Chemical bond valence shell electron-pair repulsion

Valence The highest-energy electrons in an atom, which an atom loses, gains, or shares in forming a chemical bond. Valence shell electron-pair repulsion (VSEPR) A procedure based on electron repulsion in molecules that enables chemists to predict approximate bond angles. 

Chemical bonding— valence-shell electron-pair repulsion theory. 

The most stable shape for any molecule maximizes electron-nuclear attractive interactions while minimizing nuclear-nuclear and electron-electron repulsions. The distribution of electron density in each chemical bond is the result of attractions between the electrons and the nuclei. The distribution of chemical bonds relative to one another, on the other hand, is dictated by electrical repulsion between electrons in different bonds. The spatial arrangement of bonds must minimize electron-electron repulsion. This is accomplished by keeping chemical bonds as far apart as possible. The principle of minimizing electron-electron repulsion is called valence shell electron pair repulsion, usually abbreviated VSEPR. 

Once computed on a 3D grid from a given ab initio wave function, the ELF function can be partitioned into an intuitive chemical scheme [30], Indeed, core regions, denoted C(X), can be determined for any atom, as well as valence regions associated to lone pairs, denoted V(X), and to chemical bonds (V(X,Y)). These ELF regions, the so-called basins (denoted 2), match closely the domains of Gillespie s VSEPR (Valence Shell Electron Pair Repulsion) model. Details about the ELF function and its applications can be found in a recent review paper [31],... 

We now turn from the use of quantum mechanics and its description of the atom to an elementary description of molecules. Although most of the discussion of bonding in this book uses the molecular orbital approach to chemical bonding, simpler methods that provide approximate pictures of the overall shapes and polarities of molecules are also very useful. This chapter provides an overview of Lewis dot structures, valence shell electron pair repulsion (VSEPR), and related topics. The molecular orbital descriptions of some of the same molecules are presented in Chapter 5 and later chapters, but the ideas of this chapter provide a starting point for that more modem treatment. General chemistry texts include discussions of most of these topics this chapter provides a review for those who have not used them recently. 

Theory is a term that is very widely used by chemists. To take the area of chemical bonding as an example, chemists widely refer to molecular orbital (hereafter MO) theory, valence bond (VB) theory, hybridization theory, valence shell electron pair repulsion (VSEPR) theory, and ligand field theory. And even those probably do not exhaust the list. 

In everyday practice, chemists often use a minimal model of molecules that enables them to compare the geometry and vibrational frequencies with experiment to the accuracy of about 0.01 A for bond lengths and about 1 for bond angles. This model assumes that the speed of light is infinite (non-relativistic effects only), the Born-Oppenheimer approximation is valid (i.e., the molecule has a 3-D structure), the nuclei are boimd by chemical bonds and vibrate in a harmonic way, the molecule moves (translation) and rotates as a whole in space. In many cases, we can successfully predict the 3-D structure of a molecule by using a very simple took the Valence Shell Electron Pair Repulsion (VSEPR) algorithm. 

Finally, in addition to simply representing a pair of shared electrons, a chemical bond has structural implications as well. Because electrons are negatively charged, when there are several distinct bonds, they will tend to be physically separated from each other. This idea is the basis for a method to predict the geometry of molecules called the Valence Shell Electron Pair Repulsion (VSEPR) theory. Using this theory, the general shape of molecules and ions can be predicted. 

Molecular Geometry Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule. For relatively small molecules, in which the central atom contains two to six bonds, geometries can be rehably predicted by the valence-shell electron-pair repulsion (VSEPR) model. This model is based on the assumption that chemical bonds and lone pairs tend to remain as far apart as possible to minimize repulsion. 

Presents in an unitary quantum theory the various aspects of chemical bonding, from classical description of valence bond and molecular orbital theories to the modem bondonic-bosonic picture of chemical field and interaction, to crystal and ligand field related with symmetry properties and eigen-groups of molecules, to Valence Shell Electron Pair Repulsion-VSEPR model ... 

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