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Determination
of Oxidation Number
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The
sum of the oxidation numbers of the atoms in a neutral molecule is equal
to 0.
The
sum of the oxidation numbers of the atoms in an ion is equal to the
charge of the ion.
- Atoms of an elemental
substance have an oxidation number of 0.
- Atoms of monoatomic
ioins have an oxidation number equal to the charge on the ion.
- The oxidation number
of fluorine is -1.
- The oxidation number
of oxygen is -2.*
- The oxidation number
of hydrogen is +1, except when hydrogen is in combination with metals
in binary compounds. When this is true, the oxidation number of hydrogen
is -1.
- The oxidation number
of the higher atomic number halogens (chlorine, Cl, Bromine, Br, and
iodine, I) is usually -1. See note.
Note:
When rules are in conflict, the earlier rule prevails. Thus, when chlorine,
bromine, or iodine is bonded to oxygen, the halogen will have an oxidation
number higher than 0. Furthermore, in an interhalogen compound the halogen
with the higher atomic number should be given the higher oxidation number.
*There are two exceptions
to this rule. First, when oxygen atoms in a compound are joined by an
-O-O- bond the oxidation number of oxygen is -1. Second, in the compound
OF2, the oxidation number of oxygen is +2.
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