Bond Angles. VSEPR Concept

Equalization of different orbitals through hybridization resembles equalization of valences (oxidation states) of ligands, when they are coordinated to the same atom. Thus, NO and NO3 radicals entering a coordination sphere, convert into identical NO2 ligands. Closely related effects include the distribution of two negative charges 

of electron pairs total lone Molecular type Molecular shape Examples 

To summarize, VSEPR model has been remarkably successful in predicting the structures of main-group compounds, but the predictions remain qualitative. All attempts to quantify them were so far unsuccessfiil, as well as attempts to extend this approach to transition metals ( extended VSEPR model ) taking into account such factors as ligand-ligand repulsion and polarization of the core electron shells of the central atom [158-160], In the latter case, many other factors must be considered, such as rf-electron configuration of the central atom, competition between a and n bonding, etc. (see discussion in [154]). 

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Valence bond theoiy also introduces the concept of directionality to chemical bonds. For example, we expect the bond formed by the overlap of a p orbital to coincide with the axis along which the p orbital lies. Consider the molecule H2S. Unlike the other molecules that we have encountered, H2S does not have the bond angle that Lewis theoiy and the VSEPR model would lead us to predict. (With four electron domains on the central atom, we would expect the bond angle to be on the order of 109.5 .) In fact, the H—S—H bond angle is 92°. Looking at this in terms... 

Throughout the book, theoretical concepts and experimental evidence are integrated An introductory chapter summarizes the principles on which the Periodic Table is established and describes the periodicity of various atomic properties which are relevant to chemical bonding. Symmetry and group theory are introduced to serve as the basis of all molecular orbital treatments of molecules. This basis is then applied to a variety of covalent molecules with discussions of bond lengths and angles and hence molecular shapes. Extensive comparisons of valence bond theory and VSEPR theory with molecular orbital theory are included Metallic bonding is related to electrical conduction and semi-conduction. 

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