Covalent bonding valence shell electron pair repulsion

Of the 20th century s development of structural chemistry, we mention the discovery of the electron-pair covalent bond by Lewis [22] which remains a fundamental tenet. It is remembered in every line we have drawn to represent a linkage and is present in most models of molecular structure, such as, for example, the valence shell electron pair repulsion (VSEPR) model [23]. 

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... 

The variation can, however, be understood if it is assumed that repulsive interactions between the atoms or groups bonded to the nitrogen atom predominate over the valence-shell electron-pair repulsion. That repulsion between the substituents should dominate does not seem unreasonable, since the nitrogen atoms in these species are bonded to three or four atoms, all with a larger covalent radius than the nitrogen. 

The deviation from tetrahedral valence angles at the aluminum atoms in the three species under discussion is adequately explained by the valence-shell electron-pair repulsion theory. The very polar Al-X bonds should require less space than the more covalent Al—C bonds, and the difference should be most pronounced in the fluoride. 

Two theories go hand in hand in a discussion of covalent bonding. The valence shell electron pair repulsion (VSEPR) theory helps us to understand and predict the spatial arrangement of atoms in a polyatomic molecule or ion. It does not, however, explain hoav bonding occurs, ] ist where it occurs and where unshared pairs of valence shell electrons are directed. The valence bond (VB) theory describes how the bonding takes place, in terms of overlapping atomic orbitals. In this theory, the atomic orbitals discussed in Chapter 5 are often mixed, or hybridized, to form new orbitals with different spatial orientations. Used together, these two simple ideas enable us to understand the bonding, molecular shapes, and properties of a wide variety of polyatomic molecules and ions. 

The reason for this unusual geometry was the availability of only the stereochemically active electrons for bonding. Thus, a SO modification of the valence shell electron pair repulsion (VSERP) theory was suggested in [130]. Han et al. [129], however, claim that this modification should be applied with caution, since no non-linear II8F2 structure has been detected as a minimum at the HF level of theory. An important observation was made that the fluorides of element 118 will most probably be ionic rather than covalent, as in the case of Xe. This prediction might be useful for future gas-phase chromatography experiments. 

Background Covalent bonding occurs when atoms share valence electrons. In the Valence Shell Electron Pair Repulsion (VSEPR) theory, the way in which valence electrons of bonding atoms are positioned is the basis for predicting a molecule s shape. This method of visualizing shape is also based on the molecule s Lewis structure. 

Like Charges Repel It is the repulsion of the electrons in covalent bonds of the valence shell of a molecule that is central to the valence shell electron pair repulsion model for explaining molecular geometry. And, although it is not so obvious, this same factor underlies the explanations of molecular geometry that come from orbital hybridization because these repulsions are taken into account in calculating the orientations of the hybrid orbitals. 

VSEPR model (valence shell electron pair repulsion) (Section 1.16) A method of predicting the geometry at a covalently bonded atom by considering the optimum geometric separation between groups of bonding and non-bonding electrons around the atom... 

The theoretical basis for a molecule possessing a particular geometric shape is the concept that electron pairs, whether they are part of a covalent bond (as in a bonding pair) or not (as in a nonbonding pair), will repel each other. In methane, water, and all other molecules, this repulsion means that the electron pairs will get as far away from each other as they can get. The general name for this theory is the valence-shell electron-pair repulsion (VSEPR) theory. 

The character of a covalent bond, the main focus of this chapter, was identified by G.N. Lewis in 1916, before quantum mechanics was fully developed. Lewis s original theory was unable to account for the shapes adopted by molecules. The most elementary (but qualitatively quite successful) explanation of the shapes adopted by molecules is the valence-shell electron pair repulsion model (VSEPR model). In this model, which should be familiar from introductory chemistry courses, the shape of a molecule is ascribed to the repulsions between electron pairs in the valence shell. The purpose of this chapter is to extend these elementary arguments and to indicate some of the contributions that quantum theory has made to understanding why atoms form bonds and molecules adopt characteristic shapes. 

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