Oxidation Number
Definition and meaning of Oxidation Number in chemistry.
An oxidation number is a formal numerical value assigned to an element in a chemical compound that represents the total number of electrons lost or gained by an atom of that element.
In more detail
Oxidation numbers are systematically used by chemists to keep track of electron transfers occurring during complex redox reactions. They indicate the hypothetical electrical charge an atom would possess if all of its chemical bonds to atoms of different elements were assumed to be completely ionic. A mathematical increase in an atom's oxidation number indicates oxidation, while a corresponding decrease in the oxidation number indicates reduction.
Key facts
| Field | General Chemistry |
|---|---|
| Formula | H2O |
| Purpose | Tracking electrons in redox reactions |
| Rule | Pure elements in their free state always have an oxidation number of zero |
In a molecule of water (H2O), the oxidation number of the central oxygen atom is always -2, while the oxidation number of each individual hydrogen atom is +1.
Frequently asked questions
What is the official oxidation number of an uncombined elemental substance?
The oxidation number of any atom in its pure elemental form, such as solid sodium or diatomic oxygen gas, is defined as exactly zero.