What is the primary cause of dispersion forces?

Dispersion forces, also known as London dispersion forces, arise primarily from the temporary uneven distribution of electrons within atoms and molecules. This phenomenon occurs because electrons are in constant motion, and at any given moment, they may be unevenly distributed around the nucleus of an atom or within a molecule. This transient distribution creates a temporary dipole, which can induce a dipole in a neighboring atom or molecule, resulting in a weak attraction between them.

The strength of dispersion forces increases with the size of the electron cloud—larger atoms or molecules have more electrons and tend to have greater fluctuations in electron density, leading to stronger dispersion forces. While other types of intermolecular forces such as dipole-dipole interactions and ionic bonds play significant roles in molecular interactions, they do not describe the origin of dispersion forces.