Now notice, as shown in this diagram, this fe atom is bound to four nitrogen atoms. We have 1234. Now, fe can have an oxidation state of positive six. And in this particular case, because we have four bonds, what that means is this fe is in its ferrous state. And what that means is it has a state, an oxidation number of positive two. And so our fe atom at the center of the heme group can form two other bonds.