developed by Gillespie and Nyholm in 1957. The theory called the Valence Shell Electron Pair Repulsion (VSEPR pronounced as vesper) theory is an... 

In all of the above cases, the feometry is in afreement with the expectations of the valence shell electron pair repulsion (VSEPR) model of Gillespie and Nyholm [77]. The VSEPR model accounts for the molecular geometry in nearly all cases for main group elements in free molecules. Deviations are observed in solids because of the contribution from the lattice energy. For example, in SnO and red PbO, the coordination MO4E is square pyramidal, instead of seesaw expected by the VSEPR model [78,79]. 

VSEPR The valence shell electron pair repulsion model, originally introduced by Nyholm and Gillespie (with antecedents from Sidgwick and Powell), which assumes that molecular geometry associated with a central atom is determined by the number of groups (single bonds, double bonds, triple bonds, or lone pairs) surrounding that atom. 

The shapes of molecules containing a central p-block atom tend to be controlled by the number of electrons in the valence shell of the central atom. The valence-shell electron-pair repulsion (VSEPR) model provides a simple model for predicting the shapes of such species. The model combines original ideas of Sidgwick and Powell with extensions developed by Nyholm and Gillespie, and may be summarized as follows ... 

Eighteen years later (in 1957), the VSEPR model was further developed and its predictive power enhanced by R. J. Gillespie and R. S. Nyholm [63]. They interpreted the less-than-tetrahedral valence angles listed in Table 8 as evidence that the repulsion between a lone pair and a bond pair is greater than the repulsion between two bmid pairs. Since a bond pair is extended further into space than a lone pair, it is reasonable to assume that it requires less space in the valence shell of the central atom. The larger than tetrahedral valence angles in trimethylamine and dimethyl ether are presumably determined by steric repulsion between the methyl groups. 

One of the goals of the ELF approach is to provide an interpretative tool of quantum chemical calculations in terms of purely chemical concepts without the recourse to the nature of the approximate wave functions. The ELF recovers many features of the simple chemical models based on a spatial distribution of the valence electron, namely, the valence theory of G. N. Lewis, the mesomery concept of C. K. Ingold, and the VSEPR model of R. J. Gillespie and R. S. Nyholm. The partition of the electron density based on a statistical criterion provides a quantum mechanical support to the hypotheses which are explicitly or implicitly assumed in these models. Indeed, this statistical approach provides at least formally a mathematical bridge between quantum mechanics and chemistry which enables to critically think about the content and the definition of many chemical concepts related to the... 

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