Oxidation and Reduction (aka REDOX reactions)
Historically…
Reduction was about making a metal from a compound:
Fe2O3 + CO  2Fe + 3CO2 (iron is reduced)
And, oxidation was the term to describe the reaction of a
substance with oxygen (combustion or corrosion)
2Mg + O2  2MgO
…but things have changed
The Electron Transfer theory:
All reactions are a combination of 2 parts (half-reactions)
Take a closer look at the reaction of magnesium above:
-both reactions are balanced by mass and by charge (the number
of electrons lost by one atom is gained by the other)
-The oxygen atom has gained electrons (it is reduced and is the
oxidizing agent)
-The magnesium atom has lost electrons (it is oxidized and is the
reducing agent)
LEO the lion says GER !!!!!!!!
An introduction to writing and balancing half-reactions:
Example:
Write and label 2 balanced half-reaction equations to describe
the reaction of zinc metal with aqueous lead (II) nitrate shown
below:
Zn + Pb(NO3)2  Pb + Zn(NO3)2
Example:
Write and label 2 balanced half-reaction equations to describe
the reaction of copper metal with aqueous silver nitrate as shown
below:
Cu + Ag NO3  Ag + Cu(NO3)2
Oxidation Numbers
An oxidation number is the charge that an atom in a compound
would have if the electron pair in the bond belonged solely to the
more electronegative atom.
RULES:
1. The oxidation number for any atom in an element is zero (0).
2. The oxidation number of a monatomic ion is equal to the charge
on the ion.
3. The oxidation number of each hydrogen atom in most of its
compounds is +1.
4. The oxidation number of each oxygen atom in most of its
compounds is -2.
5. In compounds, the elements of Group 1, Group 2, and aluminium
have positive oxidation numbers of +1, +2, and +3, respectively.
**VERY IMPORTANT: The sum of the oxidation numbers of all
the atoms must be equal the apparent charge of that particle **
Example 1:
Find the oxidation # of chlorine in Cl2
Example 2:
Find the oxidation number for each atom in SCl2
Example 3: What is the oxidation # of Mn in MnO4 – ?
Example 4: What is the oxidation number of sulfur in Na2SO4?
Example 5: identify which elements are being oxidized and which
are being reduced when natural gas (methane) burns in a furnace
(assume complete combustion)