Oxidation Number

[Ashley 3A]

How do you easily identify the oxidation number of an element?

[Kaya Lu 2K]

The oxidation number of an element in groups 15-18 is typically the number of electrons an element would need to complete their valence shell. For example, the oxidation number of oxygen is always -2, and the oxidation number of fluorine is usually -1 within a polyatomic molecule. However, for elements in groups 1/2/13, their oxidation number is typically the number of valence electrons they have in their valence shell (magnesium is usually +2, lithium is usually +1, etc.). In general, you can determine oxidation numbers by process of elimination within a molecule by first assigning oxidation numbers to the elements that always take on a certain oxidation number and then determining what the oxidation numbers of the remaining elements would have to be in order for the oxidation numbers to add up to the overall charge of the molecule/ion. I would look up "oxidation number rules" for more information. I hope this helps!