Valence-shell electron-pair repulsion VSEPR rule

For xenon fluorides and oxides, for example, the same models can be apphed as for interhalogen and halogen oxy species. Furthermore, the very successful valence shell electron pair repulsion (VSEPR) rules for molecule and ion shapes are as effective for noble gas compounds and their relatives as for classical octet compounds. 

Once we complete the grand construction of the molecular worlds, I will move on to discuss the 3D structure of molecules, using the famous valence shell electron pair repulsion (VSEPR) rules. 

The valence-shell electron-pair repulsion (VSEPR) rule states that aU groups emanating from an atom—whether single, double, or triple bonds, or lone pairs— wiU be in spatial positions that are as far apart from one another as possible. The VSEPR method does not consider singly occupied orbitals to be groups (see below for the reason). VSEPR is purely a theory based upon the notion that the electrostatic repulsions between entities consisting of two or more electrons dictate molecular geometries. 

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)... 

In this chapter a few simple rules for predicting molecular structures will be investigated. We shall examine first the valence shell electron pair repulsion (VSEPR) model, and then a purely molecular orbital treatment. 

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. 

We can predict the geometry of simple molecules using valence-shell electron-pair repulsion (VSEPR) theory. This theory is based on the idea that bonded and nonbonded electron pairs around a central atom repel one another. Hence, they are arranged in a geometry that provides maximum separation in space, and therefore rninimum electron repulsion. For bonds to carbon, the following rules apply ... 

One can see from Equation (4.10) that hybrid p-character (and associated X hybridization parameter) strongly affects hybrid direction and molecular shape. But what affects hybrid p-character The answer to this question gives one of the deepest insights into molecular shape, and is expressed in simple and intuitive terms by Bent s rule (cf. FcfeB, p. 13 8ff), the deeper principle that underlies success of the valence shell electron pair repulsions (VSEPR) model (Sidebar 4.3). 

The Lewis structures encountered in Chapter 2 are two-dimensional representations of the links between atoms—their connectivity—and except in the simplest cases do not depict the arrangement of atoms in space. The valence-shell electron-pair repulsion model (VSEPR model) extends Lewis s theory of bonding to account for molecular shapes by adding rules that account for bond angles. The model starts from the idea that because electrons repel one another, the shapes of simple molecules correspond to arrangements in which pairs of bonding electrons lie as far apart as possible. Specifically ... 

Some simple rules were supported by empirial evidence, valence shell electron pair repulsion model (VSEPR) and MO calculations, both semiempirical and ab initio. These rules could explain those features of molecular geometry which have been characterized by structural investigations using spectroscopic and diffraction techniques. 

The geometric structure of the covalent binary halides, whether neutral or complexed ions, can be explained on the basis of the Nyhotm-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... 

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