Hydrated ions of group 1 elemants

   Some Li‏⁺ salts containing small anions (e.g. LiF, Li₂CO₃) are sparingly soluble in water, but for large anions, the Li‏ salts are soluble while many K‏⁺, Rb‏⁺ and Cs⁺‏ salts are sparingly soluble (e.g. MClO₄, M₂[PtCl₆] for M = K, Rb or Cs)  Rb₂CO₃ is soluble in water, whereas RbClO₄ is sparingly soluble. Therefore, a suitable method of preparation is the neutralization of Rb₂CO₃ in aqueous HClO₄ with the formation of RbClO₄ precipitate. Caution! Perchlorates are potentially explosive.In dilute solutions, alkali metal ions rarely form complexes, but where these are formed, e.g. with [P₂O₇]^4_ and [EDTA]^4-  the normal order of stability constants is Li‏⁺> Na‏⁺> K⁺> Rb⁺> Cs‏. In contrast, when the aqueous ions are adsorbed on an ion-exchange resin, the order of the strength of adsorption is usually Li⁺‏ < Na⁺< K‏⁺< Rb‏⁺< Cs⁺ suggesting that the hydrated ions are adsorbed, since hydration energies decrease along this series and the total interaction (i.e. primary hydration plus secondary interaction with more water molecules) is greatest for Li..