Physical Basis for Solvation Effects

The energy of solvation can be further broken down into terms that are a function of the bulk solvent and terms that are specifically associated with the first solvation shell. The bulk solvent contribution is primarily the result of dielectric shielding of electrostatic charge interactions. In the simplest form, this can be included in electrostatic interactions by including a dielectric constant k, as in the following Coulombic interaction equation  

This modification of the charge interaction is responsible for shifts in the electron density as permitted by the polarizability of the molecule. 

There are several effects present in the region where the molecule meets the solvent shell. The first is referred to as a cavitation energy, which is the energy required to push aside the solvent molecules, thus making a cavity in 

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