Below are particulate level models of a collection of atoms which only London Dispersion forces occur.
When looking at the movie ask the students what do they see? (See yellow spheres that could represent a noble gas atom or a nonpolar molecule. The important point is the spherical shape represents the volume occupied by the electrons in the noble gas atom or molecule. That the shape is spherical, symmetrical, suggests that the electrons are symmetrically distributed in the atom or molecule.)
So the yellow shape is representative of the electron distribution in the atom. NOTE: there is a moment in the movie where one of the yellow spheres turns many different colors, and then rotates around to reveal a look on the inside of the atom that has been sliced in half. This particular section of the movie was to reveal the symmetric distribution of electrons inside the shape. Unfortunately this brief section does not show up very well.
The next change in the movie shows one of the yellow spheres in a different shape. Ask students what might have happened to cause the shape of the electron density around the atom to change? (Since the shape is representative of the electron distribution, a different shape means that the electrons for that atom are no longer symmetrically distributed. Notice how the shape rotates to reveal the electron distribution. Also to help clarify, see the δ+ (partial positive charge) and δ- (partial negative charge) that is super-imposed over the atom with the asymmetric distribution of electrons.) Now watch how the single atom with the asymmetric distribution of electrons affects the atoms near it. Notice how the side of the atom with the partial positive charge induces a partial negative charge on the side of the atom adjacent to the original atom. This happens to many of the atoms near the first atom. Then in the next instant the asymmetric distribution of electrons changes. What this model has just demonstrated is what is referred to as an instantaneous dipole (a dipole that does not last very long). A nonpolar substance has no permanent dipole, however, a nonpolar atom or molecule can have an instantaneous dipole. Instantaneous dipoles arise when the normal symmetric distribution of electrons is distorted for an instant, resulting in an instantaneous dipole. For nonpolar molecules containing atoms from the first and second period the only intermolecular attractive force that can occur is London dispersion forces, and the London dispersion force is the weakest IMAF when compared to dipole dipole forces or hydrogen bond.