Water of crystallization

The water present in salts as water of crystallization is bound by the electrostatic attraction of the oxygen atoms of the water molecules for the metallic cation.

The metals in such salts have no partly occupied d-orbitals in their valence shells.

The structure of these hydrates can be quite elaborate, because of the existence of hydrogen bonds. Salts that contain water of crystallisation are called hydrated salts while salts that do not contain water of crystallisation are called anhydrous salts,

some examples of hydrated salts are: copper (II) sulphate, sodium carbonate, Nickel (II) sulphate, and Magnesium Sulphate

Note: UK English spelling – crystallisation.