129. What are important characteristics of ionic compounds?

(i) Stable existence: Ionic compounds usually exist in the form of crystalline solids. The crystals are made up of crystal lattices containing oppositely charged ions (+ve and –ve). Each cation is surrounded by a definite number of anions and vice-versa.

(ii)  High melting and boiling points and low volatility: There is a strong force of attraction among the oppositely charged ions in the crystals of ionic compounds, so a large amount of enthalpy is needed to separate them. Due to these strong forces of attraction, ionic compounds have high melting and boiling points and low volatility.

(iii) Electrical conductivity: Ionic compounds do not conduct electricity in the solid state because oppositely charged ions occupy fixed positions in the crystals and are not free to move. When these crystals are dissolved in a polar solvent or melted, the ions can move freely under the influence of electric field and become conductor of electricity.

(iv) Fast reactions: The chemical reactions between ionic compounds involve the combination between the ions liberated in their aqueous solutions. So their reactions are very fast.

(v) Solubility: Ionic compounds are soluble in polar solvents (e.g. water) and insoluble in nonpolar (organic) solvents. Polar solvents have high values of a dielectric constant which reduces the electrostatic force of attraction between the oppositely charged ions. Hence, the ions get separated and ultimately solvated by the molecules of the polar solvent.