And so one of the electrons will be pulled away from the metal atom and onto the oxygen, giving this diatomic oxygen a negative charge. And this is called a superoxide ion. In fact, this superoxide ferric ion complex is the resonance structure that more closely describes what the structure is between these two atoms, the two oxygen atoms and the single metal atom. So we see that when the diatomic oxygen binds onto that fe from the top, that diatomic oxygen develops a negative charge because it is more electronegative and it pulls away those electrons, that electron, from the metal atom. And that's precisely what moves this entire residue up and what allows this metal atom to fit into the sensor portion of that protoporphy in group. Now, because the diatomic oxygen gains a negative charge, it becomes slightly less stable.