What Makes Molecules Have High Attractive Forces

Intermolecular forces, named after van der Waals, that occur between atoms or molecules. These forces of attraction arise from the fact that atoms can form extremely short-lived dipoles. One side of the atom then has a slightly stronger negative charge than the other (asymmetrical charge distribution).

If atoms approach each other and the charge is shifted synchronously in both atoms, attractive forces act from a certain distance, which are referred to as van der Waals forces. The positively polarized part of one atom attracts the negatively polarized part of the other atom.

Approximation of atoms with asymmetrical charge distribution
Effect of
Van der Waals forces

If only one atom has a charge shift (dipole) at the time of approach, it can induce a charge shift in the other atom, so that in turn the positively polarized part of one atom attracts the negatively polarized part of the other atom.

Approach of a molecule with an asymmetrical charge distribution (A) to a molecule with a symmetrical charge distribution (B)Induction of a dipole in molecule B and the effect of van der Waals forces

The possibility of polarization increases with increasing surface area of ​​the atom and is greater the further the outer electrons are away from the nucleus. For this reason, the van der Waals forces increase with increasing atomic or molecular mass.