1. Redox Rules to Learn For Ionic and Covalent bonds

2. Electronegativity and Redox Rules
Definition: Electonegativity is the atom’s ability to attract electrons.
Fluorine is the most electronegative element

3. Electronegativity Trend
Increase EN
More protons to attract electrons
Decrease EN
electrons get further away from protons

4. Rule #1
Oxidation number of an uncombined atom = zero (no compounds or ions) i.e . Mg, H2, Na ie. All H2 O2 N2 Cl2 Br2 I2 F2 ’s ox. # are zero

5. Rule #2
Oxidation number of a monatomic ion = charge of the ion i.e. Mg2+ , O2- , Al3+ , Br- +2 -2 +3 -1

6. Rule #3
The sum of the oxidation numbers of a neutral compound = 0 i.e. H2O CO2 CO NaCl +1 -1 +1 -2 +4 -2 +2 -2
2(+1)
- 2 = 0
4 +
2(-2)
= 0 =0 =0

7. Rule #4
The oxidation number for H is +1 Exception: when bonded to a less electronegative element (metal), then it is -1. i.e. LiH, NaH, MgH2 Exception i.e. HF, HCl +1 -1 +1 -1 +2 -1 +1 -1 +1 -1

8. Rule#5 Two exceptions: peroxides and fluorine in H2O2 with OF2
Oxygen’s oxidation number is -2, in a compound
Two exceptions: peroxides and fluorine
in H2O2
with OF2 +1
? = -1
where O is -1
2(+1)
+ 2( ?) = 0 +2 -1
where O is +2
? = 0
2(-1)
fluorine (more electronegative)

9. Rule#6 Oxidation number of polyatomic compound = zero
polyatomic ion = the charge of the ion
i.e. compounds:
NH3 SiCl4 K3PO4
i.e. ions:
NH4+ CO32- SO42- NO3- -3 +1
= 0
3(+1) -3 +1
= +1
4(1)

10. Rule#7
Oxidation numbers for metals in: Group 1A metal compound +1 2A metal compound +2 3A Aluminum compound +3 i.e. NaCl MgSO4 AlPO4 +1 -1 +2 +6 -2 +3
+2 + ? + 4(-2)
= 0
= 0
= 0

11. Rule #8
The most electronegative element fluorine ALWAYS has an oxidation number of -1 when it is bonded to another element.
i.e. HF

12. Question Time Assign oxidation numbers to each element Cl2 Cl- MgCl2
NaH
HCl
K3PO4
CaSO4 KF

13. Using the Rules Oxidation Number
If oxidation number goes up it is oxidized.
If oxidation number goes down it is reduced.

14. Using the Rules-Last Lesson
Balance the reactions,
write the oxidation numbers for each atom
and write the oxidizing and reducing agents.
Ex1 HCl + Zn  ZnCl2 + H2
Loss of electron oxidation (LEO)
Reducing agent +1 -1 +2 -1 2 =0
2(-1)
Gain of electron reduction (GER)
Oxidizing agent

15. Using the Rules
Ex2 Mg + N2  Mg3N2 Ex3 H2S + Cl2  HCl + S Ex4 Fe + O2  Fe2O3

16. Summary of Oxidation/Reduction
There are three definitions of oxidation and reduction:
Oxidation Reduction
Losing of electrons (LEO)
Gaining of electrons (GER)
Increasing oxidation #
Decreasing oxidation #
Gaining oxygen
Losing oxygen

17. Two ways to remember oxidation/reduction (redox) is:
L E O goes G E R O I L R I G
X I D AT I O N O S E L E C T R O N S S
E D U C T I O N
X I D AT I O N
AIN L E C T R O N S
E D U C T I O N
O S I N G S
A I N I N G