Redox reactions occur when one element is oxidized and another reduced in the same reaction. The sum of the oxidation numbers in a neutral compound is zero. The elements in Group VIIA often form compounds (such as AlF 3, HCl, and ZnBr 2) in which the nonmetal has a -1 oxidation number.Д©. Exceptions include molecules and polyatomic ions that contain O-O bonds, such as O 2, O 3, H 2O 2, and the O 2 2-В ion.ДЁ. Oxygen usually has an oxidation number of -2. The elements in Group IIA form compounds (such as Mg 3N 2В and CaCO 3) in which the metal atom has a +2 oxidation number.Д§. The metals in Group IA form compounds (such as Li 3N and Na 2S) in which the metal atom has an oxidation number of +1.Д¦. The oxidation number of hydrogen is -1 when it is combined with metal as in LiH, NaH, CaH 2, and LiAlH 4.ДҐ. The oxidation number of hydrogen is +1 when it is combined with a nonmetal as in CH 4, NH 3, H 2O, and HCl.Д¤. The oxidation number of sodium in the Na +В ion is +1, for example, and the oxidation number of chlorine in the Cl вЂ“В ion is -1.ДЈ. The oxidation number of simple ions is equal to the charge on the ion. Thus, the atoms in O 2, O 3, P 4, S 8, and aluminium metal all have an oxidation number of 0.Дў. The oxidation number of an atom is zero in a neutral substance that contains atoms of only one element. The oxidation number can typically be found above groups in the periodic table.ДЎ.

There is a fixed set of rules that can be followed to determine the oxidation number. The oxidation numberВ describes explicitly the degree to which an element can be oxidizedВ (lose electrons) or reduced(gain electrons).

TheВ oxidation numberВ is the effective charge on an atom in a compound the oxidation number is useful in determining theВ nomenclature, or name, of chemical compounds.

Oxidation numbers help