Now when an element gains a charge, it's no longer in its standard or natural state, so its oxidation will no longer be equal to 0. Now ions recall an ion is an element or compound with a positive or negative charge. Remember your positive ions are called cations and your negative ions are called your anions.
Now for a monoatomic ion, the oxidation number is equal to its charge. So if they gave us for example, the aluminum ion, aluminum is in Group 3A, so it charges 3+. If we see a charge present for that element, that is also its oxidation number. OK. But remember, it has to be in its ion form for the charge and oxidation number to equal one another.
OK, that's not always going to be the case. We're going to see later on there going to be cases where a particular element, its oxidation number, can range widely based on what it's connected to. But for right now, if you see an ion, you see its charge. That charge is equal to its oxidation number. So keep that in mind as we click on the next video and attempt an example question.