THEORETICAL STUDIES ON SOLVATION: PART II. NEW THEORY FOR EVALUATION OF IONIC SOLVATION NUMBER FOR DIVALENT IONS AT 25 °C

Abstract

The concepts of ionic solvation are discussed and the definition of four types are suggested. Utilizing Webb's theory, values of the dielectric constant of water in terms of distance from a divalent ion are evaluated. The statistical mechanics of the distribution of solvent molecules round a divalent ion in aqueous solution has been worked out.The present theory shows that all divalent ions with radius less than 1.6 Å can have a saturated envelope of eight water molecules in excess of the Goldschmidt co-ordination number have to be accounted for as inner primary solvation number. The concept of catonium is suggested for such a stable aquo-complex entity. The catonium entity is further hydrated electrostatically in the normal way by primary and secondary solvation types. The conditions governing all types of solvation and their possible termination boundaries are discussed and evaluated.The theoretically calculated values of the ionic solvation numbers are in good agreement with the experimental results.