Calculations on Ionic Solvation Part 1.—Free Energies of Solvation of Gaseous Univalent Ions Using a One-layer Continuum Model

Abstract

The electrostatic free energy of solvation of an ion has been calculated using a model in which an ion of radius a and dielectric constant εi= 1 is surrounded by a solvent layer of thickness (b–a) and dielectric constant ε1, immersed in the bulk solvent of dielectric constant ε0. The electrostatic energy is combined with the nonelectrostatic free energy of solvation, obtained from experimental data on the free energy of solution of gaseous non-polar solutes, to yield the total free energy of solvation of a gaseous ion in a solvent. It is found that when a is taken as the ionic crystal radius, (b–a) as the solvent radius and ε1= 2 there is excellent agreement with experiment for the solvation of gaseous univalent cations and anions in the solvents, 1,1-dichloroethane, 1,2-dichloroethane, tetrahydrofuran, 1,2-dimethoxyethane, ammonia, acetone, acetonitrile, nitromethane, 1-propanol, ethanol, methanol and water. Limited data suggest that the method can also be applied to solution of ions in benzene, bromobenzene, chlorobenzene, ethyl benzoate, ethyl acetate and nitrobenzene.