The attractives forces that exists between molecules are known as intermolecular forces.
Intermolecular forces includes:
- Ionic Interactions
- Dipole-Dipole interactions
- Dispersion of London
The London dispersion force is the weakest intermolecular force and are referred to as Van der Waals Force.
Unequal position of electrons in molecule causes a rapid polarization and confer-polarization of the electron cloud forming short lived dipole. These dipole interact with the electron clouds of neighboring atom or molecule forming more dipoles.
They don’t exist on a long distance : about 1/r^6.
More the electrons cloud is high more it’s the polarizability of the molecule is easy and stronger is the London dispersion.
The dispersive interactions are always attractive.
This video explains very well London Dispersion:
and, an amazing natural application of the non-covalent interactions London dispersion is the Gecko. This animal is notorious for its climbing, prowess, regardless of the surface.