Gillespie-Nyholm electron pair repulsion

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)... 

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

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 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. 

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 ... 

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