How can a molecule have a momentary

Electrons are constantly in movement. Temporarily dipoles can occur in non-polar molecules when electrons move around and spontaneously come into close proximity with each other and become concentrated on one atom. When this happens one atom becomes temporarily more negatively charged than the other atom. Thus creating a momentary dipole.

Here is my answer to your question  it is by a random momentary clustering of electrons in one particular point of an atom or molecule that is how a molecule have a momentary dipole. AND hope u enjoy my answer.