How to Find Oxidation Number of an Atom

It’s crucial to understand what oxidation numbers are before learning how to find the oxidation number of an atom in a specific chemical.  The oxidation number, also called the oxidation state, is the charge that an atom would have if all of its interactions with other atoms were fully ionic. They describe how oxidised an atom in a chemical compound is. Integrals like positive, negative, and zero can be used to express the oxidation state conceptually.

In other terms, OS is a number that is allocated to elements in various chemical combinations. These values show the amount of electrons lost or acquired by the atom of an element in order to form a chemical connection with another element. It is used to determine the changes that occur in a redox reaction and is interchangeably used with the oxidation number. It has a numerical representation that is similar to valence electrons, however it is usually distinguished from formal charge.

Calculating Oxidation Numbers

The following rules can be used to assign an oxidation number to a particular element or compound.

• The oxidation number of any free element is 0

• Monatomic ions’ oxidation number is always equal to the net charge associated with the ion

• The oxidation state of the hydrogen atom (H) is +1. It has an oxidation number of -1 when linked with an element that has less electronegativity than it

• The oxidation state of oxygen is -2 in most of its molecules. The oxidation number corresponding to oxygen in peroxides, on the other hand, is -1

• In their compounds, all alkali metals (group 1 elements) have an oxidation state of +1

• In their compounds, all alkaline earth metals (group 2 elements) have an oxidation state of +2

• A halogen (group 17 element) is assigned an oxidation number of -1 in compounds made up of two elements

• The sum of all the oxidation numbers of the constituent atoms in neutral substances equals zero

• When considering polyatomic ions, the net charge of the polyatomic ion is equal to the sum of all the oxidation numbers of the atoms that make it up

With the procedures outlined above, the oxidation number of an atom in a particular chemical can be computed.

Examples

The oxidation states of each individual atom in certain sample compounds are determined below:

Hydrochloric Acid (HCl)

• The oxidation state of a group 17 element (halogen) in a diatomic molecule is -1, according to the criteria stated above. It is also mentioned that unless it is paired with a less electronegative element, hydrogen always has an oxidation number of +1.

• Because chlorine is more electronegative than hydrogen, the hydrogen atom in HCl has an oxidation number of +1.

• In HCl, the oxidation number of hydrogen is +1, while the oxidation number of chlorine is -1. By adding these oxidation numbers, these values can be validated. The numbers are validated since the sum is zero, which is the value of the oxidation number corresponding to a neutral molecule.

Carbon Dioxide (CO2)

• The oxidation number of oxygen in its compounds (excluding peroxides) is -2, according to the principles for calculating oxidation numbers, which may be found in the previous subsection.

• Because carbon dioxide has two oxygen atoms, the total of the oxidation numbers corresponding to each oxygen is -4.

• The carbon atom must have an oxidation state of +4 since the CO2 molecule is neutral (the sum of all the oxidation numbers in a neutral molecule is zero).

• As a result, the oxidation state of oxygen in a carbon dioxide molecule is -2, while the oxidation number of carbon is +4

Chlorine oxidation state in KCl

Because KCl is neutral, its net charge is zero.

KCl oxidation state = potassium oxidation state + chlorine oxidation state = 0.

Potassium oxidation state = +1

+1 + x = 0: x = -1 Oxidation states

K Cl are atoms in the species

Chlorine oxidation state in KCl = -1

Cl2O:

Cl2O is neutral, hence its net charge is zero.

Cl2O net oxidation state = 2 x chlorine oxidation state + 1 x oxygen oxidation state = 0.

The oxygen oxidation state is -2.

2 x + (-2) = 0: x = +1 Oxidation states

2Cl O atoms in the species

Chlorine oxidation state in Cl2O= +1

Conclusion

The charge that an atom would have in a molecule if all of the bonding electrons were assigned to the more electronegative element is known as its oxidation number. The oxidation number of an atom increases as a result of oxidation. The oxidation number of an atom is reduced during reduction. To calculate oxidation state we follow above -mentioned rules.