So for example, if we have an H and an H, both nuclei have one protons each. If we have an F and an F, both nuclei have nine protons each and so on. Basically, when we have two of the same atoms, we're going to have a non polar covalent bond as we have here and as we have here. Now, notice we have a double bond here. But it doesn't change the fact that this is a nonpolar covalent bond because we have an oxygen with some amount of protons and a second oxygen with the same amount of protons. Now, another way to look at it is via electronegativity.