Redox Reactions of
Nonmetals
Read pp. 379-383
Redox and Non-Metals
• Redox rxns can involve non-metals!
– Eg. burning of fossil fuels result in sulfur (S)
and oxygen gas (O2), which are both nonmetals, forming SO2 (sulfur dioxide)
– However, redox rxns involves knowing the
oxidation numbers (+, -, 0). Harder to do with
non-metals!
• Sulfur and oxygen are both commonly
known to have a charge of -2
• How do we do this with SO2?
• This is where we use the rules of
oxidation numbers…
Oxidation Numbers (ONs)
• Ion charges and ONs are not the
same thing!
• Oxidation number = + or - number
corresponding to the theoretical
charge that an atom in a molecule or
ion would have if the electron pairs
in covalent bonds belonged entirely to
the more electronegative atom
• ONs are based on set rules
• The sum of all ONs of the atoms in a
compound must equal ZERO
• The sum of all ONs of the atoms in a
polyatomic ion must equal its charge
Going back to the SO2 example:
Which is more electronegative?
Oxygen is more EN than sulfur (3.2 vs 2.5), so the
charge for oxygen will be -2
SO2
Rules for Oxidation Numbers
1.
Elements
•
2.
Elements on their own are always 0
Group I and II
•
•
3.
Elements on their own are always 0
Group I is +1; Group II is +2
Simple and Polyatomic Ions
•
•
4.
The charge on the simple ion is the oxidation number
The sum of ONs in a polyatomic ion must equal the charge on the ion
Hydrogen
•
•
5.
Usually +1
When bonded to Group I or Group II, becomes -1
Oxygen
•
•
•
6.
Usually -2
O2 is 0
Peroxide’s (H2O2) oxygen atoms are -1
Fluorine
•
•
Always -1
Other halogens (Cl, Br, I) are usually -1, except when bonded to
oxygen
Examples – Find ON for each atom
• H2
H=
• Fe2O3
Fe =
O=
• KMnO4
K=
Mn =
• SO42-
S=
O=
• Cr2O72-
Cr =
O=
O=
Worksheet 1 – Assigning
Oxidation Numbers
For each element:
• Hg
• FeO
• F• O2
• PbI2
• NiO
• Al2O3
• K2Cr2O7
For bolded elements:
• HClO3
• SO32• CaCO3
• MnO4• Na2CO3
• PbSO4
• KClO3
• CrO32-
Redox Practice Worksheet
For the following reaction, provide:
• Oxidation numbers for all of the elements
• Which elements were oxidized and
reduced
FeO + Al  Al2O3 + Fe
FeO + Al  Al2O3 + Fe
2Na + FeCl2  2NaCl + Fe
2C2H2 + 5O2  4CO2 + 2H2O
2PbS + 3O2  2SO2 + 2PbO