Now, any mass has energy, and Einstein showed this with the equation E equals MC squared. The larger the mass, the larger the energy. Electrostatic energy is the energy due to the attraction and repulsion of the protons in the nuclei or the nucleus and the electrons in the electron cloud, okay? This creates an electrostatic potential energy. Intermolecular energy is the energy due to neighboring molecules. If we go back to our system that's composed of two diatomic oxygen molecules, we see that the protons found on this nucleus will attract the electrons of the neighboring atom.