Molecular solids

In molecular solids the constituent particles are molecules. They are further divided into three categories:

1. Non-Polar Molecular Solids

These solids are formed from molecules or atoms that share a non-polar covalent bond. The atoms or molecules are held by weak dispersion force or by London forces.

• The physical nature of non-polar solids are soft.
• They don’t conduct electricity so they are insulators.
• They have a very low melting point.
• Examples: H₂, Cl₂, I₂ etc.

2. Polar Molecular Solids

• These solids are held together by polar covalent bonds and the atoms/molecules are bonded by relatively stronger dipole-dipole interactions.
• The physical nature is soft and most of these are gases or liquids at room temperature.
• They do not conduct electricity and they have a higher melting point than the non -polar molecular solids.
• Examples: HCl, SO₂, NH₃ etc.

3. Hydrogen-Bonded Molecular Solids

The solids contain polar covalent bonds with Hydrogen, Fluorine, Oxygen and Nitrogen atoms. In these solids, molecules are held together via strong hydrogen bonding.

• The physical nature of such solids are hard.
• They do not conduct electricity.
• The physical state of these solids are volatile liquids or soft solids under room temperature.
• They have a low melting point.
• Examples: H₂O (Ice ).