C. Lone elements and atoms in gases : 0
Elements in the free elemental have an oxidation number of zero
E. Elements in groups 1, 2, and 17 and polyatomic ions : Ionic charge
Group 1, 2, and 17 ions are formed by the alkali metals, alkaline metals and halogens respectively. Alkali metals, alkaline metals and halogens form +1, +2 and -1 ions respectively. Polyatiomic ions have -1, -2, -3 charges such as OH-, CO32-, PO43- respectively.
B. Hydrogen : +1, – 1 if bonded to a diatomic metal
H has an oxidation number of +1. H in metal hydrides such as NaH (sodium hydride) has an oxidation number of -1
A. Oxygen : Almost always –2
O has an oxidation number of -2.
D. Elements with multiple oxidation states : Determined by other elements in the compound
V (vanadium) has different oxidation which depends on the compound in which V is found.
