Van der waals interactions result when hybrid orbitals overlap. a hydrogen atom loses an electron. molecules held by ionic bonds react with water. two polar covalent bonds react. electrons are not symmetrically distributed in a molecule.

Van der waals interactions are the electrical interactions between two or more atoms and even molecules but the inter-molecular attractions between the molecules are not exactly strong, in fact they are the weakest. And these Van der waals interactions are happened when electrons are not symmetrical distributed in a molecule.