1. Oxidation and Reduction

2. Introduction to Oxidation and Reduction
Early attempts to define oxidation and reduction were based on observations of the gain and loss of oxygen and hydrogen during a chemical change.
These definitions are still useful in some cases, particularly in organic chemistry, but they have largely been replaced by a more inclusive approach.
Oxidation
Reduction
Gain of oxygen
Loss of oxygen
Loss of hydrogen
Gain of hydrogen

3. Oxidation and Reduction
Oxidation and Reduction are now defined as the transfer of electrons .
Oxidation is the loss of electrons and Reduction is the gain of electrons (OILRIG)
Oxidation and reduction will always occur together.
Reactions of this type are called REDOX reactions

4. Oxidation and Reduction

5. Oxidation States
Oxidation states can be used to track oxidation change.
Oxidation state is the value assigned to each atom in a compound and it is a measure of the electron control or possession it has relative to the atom in the pure element.
Oxidation state enables us to keep track of the relative electron density in a compound and how it changes during a reaction.
There are two parts to the oxidation state:

8. Interpreting Oxidation States
The element sulfur can have a wide range of oxidation states in different compounds.
The more positive the oxidation state is, the more the atom has lost control over the electrons, so the more oxidized it is.
The more negative the oxidation state is, the more the atom has gained control over electrons, so the more reduced it is.
Therefore, H2S represents sulfur in its most reduced form and SO3 and H2SO4 represent sulfur in its most oxidized form.
So, by keeping track of the oxidation states, one can determine which species was reduced and which was oxidized; an increase in oxidation state means oxidation and a decrease in oxidation number means reduction.

10. Naming Compounds Using Oxidation Numbers

12. Writing Half-Equations
A redox reaction can be separated into the two processes – oxidation and reduction.
These are called half-equations.
Electrons are added on one side of each equation to balance the charges.

13. Writing Half-Equations

14. Balancing Redox Equations