3. Oxidation Reduction Reactions
Redox Reactions
Electron-Transfer Reactions

4. Oxidation Numbers: A set of rules for tracking charges for
atoms in covalent compounds
Each atom in a pure element has an oxidation number of zero.
2. For monatomic ions, the oxidation number is equal to the charge on the ion.
3. Fluorine always has an oxidation number of –1 in compounds with all other
elements.
4. Cl, Br, and I always have oxidation numbers of –1 in compounds, except when
combined with oxygen or fluorine.
5. The oxidation number of H is +1 and of O is –2 in most compounds.
Exception for H: In compounds with metals, H is –1.
Exception for O: In peroxides, O22- ion gives O an oxidation number of –1.
6. The algebraic sum of the oxidation numbers for the atoms in a neutral compound
must be zero; in a polyatomic ion, the sum must be equal to the ion charge.

6. Oxidation States,
Energy,
the Economy, and
Global Warming

7. Oxidation-Reduction Reactions
Oxidation = loss of electrons = increase in ox #
Reduction = gain of electrons = decrease in ox #
4 Fe + 3 O2  2 Fe2O3
Oxidizing agent = oxidant = gains electrons
Reducing agent = reductant = loses electrons

8. Recognizing Redox Reactions: Always involves changes in oxidation numbers
Metals reacting with Nonmetals: 2 Al + 3 Br2  Al2Br6
Almost anything with Oxygen: 2 Mg + O2  2 MgO S + O2  SO2
Organic Compounds: CH4 + 2 O2  CO2 + H2O
Others, more difficult to detect: 5 Fe2+ + MnO H+  5 Fe3+ + Mn H2O

9. 4 Al(s) + 3 O2(g)  2 Al2O3(s)
2. CuO(s) + H2(g)  Cu(s) + H2O()

10. CaCO3(s)  CaO(s) + CO2(g)
4. MnO4-(aq) + 5 Fe2+(aq) + 8 H+(aq)  Mn2+(aq) + 4 H2O() + 5 Fe3+(aq)

11. 2 H2O2(aq)  2 H2O() + O2(g)
6. CaCO3(s) + 2 H+(aq)  CO2(g) + H2O() + Ca2+(aq)

12. Balancing Redox Reactions

13. Combination and Decomposition Reactions
Thermal decomposition of metal carbonates:
MCO3(s)  MO(s) + CO2(g)
Combination of two elements to form a compound
Zn + S  ZnS

14. Organic Reactions C3H8(g) + 5 O2(g)  3 CO2(g) + 4 H2O(l)
A. Combustion Reactions
Reaction with oxygen gas to form CO2 and H2O.
C3H8(g) + 5 O2(g)  3 CO2(g) + 4 H2O(l)
B. Substitution Reactions
Exchange of one atom or molecular fragment.

15. C. Addition Reactions
Addition of two molecules together.
D. Elimination Reactions
Ejection of a small molecule from a larger one.

16. E. Isomerization (Rearrangement) Reactions
Change of shape of a molecule without gain or loss of any atoms.