We'll learn how to determine the oxidation numbers or oxidation states for a the elements in a chemical compound. The oxidation numbers tell us how electrons are divided up or shared between atoms in a chemical compound. The oxidation numbers also tell us how electrons move in an oxidation reduction (redox) reaction. There are a set a rules that we use to determine oxidation number. Group 1A elements (alkalai metals) always have an oxidation of +1. Group 2A elements (alkaline earth metals) always have an oxidation number of +2. Elements on their own have an oxidation number of 0, and monatomic ions have an oxidation number that is equal to the ionic charge.