Ionic compounds are usually formed when metals react with non-metals”. ... This electrostatic force is the main reason for hardness of ionic compounds. The oppositely charged ions in an ionic compound are packed tightly with each other and form a crystalline structure which is very hard and rigid.

Why ionic compounds are usually hard?

The ionic compounds are usually hard because the ions are held by strong electrostatic force of attraction as the positive and negative ions are strongly attracted to each other and difficult to separate them apart.

Why do ionic compounds are strong?

Ionic bond is much stronger than covalent bond because it involves complete transfer of electrons because of which there is formation of cation and anion and there exist huge electrostatic forces of attraction. They also have high melting and boiling point which proves that the ionic bond is very strong.