What are Van der Waals Forces?

Van der Waals forces are weak intermolecular forces that are dependent on the distance between atoms or molecules. These forces arise from the interactions between uncharged atoms/molecules.

For example, Van der Waals forces can arise from the fluctuation in the polarizations of two particles that are close to each other.

In the group of forces that fall under the category of ‘weak chemical forces’, Van der Waals forces are the weakest. They are known to rapidly vanish when the distance between the interacting molecules increases. The strengths of Van der Waals forces typically range from 0.4 kJ.mol^-1 to 4 kJ.mol^-1.

When the electron density around the nucleus of an atom undergoes a transient shift, it is common for Van der Waals forces arising. For example, when the electron density increases in one side of the nucleus, the resulting transient charge may attract or repel a neighbouring atom. The nature of these forces is dependent on the distance between the atoms:

• When the distance between the atoms is greater than 0.6 nanometres, the forces are extremely weak and cannot be observed.
• When the distance between the atoms ranges from 0.6 to 0.4 nanometres, the forces are attractive.
• If the interatomic distance is smaller than 0.4 nanometres, the forces are repulsive in nature.

An illustration detailing the induced formation of a dipole in an atom/molecule due to a fluctuating dipole in another atom/molecule is provided above. The adsorption of gaseous molecules to the surface of an adsorbent and the cohesion of condensed phases can be accounted for by Van der Waals forces.

Characteristics of Van der Waals Forces

• Covalent bonds and ionic bonds are significantly stronger than Van der Waals forces
• These forces are additive in nature, they are made up of several individual interactions
• These forces cannot be saturated
• No directional characteristic can be attributed to these forces
• They are not dependent on temperature (except dipole-dipole interactions)
• Van der Waals forces are short-range forces. Their magnitude is high when the atoms/molecules in question are close to each other.