The answer is van der Waal force, or to be precise, London dispersion forces.
This type of force is present between all molecules and they are caused by electrons that are orbiting the atom cores. The moving of the electrons can result in making the atom temporary dipole due to the asymmetry of electron distribution around the core. This temporary dipole now can interact with other atoms leading to an electrostatic interaction. The more electrons an atom has, the stronger are these intermolecular forces.
