* Contain water molecules coordinated to the metal ion.

* The water molecules are held in place by hydrogen bonding to the metal ion and to each other.

* The number of water molecules coordinated to the metal ion is called the hydration number.

* Hydrated salts are typically more soluble in water than anhydrous salts.

* Examples of hydrated salts include copper(II) sulfate pentahydrate (CuSO₄·5H₂O) and sodium chloride dihydrate (NaCl·2H₂O).

Anhydrous salts:

* Do not contain any water molecules coordinated to the metal ion.

* Anhydrous salts are typically less soluble in water than hydrated salts.

* Examples of anhydrous salts include copper(II) sulfate (CuSO₄) and sodium chloride (NaCl).

The difference between hydrated salts and anhydrous salts is due to the presence or absence of water molecules coordinated to the metal ion. This can have a significant impact on the physical and chemical properties of the salt, such as its solubility, color, and melting point.