Why are lithium salts commonly hydrated and those of the other alkali ions usually anhydrous?
Lithium salts are commonly hydrated and those of the other alkali ions usually anhydrous.
Explanation:
The hydration enthalpies of alkali metal ions decrease with increase in ionic sizes.
Li+ > Na+ > K+ > Rb+ > Cs+
⇒ Because of smallest size among alkali metals, Li+ can polarise water molecules more easily than the other alkali metal ions.
⇒ As a result, water molecules get attached to lithium salts as water of crystallisation.
⇒ Hence, Li+ has maximum degree of hydration enthlpy and for this reason lithium salts are mostly hydrated.
⇒ For example, lithium chloride crystallises as LiCl 2H2O
Note: Hydration enthalpy is defined as the energy released when new bonds formation takes place between the ions and the water molecules.
