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The oxidation number of the sulfur atom in the SO 4 2- ion must be +6, for example, because the sum of the oxidation numbers of the atoms in this ion must equal -2.ġ1. The sum of the oxidation numbers in a polyatomic ion is equal to the charge on the ion. The sum of the oxidation numbers in a neutral compound is zero.ġ0. 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.ĩ. 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- ion.Ĩ. Oxygen usually has an oxidation number of -2. The elements in Group IIA form compounds (such as Mg 3N 2 and CaCO 3) in which the metal atom has a +2 oxidation number.ħ. 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.Ħ.
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The oxidation number of hydrogen is -1 when it is combined with a metal as in. The oxidation number of hydrogen is +1 when it is combined with a nonmetal as in CH 4, NH 3, H 2O, and HCl.Ĥ. The oxidation number of sodium in the Na + ion is +1, for example, and the oxidation number of chlorine in the Cl - ion is -1.ģ. 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 aluminum metal all have an oxidation number of 0.Ģ. The oxidation number of an atom is zero in a neutral substance that contains atoms of only one element.
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The rules are presented in order with the previous rule superseding the next.ġ. The determination of the oxidation number (or oxidation state) of chemical compounds can be made by following a few simple rules.
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