Ion‐Solvent Interaction and Individual Properties of Electrolytes

The experimental data concerning the individual behavior of monomonovalent electrolytes in respect to concentration dependence of osmotic coefficients, apparent molar refraction and apparent molar volume are discussed from the point of view of the structure of ions and of the solvent water. 2. New support is given to the conclusion that refractometric data show the existence in aqueous solutions of strong electrolytes of combinations of oppositely charged ions without water molecules between them. 3. The distinction between: (a) an undissociated molecule of a weak acid in which the proton penetrates deeply into the electronic shell of the anion; (b) a complex ion (e.g., CdCl 3 − in which the electronic shells are considerably deformed; (c) an associated ion‐pair of a strong electrolyte with a limited interpenetration and deformation of the electronic shells, is that of degree, not of principle. 4. Among the factors which are responsible for the individual behavior of strong electrolytes in aqueous solution, the following two are especially emphasized in this paper. The first factor is considered to be the resultant of the forces between neighboring ions and the forces between ions and the solvent; it is clearly responsible for the ease with which ions can be separated by the solvent molecules from a crystal lattice. The influence of this factor on the behavior of electrolytes is such as if oppositely charged ions would compete for the solvent molecules. The second factor depends on the interaction between free ions and the solvent. The first factor predominates at higher concentrations, the second at lower. 5. The tetrahedral structure of liquid water and the lack of spherical symmetry of NH 4 + , OH 3 + and ( H 2 O . Li ) + are responsible for the difference in the behavior of solutions of these ions as compared with those of other alkali ions. The application of the macroscopic dielectric constant of water to the solutions of both these groups of ions is not adequate, even in the region of the smallest concentrations investigated.