2. Oxidation and Reduction (Redox)
Electrons are transferred
Spontaneous redox rxns can transfer
energy
Electrons (electricity)
Heat
Non-spontaneous redox rxns can be
made to happen with electricity
3. Oxidation Reduction Reactions
(Redox)
Each sodium atom loses one electron:
Each chlorine atom gains one electron:
1
1
2
0
0
2
2
Cl
Na
Cl
Na
e
Na
Na
1
0
1
0
Cl
e
Cl
4. LEO says GER :
Lose Electrons = Oxidation
Sodium is oxidized
Gain Electrons = Reduction
Chlorine is reduced
e
Na
Na
1
0
1
0
Cl
e
Cl
5. Rules for Assigning Oxidation Numbers
Rules 1 & 2
1. The oxidation number of any uncombined
element is zero
2. The oxidation number of a monatomic ion
equals its charge
1
1
2
0
0
2
2
Cl
Na
Cl
Na
6. Rules for Assigning Oxidation Numbers
Rules 3 & 4
3. The oxidation number of oxygen in
compounds is -2
4. The oxidation number of hydrogen in
compounds is +1
2
2
1
O
H
7. Rules for Assigning Oxidation Number
Rule 5
5. The sum of the oxidation numbers
in the formula of a compound is 0
2(+1) + (-2) = 0
H O
(+2) + 2(-2) + 2(+1) = 0
Ca O H
2
2
1
O
H 2
1
2
2
)
(
H
O
Ca
8. Rules for Assigning Oxidation Numbers
Rule 6
6. The sum of the oxidation numbers in the
formula of a polyatomic ion is equal to
its charge
X + 3(-2) = -1
N O
X = +5 X = +6
X + 4(-2) = -2
S O
3
2
?
O
N
2
4
2
?
O
S
9. The Oxidation Number Rules -
SIMPLIFIED
1. The sum of the oxidation numbers in
ANYTHING is equal to its charge
2. Hydrogen in compounds is +1
3. Oxygen in compounds is -2
10. Not All Reactions are Redox Reactions
Reactions in which there has been no change
in oxidation number are not redox rxns.
Examples:
1 5 2 1 1 1 1 1 5 2
3 3
( ) ( ) ( ) ( )
Ag N O aq NaCl aq Ag Cl s Na N O aq
1 2 1 1 6 2 1 6 2 1 2
2 2
4 2 4
2 ( ) ( ) ( ) ( )
NaO H aq H S O aq Na S O aq H O l
11. Reducing Agents and Oxidizing Agents
The substance reduced is the oxidizing agent
The substance oxidized is the reducing agent
Sodium is oxidized – it is the reducing agent
Chlorine is reduced – it is the oxidizing agent
e
Na
Na
1
0
1
0
Cl
e
Cl
This slide refers to vocabulary that has been excluded from AP
Chemistry by the College Board, and will not be tested.
12. Trends in Oxidation and Reduction
Active metals:
Lose electrons easily
Are easily oxidized
Active nonmetals:
Gain electrons easily
Are easily reduced
