1. Oxidation-Reduction Reactions
REDOX
Oxidation-Reduction Reactions

2. Oxidation-Reduction Reactions
Electrons transferred 1 atom to another
Redox reactions:
All single-replacement rxns
All combustion rxns

3. LEO GOES GER!!!

4. Oxidation
= loss of electrons
LOSS of ELECTRONS = OXIDATION
LEO

5. Reduction
= gain of electrons
GAIN of ELECTRONS = REDUCTION
GER

6. REDOX Oxidation & Reduction: complementary reactions
occur together & simultaneously or not at all

7. Oxidation Numbers In Ionic Compounds:
# of electrons lost/gained by atom determined by ions that form compound

8. Assigning Oxidation Numbers

9. # of free, uncombined element = 0
Rule #1:
# of free, uncombined element = 0
Na He O2 N2 S8 Cl2 P

10. # of monatomic ion = charge of ion
Rule # 2:
# of monatomic ion = charge of ion
Ca+2 = Cl-1 = Al+3 = +3
Remember: Ions form ionic cmpds:
CaCl2, Al(NO3)3, etc.

11. Rule # 3:
F always -1
CF4

12. Rule # 4:
H is nearly always +1
except if bonded to metal then -1
H2O, HNO3, H2SO4, LiH, CaH2, NaH

13. O is nearly always -2 except when:
Rule # 5:
O is nearly always -2 except when:
OF2
- Bonded to F: O is +2
O22-
Bonded to peroxide ion: O is -1
(group 1 & 2 metals)

14. Rule # 6
Sum oxidation # in neutral compound = 0
H2O CO2 NO SO3

15. Rule # 7
Sum oxidation # in polyatomic ion =
charge of ion
Sum in SO4-2 = -2
Sum in NO3-1 = -1

16. Rule # 8
Covalent cmpds:
oxidation # more electronegative atom =
negative charge if was ion
*NH3: N = -3, H = +1
SiCl4: Si = +4, Cl = -1

17. Assign Oxidation Nos KCl K = +1, Cl = -1 CaBr2 CO Ca = +2, Br = -1 CO2
Al(NO3)3
Na3PO4
H2S
NH4+1
SO3-2
K = +1, Cl = -1
Ca = +2, Br = -1
C = +2, O = -2
C = +4, O = -2
Al = +3, O = -2, N = +5
Na = +1, O = -2, P = +5
H = +1, S = -2
N = -3, H = +1
S = +4, O = -2

18. 2) And if you’re lucky you strike oil & it shoots up4 3 2 1 -1 -2 -3 -4
2) And if you’re lucky you strike oil & it shoots up
1) You dig down with an oil rig

19. Electrons are Negative!
Why use the word “reduced” when electrons are gained?
Look at how the oxidation number changes
Ex: Cl gains an electron → Cl-1
oxidation # ↓ from 0 to -1; the # was reduced

20. Writing Equations
Even though oxidation & reduction reactions occur together we write separate equations for each process
known as Half-Reactions

21. Reduction Half-Reactions
I e-  2I-1
O e-  2O-2
Half-reactions must demonstrate:
conservation of mass & conservation of charge
# atoms on left must = # atoms on right
total charge on left must = total charge on right
Electrons are gained so put
on reactant side!

22. Oxidation Half-reactions
K  K e-
Fe2+  Fe e-
Cu  Cu e-
Total Charge on left = Total Charge on right
# atoms on left = # atoms on right
Electrons are lost so they are put on product side!

23. Vocabulary Interlude Oxidizing Agent: Substance being reduced
Accepts electrons from something else
aids oxidation for another species
Reducing Agent: Substance being oxidized
Loses electrons to something else
aids reduction for another species