Bonding in Molecular Crystals and their Characteristic
Depending on the forces that hold the atoms, molecules or ions together in crystal lattice crystals are classified into four main types.
Fig: bonding pattern in N8 molecules
Molecular crystal: The lattice points in molecular crystals are occupied by molecules which are held together either by relatively weak van der Waal’s force or hydrogen bonding. As a result the molecular crystals are soft and have low melting points. Solid sulfur dioxide (SO2) is an example of molecular crystal. The predominant force in solid sulfur dioxide is dipole-dipole interaction. Molecular solids are soft, often volatile, have low melting temperatures, and are electrical insulators. Ice is another example of molecular crystal which has a three dimensional lattice structure. Intermolecular hydrogen bonding is responsible for maintaining this three dimensional network in ice. Other examples of molecular crystals are I2, P4, S8, CCl4 etc.