Intermolecular Forces

Intermolecular forces are the forces of attraction that act between molecules. They are fundamentally different from the covalent bonds that hold atoms together within molecules. Intermolecular forces are much weaker than covalent bonds, but they have enormous influence on physical properties such as boiling points, melting points, and solubility.

There are three types of intermolecular force, in order of increasing strength: London dispersion forces, permanent dipole–dipole interactions, and hydrogen bonding.

---

London Dispersion Forces (Temporary Dipole–Induced Dipole)

London dispersion forces (also called van der Waals forces, dispersion forces, or temporary dipole–induced dipole forces) are the weakest intermolecular force, but they are present in all molecules and are the only intermolecular force in non-polar molecules.

How They Arise

At any given instant, the electrons in an atom or molecule may be unevenly distributed, creating a temporary (instantaneous) dipole — a brief, random imbalance of charge. This temporary dipole induces a dipole in a neighbouring molecule by attracting or repelling its electrons. The result is a fleeting attraction between the two molecules.

These temporary dipoles are constantly forming, disappearing, and re-forming. Although each individual interaction is extremely short-lived, the cumulative effect across billions of molecules produces a significant attractive force.