Theory of electrolytes. Part 4.—Model of polarisable dielectric spheres. “Structure” around ions in solution in relation to ionic solvation and activity coefficients

Abstract

In a modification of the previous model, the representation of solvated ions as polarisable spheres of dielectric gives realistic activity coefficients. Predictions of the new treatment are examined for three types of non-spherical ionic cloud. Each specific structure of the ionic cloud leads to a characteristic family of curves which can be distinguished by the size and dielectric constant of the ion–solvent complex. A rôle for ionic solvation in promoting lattice-like structures in solutions is suggested.

Further analysis of electrostatic contributions to the non-ideal part of the chemical potential reveals an incomplete cancellation of ionic self-energies and interaction energies, which leads to the upturn of activity coefficients at higher concentrations.