CBSE Class 10 Science 2019 · Paper 31/3/1 · Question 3

Ionic compounds: Compounds formed by the transfer of electrons from a metal to a non-metal are called ionic (electrovalent) compounds. They are made of positive and negative ions held together by strong electrostatic forces of attraction, for example sodium chloride, ${\text{Na}}^{+}{\text{Cl}}^{-}$, and magnesium chloride, ${\text{MgCl}}_2$. Why the solid does not conduct: Electricity is conducted by the movement of charged particles. In the solid state the ions are held in fixed positions in a rigid crystal structure by strong electrostatic attraction, so they cannot move, and there are no free ions or free electrons. Hence solid ionic compounds do not conduct electricity. (When melted or dissolved in water, the ions become free to move and the compound conducts.)