Molecular solids are solids in which the building units are neutral molecules held together by intermolecular forces (not by ionic or metallic bonds).
Properties of Molecular Solids:
- Bonding
- Molecules are held by weak intermolecular forces (London dispersion, dipole–dipole, or hydrogen bonding).
- Hardness
- Usually soft because the intermolecular forces are weak.
- Melting and Boiling Points
- Have low melting and boiling points, since little energy is needed to overcome the weak forces.
- Electrical Conductivity
- Do not conduct electricity in solid or liquid state (no free ions or electrons).
- Solubility
- Non-polar molecular solids dissolve in non-polar solvents (like benzene).
- Polar molecular solids dissolve in polar solvents (like water).
- Examples
- Non-polar molecular solids: Iodine (I₂), Dry ice (solid CO₂).
- Polar molecular solids: Solid NH₃, Solid HCl.
- Hydrogen-bonded molecular solids: Ice (solid H₂O).
In short: Molecular solids are soft, have low melting points, are poor conductors, and are held together by weak intermolecular forces.