### Oxidation States

```Oxidation States
Oxidation State: the apparent charge that an
atom would have if electron pairs in covalent
bonds belonged entirely to the more
electronegative atom
Oxidation Number: positive or negative
number assigned to an atom based on its
oxidation state
“Electron bookeeping”
Common Oxidation Numbers
(p. 658)
Atom or Ion
Oxidation #
Examples
atoms in elements
0
Fe, C, O2, F2
hydrogen
+1
HCl, NH3
hydrogen with metals
-1
NaH, CuH2
oxygen
-2
H2O, FeO, NO3-
oxygen in peroxides
-1
H2O2
ion charge
Mg2+, Na+, S2-
monoatomic ions
Determining Oxidation Numbers
• Assign common oxidation numbers
• The sum of oxidation numbers for a compound is
0
• The sum of oxidation numbers for a polyatomic ion
is its charge
• Use algebra to determine any unknown oxidation
numbers
Examples:
K2SO4
K2Cr2O7
MnO4-
Redox Reactions
• Oxidation numbers change in a redox reaction
• Oxidation is an increase in oxidation number
• Reduction is a decrease in oxidation number
Ca(s) + Cl2(g)  CaCl2(s)
CH4(g) + 2O2(g)  CO2(g) + 2H2O(l)
Practice
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