1. POWER POINT PRESENTATION ON OXIDATION NUMBERS

2. Redox Chemistry Redox means reduction-oxidation reactions.
Reduction - when an atom gains electrons (thereby “reducing” the oxidation number of that element).
Oxidation - when an atom loses electrons (thereby increasing the oxidation number of that element).

3. OIL RIG O - Oxidation I - Is L - Losing electrons R - Reduction I - Is
G - Gaining electrons

5. What are Oxidation Numbers?
Oxidation Numbers are the charges that an atom or ion has or “appears” to have.
Example: H2O
Each H has a +1
and the O has a -2
Total = 2 (+1) = zero charge on the molecule

7. RULES FOR OXIDATION 1. The oxidation # of a free element is zero.
Example: Na0, C0, He0, O20, Cl20
Note that some elements are naturally diatomic.

8. RULES FOR OXIDATION 2. The oxidation # of a simple ion is its charge.
Cl-1 is O-2 is Na+1 is +1

9. RULES FOR OXIDATION
3. Group 1 metals found in compounds have an oxidation # of Example: in NaCl the Na is +1 (Na+1Cl -1)
Group 2 metals found in compounds have an oxidation # of Example: in MgO the Mg is +2 (Mg+2O-2)

10. RULES FOR OXIDATION
4. Hydrogen, found in compounds, will have an oxidation # of +1, except when combined with metals to form metal hydrides; then their oxidation # is -1.
Examples: H2O the H is +1 (H+12O -2) HF the H is +1 (H+1F -1)
NaH the H is -1 (Na+1H -1)

11. RULES FOR OXIDATION
5. Oxygen, found in compounds, will have an oxidation # of -2, except in peroxides like H2O2 , where it is -1 or when combined with fluorine where it is +2.
Examples: H2O the O is -2 (H+12O-2)
H2O2 the O is -1 (H+12O-12)
OF2 the O is +2 (O+2F-12)
(Side Rule-NOTE:) F is ALWAYS -1

12. RULES FOR OXIDATION
6. In molecular or ionic compounds, the sum of the oxidation #s must equal zero.
Examples: H2O => 2 H+1 and 1 O -2 = (H+12O-2)
NaF => 1 Na+1 and 1 F -1 = (Na+1F-1)

13. RULES FOR OXIDATION Example: Sulfuric Acid => H2SO4
2 H+1 = +2 (see rule #4)
4 O -2 = (see rule #5)
therefore S must be +6 so that the sum of this molecule’s oxidation #s = zero.
(H+12S +6O-24)
2 ( +1) + ( +6) + 4 ( -2) = 0

14. RULES FOR OXIDATION
7. In polyatomic ions, the sum of the oxidation #s equals the charge on the ion.
Example: Ammonium ion => NH4+1
the H must be +1 (see rule #4)
4 H+1 = +4
The total charge of this ion is Therefore N must have a charge of -3.
4 ( +1) + ( -3) = +1

15. RULES FOR OXIDATION Example: Phosphate ion => PO4-3
the O must be -2 (see rule #5)
4 O-2 = -8.
The total charge of this ion is therefore P must have a charge of +5.
( +5) ( -2) = -3

16. OXIDATION NUMBERS Now you try some…
Find the oxidation #s of all the elements in the following substances:
H2CO3 Na2CO3 Mg(OH)2 PO NO2-1

17. OXIDATION NUMBERS Answers... H+1 2C+4 O-2 3 Na +1 2C +4 O -2 3
Mg +2(O -2 H +1 ) 2 Note (+2) + 2(-1) = 0
(P +5O -2 4) Note (+5) + 4(-2) = -3
(N +3O -2 2) Note (+3) + 2(-2) = -1

18. OXIDATION NUMBERS
That’s all folks….