1. Oxidation and Reduction

2. Oxidation-Reduction
Oxidation-Reduction reactions are electron transfer reactions.
Also called Redox Reactions.

3. Oxidation: the loss of electrons
increases
Mg0  Mg2+
+ 2e-
(half rxn)
2-8-2
2-8
Mg lost 2 electrons = oxidized

4. Reduction: the gaining of electrons
reduces
S0 + 2e-  S2-
(half rxn)
2-8-6
2-8-8
S gains 2 electrons = Reduction

5. Redox When oxidation and reduction both take place.
**Electrons go from the metal to the nonmetal.
Mg + S  MgS (net equation)
Mg  lost electrons  oxidation
S  gains electrons  reduction

6. You can’t have one… without the other!
Reduction (gaining electrons) can’t happen without an oxidation to provide the electrons.
You can’t have 2 oxidations or 2 reductions in the same equation. Reduction has to occur at the cost of oxidation
LEO the lion says GER!
ose
lectrons
xidation
ain
lectrons
eduction
GER!

7. Another way to remember
OIL RIG s s
xidation
ose
eduction
ain

8. Review of Oxidation Numbers
The charge the atom would have in a molecule (or an
ionic compound) if electrons were completely transferred.
Free elements (uncombined state)  oxidation number = zero.
Na, Fe, K, Pb, H2, O2, P4 = 0
In compounds use periodic table and they add to zero.
2+ 2-
3+ 2-
Fe O
Fe2 O3
Polyatomic ions add to the charge on the ion.
+5 -2
= -1
N O3
N O3 -

9. Oxidation numbers of all the atoms in…?
+4 -2
+4 -2
S O2
C O3 2- -2
-3 +1
+1 -2
Na2 SO4
( )
(NH4)2S

10. Oxidation The oxidation number increases Metals oxidize
LEO (less electrons = oxidation)
Reduction needs to take place for there to be oxidation

11. Reduction The oxidation number decreases Nonmetals reduce
GER (gain electrons = reduction)
Oxidation needs to take place for reduction

12. Old definition:
Gaining oxygen = oxidation
Losing oxygen = reduction