Why are ionic compounds usually hard?

Ionic compounds are usually hard due to the strong electrostatic forces of attraction between oppositely charged ions. These forces, known as ionic bonds, hold the ions together in a rigid crystalline structure.

Reasons for Hardness of Ionic Compounds:

1. Strong Electrostatic Forces
   • In ionic compounds, cations (positively charged ions) and anions (negatively charged ions) are held together by strong electrostatic forces.
   • These forces are very strong and require a large amount of energy to break.
2. Crystalline Structure
   • Ionic compounds form a well-organized, repeating pattern called a crystal lattice.
   • This arrangement makes the compound rigid and hard.
3. Less Flexibility
   • Unlike metals, ionic compounds do not have free electrons that allow flexibility.
   • The fixed positions of ions prevent them from bending or changing shape easily.
4. High Melting and Boiling Points
   • The strong bonding forces also result in high melting and boiling points.
   • This further indicates the hardness of these compounds.

Examples of Hard Ionic Compounds:

• Sodium chloride (NaCl)
• Magnesium oxide (MgO)
• Calcium carbonate (CaCO₃)

Thus, ionic compounds are hard due to their strong ionic bonds and rigid lattice structure.