Atomic interactions classification

Table I. Classification of atomic interactions on the basis of local topological and energetic properties at the bond critical point...

Interactions taking place between atoms are classifed into two categores viz., bonded class, and unbonded class. 

The sign and magnitude of the Laplacian of the charge density at the bond critical point, the quantity V Pb provide a classification of the mechanics of the atomic interactions involved in chemical bond formation. This aspect of the classification of the bonds in hydrocarbon molecules is now presented following an introduction to the properties of the Laplacian of a molecular charge distribution. 

Many observations concerning these trends had been made over the years, and in the 1950s S. Ahrland, J. J. Chatt, and M. Davies presented a classification of metals based on their preferred interaction with donor atoms. Class A metals are those that interact preferentially when the donor atom is in the first row of the periodic table. For example, they prefer to bond to N rather than P donor atoms. Class B metals are those which interact better when the donor atom is in the second row of the periodic table. For example, a class B metal would bond better to P than to N. The following table summarizes the behavior of metal atoms according to this classification. 

Following our general classification of hydrogen bonds, a negatively polarized hydrogen atom in H-Y, where Y is a less electronegative element than H (e.g., B, Al, Re, K, Mg, etc.), could be considered an unusual or nonconventional proton acceptor. Then the interaction... 

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