What causes instantaneous dipoles in non-polar molecules?

Instantaneous dipoles in non-polar molecules are caused by the random, momentary uneven distribution of electrons around the atoms.

In more detail, all atoms and molecules, whether polar or non-polar, are composed of charged particles: protons, neutrons, and electrons. The protons and neutrons reside in the nucleus of the atom, while the electrons orbit the nucleus in a cloud-like formation. Even in non-polar molecules, where the electrons are shared equally between atoms, these electrons are constantly moving. This movement is random and fast, leading to instances where there may be a temporary uneven distribution of electrons around the atoms.

At any given moment, there could be more electrons on one side of the atom or molecule than the other, creating a temporary or 'instantaneous' dipole. This dipole lasts only for an instant, until the electrons move again. However, because there are so many electrons and their movement is so fast, these instantaneous dipoles are constantly being created and destroyed.

These instantaneous dipoles can induce dipoles in nearby atoms or molecules, leading to attractive forces known as London dispersion forces or van der Waals forces. These are the weakest type of intermolecular force, but they can become significant in molecules with many electrons (such as large or long-chain molecules) where there are more opportunities for instantaneous dipoles to occur.

In summary, instantaneous dipoles in non-polar molecules are caused by the random, momentary uneven distribution of electrons around the atoms. This is a natural result of the constant, fast movement of electrons. These dipoles are temporary, but they occur frequently due to the large number of electrons and their rapid movement. They can induce dipoles in nearby atoms or molecules, leading to weak intermolecular forces known as London dispersion forces.