Oxidation Number

The oxidation number of an atom is the charge that atom would carry if the compound it is a part of were composed of ions.

Rules for Assigning Oxidation Numbers

Rule	Example
	Compound	Oxidation numbers of atoms
If compound is neutral and contains only one element, oxidation number of atoms must be zero	S8 H2	S: 0 H: 0
Oxidation number of simple ions is equal to the charge on the ion	Na+ I-	Na: +1 I: -1
When H is bound to a non-metal, its oxidation number is +1	CH4 H2O	H: +1, C: -4 H: +1, O: -2
When H is bound to a metal, its oxidation number is -1	NaH LiAlH4	H: -1, Na: +1 H: -1, Li: +1, Al: +3
Elements toward the bottom left corner of the periodic table are more likely to form positive oxidation states than elements toward the upper right corner	SO2 XeF4 NO3-	S: +4, O: -2 Xe: +4, F: -1 N: +5, O: -2