Factors affecting the solubility of ionic compounds

In order to provide a more robust understanding for the general solubility rules provided in most chemistry introductions, the charge densities for common ionic cations and anions are computed via quantum chemical methods. It is shown that low charge densities on either the cation or, especially, the anion promote solubility. The lowest anion charge densities produced correspond to chlorate, perchlorate, and acetate which are known always to be soluble for the analyzed cations. Silver has the lowest charge density of the cations examined, but is rarely soluble, only with these three singly-charged polyatomic anions and the related nitrate anion. The silver chloride bond is 8. kcal/mol stronger than silver chlorate and 12. kcal/mol stronger than silver nitrate. Sodium chloride is 6. kcal/mol weaker than silver chlorate with potassium chlorate 8. kcal/mol weaker. Hence, silver monomer salts are shown here to produce high bond energies to atomic anions showcasing why charge density alone cannot explain aqueous solubility, even though it is a good marker in a general sense.