Interionic short range electrostatic interactions

From the thermodynamic viewpoint, the basic statistical theory is still too complex to provide useful working equations, but it does suggest forms of equations with some purely theoretical terms, and other terms including parameters to be evaluated empirically. In general, the theoretical terms arise from the electrostatic interactions which are simple and well-known while the empirical, terms relate to short-range interionic forces whose characteristics are qualitatively but not quantitatively known from independent sources. But, as we shall see, this division is not complete - there are interactions between the two categories. 

The molecule-molecule interactions, such as electrostatic forces between permanent dipoles or the dispersion interaction between molecules, and the ion-molecule interactions, such as ion-dipole electrostatic forces, are only significant at close range and their effects drop rapidly as the separation distance increases. The interionic electrostatic forces retain importance over a much greater distance. These long range forces therefore have the dominant effect in dilute solutions, but as concentrations Increase, so does the importance of the short range effects. 

The first is that hydration, or solvent structure-based interactions, is also to some extent of an electrostatic nature. For example, they involve interactions of ions with water dipoles and quadrupoles. Complex formation and chemical bond formation also involve electrical contributions. The difference with interionic coulomb forces between free ions is that this second category is typically short range. However, for the sake of argument, we shall heed the usual, but sloppy, distinction between electrical and chemical forces where the first category stands for the long-range coulombic interactions between free ions and the latter is... 

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