Ways of chemisorption modeling

The modeling of chemisorption is traditionally approached in two different ways. 

The first method, described as the chemical method, consists of identifying the active sites on the surface of the solid and expressing a bond between the adsoibate and the active site. This bond is a coordinate bond, obtained by pooling of doublets of electrons (Lewis acids and bases) either from the gas molecule or from a surface species of the solid this bond is more or less ionic. This is a concept of loealized adsorption. 

The second method, known as the electronic method, is based on the theoiy of energy bands of the solid and uses free electrons or electron holes of the solid. An electron or a hole is exchanged between the adsoibate and the adsorbent as a whole (at least the whole of the surface). This is then a delocalized approach with an electron. The model no longer takes into account the identification of the site of adsorption. 

These two approaches are eomplementaiy. According to the authors and the properly to be modeled, one of the two methods is employed. 

The field of reactivity of the solids, that is, the modeling of the mechanism of stoichiometric reactions of sohds, has also been confronted with such a dichotouty between a chemical description and an electronic description of the reactant or produced solids. Quasi-chemical modeling with structure elements makes it possible to cany out a synthesis of the two approaches and especially to anticipate certain properties, which is the essential condition so that modeling ean lead to applications. 

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