Oxidation Numbers

Oxidation States

Useful in oxidation-reduction (redox) reactions.

 

Rule	Answer
An atom in an element has this oxidation state	0
A monatomic ion with charge +n has this oxidation state	+n
A monatomic ion with charge -n has this oxidation state	-n
Most O in covalent compounds have this oxidation state	-2
O in peroxides have this oxidation state	-1
H in covalent compounds with nonmetals have this oxidation state	+1
Flourine always has this charge and oxidation state*	-1
In binary compounds, the element that more strongly attracts electrons gets a negative charge -n and this oxidation state	-n
The sum of oxidation states for all atoms in a neutral compound	0
The sum of oxidation states for all atoms in a compound with charge +n	+n
The sum of oxidation states for all atoms in a compound with charge -n	-n
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* This rule above does not seem to apply in HOF where F has the oxidation state +1,
   as listed below.

 

Fill in the blank	Answer
Atoms with oxidation states that rise during a reaction are ___.	oxidized
Atoms with oxidation states that fall during a reaction are ___.	reduced
Atoms that gain electrons during a reaction are ____.	reduced
Atoms that lose electrons during a reaction are ____.	oxidized
An oxidizing agent contains an atom that is ____ during a reaction.	reduced
A reducing agent contains an atom that is ____ during a reaction.	oxidized
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Atom	Oxidation State
Na(s)	0
Al(s)	0
Hg(l)	0
O in O2	0
O in O3	0
I in I2	0
Cl in Cl2	0
Na+	+1
Fe3+	+3
Mn2+	+2
H-	-1
H in H2-	-1/2
H in LiH	-1
Li in LiH	+1
H in CaH2	-1
Ca in CaH2	+2
O in H2O2	-1
H in H2O2	+1
O in O22-	-1
O in O2-	-1/2
K in KO2	+1
O in KO2	-1/2
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Atom	Oxidation State
S in S2O32-	+2
O in S2O32-	-2
S in S4O62-	+5/2
O in S4O62-	-2
Fe in Fe3O4	+8/3 (actually two are +3 and one is +2)
O in Fe3O4	-2
C in CH4	-4
H in CH4	+1
C in CO2	+4
O in CO2	-2
H in H2O	+1
O in H2O	-2
Na in NaCl	+1
Cl in NaCl	-1
S in PbS	-2
Pb in PbS	+2
S in SO2	+4
O in SO2	-2
Cr in Cr2O72-	+6
O in Cr2O72-	-2
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Atom	Oxidation State
N in NH3	-3
N in N2H4	-2
N in NH2OH	-1
N in N2	0
N in N2O	+1
N in NO	+2
N in N2O3	+3
N in NO2	+4
N in HNO3	+5
S in SO3	+6
S in H2SO4	+6
S in SO42-	+6
S in SF6	+6
S in SO2	+4
S in HSO3-	+4
S in SO32-	+4
S in SF4	+4
S in SCl2	+2
S in S8	0
S in H2S	-2
S in S2-	-2
Halogen in HOF, HOCl, HOBr, HOI	+1
Halogen in HOClO	+3
Halogen in HOClO2, HOBrO2, HOIO2	+5
Halogen in HOClO3, HOBrO3, HOIO3	+7
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Reference

Chemistry by Steven S. Zumdahl, D.C. Heath and Company, 1986.

 

Oxidation Numbers 2 and Oxidation Numbers 3 give more.