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 ε_i= 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.