 Let's try carbon dioxide. We know its formula is CO2. First of all we look up the electronegativity of the two atoms and we can see that oxygen is the atom with the greater electron density. So it will have the partial negative charge and there are the pictures from the Molecules 360 database. Our next step is to draw the bond dipoles. So we draw the Lewis structure. We put in the bond dipoles which will go from the carbon out towards the oxygen. There they are. And then we sum the bond dipoles to draw the molecular dipole. Now if we have two dipoles that are of equal magnitude but in exactly opposite directions, what is their sum going to be? It's going to be zero, isn't it? We can show this if I just translate these down here. If I now draw the second dipole with its tail touching the head of the first, it will essentially go straight back in the other direction. So the sum is going to be zero. So when you look at the molecular dipole of carbon dioxide, it actually has none. And if a molecule has no molecular dipole, we say it is a non-polar molecule. Now this is an interesting case because this molecule has polar bonds, but because of its symmetry, because of the fact that the dipoles are in exactly opposite directions, it has no overall molecular dipole. So it is non-polar.