1. AP Chem
This is our last unit!

2. A closer look at a selected reaction:
2 lost
2 gained
Oxidation: the loss of electrons by an atom or ion during a chemical reaction
Reduction: the gain of electrons by an atom or ion during a chemical reaction
Oxidation and Reduction occur together in a reaction. Oxidation-reduction reactions are known as Redox reactions.

3. Oxidation Numbers (state)
+, -, or neutral (0) numbers that can be assigned to atoms
Used to identify how many electrons are being lost or gained by an atom/ion when they form bonds

4. Assigning Oxidation Numbers: Rules
1. Free or Uncombined Elements (elements not bonded to another element) ALWAYS have an oxidation number of 0 2. Ions have the same oxidation number as the charge on the ion

5. Assigning Oxidation Numbers: Rules
3. When combined with another element:
Group 1 metal ions ALWAYS have an oxidation number of +1
Group 2 metal ions ALWAYS have an oxidation number of +2
Fluorine ion ALWAYS has an oxidation number of -1
4. Oxygen usually has an oxidation number of -2

6. Assigning Oxidation Numbers: Rules
Hydrogen’s oxidation number is different depending on whether it’s in an ionic or covalent compound
H bonded with a nonmetal (covalent): the oxidation number will be +1
H bonded with a metal (ionic): the oxidation number will be -1

7. Assigning Oxidation Numbers: Rules
6. The oxidation numbers must add up to the charge of the compound (0) or polyatomic ion

8. Assigning Oxidation Numbers: Practice+1 -1 -1 +2 -2 +1

9. Assigning Oxidation Numbers: Practice+1 +1 +6 -2 -2 +5 +4 -2 -2 +6 -2

10. In a redox reaction, one element loses electrons while another element gains electrons.
xidation
osing s
lectrons is
osing (electrons)
xidation
eduction
aining s
lectrons is
aining (electrons)
eduction

11. Writing Half Reactions+2 +2 2 2
Ca  Ca2+ + 2e-
Cr2+ + 2e-  Cr
CHARGES MUST BE BALANCED!

12. Writing Half Reactions+2 +2 2 2
Mg  Mg2+ + 2e-
Zn2+ + 2e-  Zn
CHARGES MUST BE BALANCED!

13. CHARGES MUST BE BALANCED!