Intermolecular Forces

This section is concerned with the forces between molecules, as opposed to the forces between atoms in molecules.

Intermolecular forces are weak attractive forces between molecules. Without these forces there would be no molecular solids, gases or liquids.

These weak forces arise from electrostatic forces between dipoles (charges molecules). 

Some molecules have:

• permanent dipoles
• instantaneous dipoles.

Important point:

• Covalent bonds within a molecule are strong and difficult to break up.
• If a liquid boils, then molecules are separating, not breaking up

 In a covalent compound, forces between particles (intermolecular forces) are generally very weak.

 There are 3 main types of attractive force between molecules. They are all quite weak; chemists call them DIPOLES.

Relative magnitude of 

van der Waal’s : Hydrogen bonding: covalent

                                                1: 10:1000

Polar molecules

Dipole-Dipole Interactions (van der Waals)

Hydrogen Bonding