Atomic-interaction-based theory chemical bonding

Empirically measured parameters are additional solvent properties, which have been developed through the efforts of physical chemists and physical organic chemists in somewhat different, but to some extent related, directions. They have been based largely on the Lewis acid base concept, which was defined by G. N. Lewis. The concept originally involved the theory of chemical bonding which stated that a chemical bond must involve a shared electron pair. Thus, an atom in a molecule or ion which had an incomplete octet in the early theory, or a vacant orbital in quantum mechanical terms, would act as an electron pair acceptor (an acid) from an atom in a molecule or ion which had a complete octet or a lone pair of electrons (a base). Further developments have included the concepts of partial electron transfer and a continuum of bonding from the purely electrostatic bonds of ion-ion interactions to the purely covalent bonds of atoms and molecules. The development of the concept has been extensively described (see Ref. 11 for details). 

There are currently three different approaches to understanding chemical bonding. Quantum mechanical calculations see Ab Initio Calculations, Molecular Orbital Theory), even though they give the most complete picture, offer few insights into the nature of chemical bonds themselves because the concept of a bond does not arise naturally from a formahsm based on the interactions between nuclei and electrons rather than the interaction between atoms. Even though quantum mechanics gives accurate values for measurable properties, its calculations are compnter intensive and it becomes more difficult to use the more complex the chemical system. 

Among the most important requirements in the theory of chemical bonds is the development of a unified method for the description of the chemical interaction between atoms, which would be based on the structure of the atomic electron shells and in which one would utilize the wave functions and the electron density distributions calculated for isolated (free) ions on the basis of the data contained in Mendeleev s periodic table of elements. This unified approach should make it possible to elucidate the interrelationship between the various physical properties and the relationship between the equilibrium and the excited energy states in crystals. In contrast to the study of chemical bonds in a molecule, an analysis of the atomic interaction in crystals must make allowances for the presence of many coordination spheres, the long- and short-range symmetry, the long- and short-range order, and other special features of large crystalline ensembles. As mentioned already, the band theory is intimately related to the chemi-... 

From a conceptual point of view, the interaction of an atom or molecule with a solid surface involves the same forces that are known from the theory of chemical bonding. However, there is an important difference with respect to the gas-phase scenario, namely the dimensionality of one of the partners. The surface is a macroscopic medium with an infinite number of electrons that interact with an individual atom or molecule. In spite of this difference, some basic similarities remain, and many of the concepts present in the theory of chemical bonding can be transferred to the molecule-surface interaction. For example, the strength of the interaction is based on the types of force involved. In the case of molecule-metal interactions, two broad categories can he distinguished, namely (i) weak interaction, leading to physisorption, and (ii) strong interaction, which is responsible for chemisorption. 

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