APPLICATION OF THE MEAN SPHERICAL APPROXIMATION TO DESCRIBE THE GIBBS SOLVATION ENERGIES OF MONOVALENT MONOATOMIC IONS IN POLAR-SOLVENTS

The mean spherical approximation for the ion-dipole mixture is used to study the solvation energies of monovalent monoatomic ions in polar solvents. From the structure of the analytical solution it is inferred that there are two parameters that should be used to describe the solvation: the dielectric constant and a polarization parameter which plays the role of a mean-field parameter to account for nonsphericity, chemical interactions, and other effects related to failure of the hard-sphere model for the system. The model was successfully fitted to data for the Gibbs solvation energy of five alkali-metal cations and three halide ions in 17 different solvents including water. On the basis of this analysis, it was shown that a single value of the polarization parameter describes the data for the cations in each solvent, a quite different value being appropriate for the anions. The polarization parameters were found to be linearly correlated with empirical parameters characterizing the solvent's basicity (DN) in the case of cations and its acidity (E(T)) in the case of anions.