Chemistry class 12th Oxidation_States_Class12

Oxidation States - Class 12 Chemistry


1. Introduction to Oxidation States
Oxidation state (or oxidation number) is the charge an atom would have if electrons were completely
transferred in a compound. It helps in understanding redox reactions and electron distribution.


2. Rules for Determining Oxidation States
- The oxidation state of a free element is always 0.
- The oxidation state of a monoatomic ion is equal to its charge.
- Oxygen usually has an oxidation state of -2, except in peroxides (-1) and superoxides (-1/2).
- Hydrogen is +1 when bonded to nonmetals and -1 when bonded to metals.
- The sum of oxidation states in a neutral compound is 0, and in a polyatomic ion, it equals the ion's
charge.


3. Oxidation States of Different Elements
- Alkali metals (Group 1): Always +1.
- Alkaline earth metals (Group 2): Always +2.
- Halogens: Usually -1, but can be positive in compounds with oxygen.
- Transition metals: Show variable oxidation states due to d-orbital involvement.


4. Variable Oxidation States
Some elements exhibit multiple oxidation states. Example:
- Iron (Fe): +2, +3
- Copper (Cu): +1, +2
- Manganese (Mn): +2, +4, +7
These variations arise due to the involvement of d-electrons in bonding.


5. Oxidation and Reduction Reactions
- **Oxidation:** Increase in oxidation state (loss of electrons).
- **Reduction:** Decrease in oxidation state (gain of electrons).
Example: In the reaction Zn + Cu2+ -> Zn2+ + Cu, Zn is oxidized and Cu2+ is reduced.


6. Applications of Oxidation States