Molecular geometry 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. 

In Chapter 7, we used valence bond theory to explain bonding in molecules. It accounts, at least qualitatively, for the stability of the covalent bond in terms of the overlap of atomic orbitals. By invoking hybridization, valence bond theory can account for the molecular geometries predicted by electron-pair repulsion. Where Lewis structures are inadequate, as in S02, the concept of resonance allows us to explain the observed properties. 

VSEPR model Valence Shell Electron Pair Repulsion model, used to predict molecular geometry states that electron pairs around a central atom tend to be as far apart as possible, 180-182... 

Tetrahedral molecular geometry, with 109.5° bond angles, minimizes repulsion among the bonding electron pairs of methane. ... 

The molecular geometry of a complex depends on the coordination number, which is the number of ligand atoms bonded to the metal. The most common coordination number is 6, and almost all metal complexes with coordination number 6 adopt octahedral geometry. This preferred geometry can be traced to the valence shell electron pair repulsion (VSEPR) model Introduced In Chapter 9. The ligands space themselves around the metal as far apart as possible, to minimize electron-electron repulsion. 

The other approach to molecular geometry is the valence shell electron-pair repulsion (VSEPR) theory. This theory holds that... 

Molecular Geometry The Valence Shell Electron-Pair Repulsion (VSEPR) Model... 

Due to the simplicity and the ability to explain the spectroscopic and excited state properties, the MO theory in addition to easy adaptability for modern computers has gained tremendous popularity among chemists. The concept of directed valence, based on the principle of maximum overlap and valence shell electron pair repulsion theory (VSEPR), has successfully explained the molecular geometries and bonding in polyatomic molecules. 

We are now prepared to examine how attractive or repulsive nonbonded interactions determine molecular geometry. We shall discuss representative examples where pi and/or sigma nonbonded interactions obtain. In each case, we provide computational data in support of general theoretical arguments as well as pertinent experimental results. It should be mentioned that only crucial indices of nonbonded interactions are provided and the survey of the experimental work is by necessity incomplete, i.e., it would take volumes to consider all available data. Nonetheless, at the end of this chapter, the reader should be able to apply the key ideas to problems of direct interest to him. 

Molecular geometry, the arrangement of atoms in three-dimensional space, can be predicted using the VSEPR theory. This theory says the electron pairs around a central atom will try to get as far as possible from each other to minimize the repulsive forces. 

It appears that the electron pair repulsions ana atom-atom interactions both are important in establishing the molecular geometry. The actual structure depends on the relative magnitude of the various interactions. 

Valence-shell electron-pair repulsion A model that explains molecular geometries in terms of electron pairs striving to be as far apart from one another as possible. 

Thus far, attention has been focused on the guest molecules in their ground states. This is so because it is relatively easy to predict and visualize the geometry and orientation of molecules within reaction cavities based on attractive and repulsive interactions between ground state guest molecules and the host structure. However, electronic excitation frequently lead to changes in molecular geometry and polarizability [97], For example, it is well known that formaldehyde becomes pyramidal upon excitation and the C—O... 

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