Difference Wiki

Oxidation Number vs. Oxidation State: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on November 25, 2023
Oxidation number is a formalism assigning charges to atoms, while oxidation state reflects an atom's actual electron loss or gain in a compound.

Key Differences

Oxidation number, a concept in chemistry, represents the charge an atom would have if electrons were completely transferred. Oxidation state, on the other hand, describes the degree of oxidation of an atom in a chemical compound.
The oxidation number is often used in ionic compounds where electron transfer is clear-cut. The oxidation state is more nuanced, reflecting the shared electrons in covalent bonding.
While determining the oxidation number, an assumption is made that the compound consists of ions. In contrast, the oxidation state considers the real-world scenario where electrons are not always completely transferred but shared.
Oxidation numbers are typically integers, but oxidation states can be fractions to denote average oxidation states in compounds with shared electrons.
In simple ions, the oxidation number and oxidation state are the same. However, in more complex molecules, the oxidation state provides a more accurate representation of electron distribution.

Comparison Chart


Hypothetical charge on an atom assuming complete electron transfer.
Real electron loss or gain by an atom in a compound.

Use in Compounds

More straightforward in ionic compounds.
More accurate in covalent compounds with shared electrons.

Numerical Nature

Often integers.
Can be fractions to represent shared electron scenarios.

Electron Transfer Assumption

Assumes complete electron transfer.
Reflects actual electron sharing or transfer.

Representation in Simple Ions

Same as oxidation state.
Same as oxidation number.

Oxidation Number and Oxidation State Definitions

Oxidation Number

The hypothetical charge an atom would have in a molecule or compound if electrons were completely transferred.
In NaCl, the oxidation number of Na is +1.

Oxidation State

Indicates the degree of electron sharing in bonds between different atoms.
In water (H2O), oxygen has an oxidation state of -2.

Oxidation Number

A tool used in balancing chemical equations.
The oxidation number helps in identifying the reducing and oxidizing agents in a reaction.

Oxidation State

Useful in understanding redox reactions in complex molecules.
Oxidation states help in analyzing the electron flow in redox reactions.

Oxidation Number

The apparent charge of an atom within a molecule or ion.
In H2O, hydrogen has an oxidation number of +1.

Oxidation State

A description of the degree of oxidation (loss of electrons) of an atom in a chemical compound.
In CO2, the oxidation state of carbon is +4.

Oxidation Number

A theoretical charge determining an atom's electron-donating or accepting capability.
The oxidation number of chlorine in NaCl is -1.

Oxidation State

Reflects the sharing of electrons between atoms in covalent bonding.
The oxidation state of sulfur in H2SO4 can vary depending on its bonding.

Oxidation Number

A number assigned to an element in chemical combination that represents the number of electrons lost or gained.
Oxygen usually has an oxidation number of -2.

Oxidation State

The actual state of an atom as defined by the number of electrons it has lost or gained.
The oxidation state of iron in Fe2O3 is +3.


What's the primary difference between oxidation number and oxidation state?

Oxidation number is a hypothetical charge, while oxidation state reflects actual electron loss or gain.

Are oxidation numbers always whole numbers?

Yes, they are typically whole numbers.

Do oxidation number and state always match?

They match in simple ions but can differ in complex molecules.

How is the oxidation state determined in a molecule?

By considering the real electron sharing between atoms.

Can the oxidation state of an element vary in different compounds?

Yes, it varies based on the compound and its bonding.

Can oxidation states be fractional?

Yes, oxidation states can be fractional in compounds with shared electrons.

Is the oxidation number used in balancing redox reactions?

Yes, it helps in identifying oxidizing and reducing agents.

Does the oxidation number change during a redox reaction?

Yes, it changes reflecting electron loss or gain.

How does the oxidation state help in understanding chemical reactions?

It helps to track electron flow in redox reactions.

Are oxidation number and state important in organic chemistry?

Yes, particularly in understanding electron transfer and bonding.

Can hydrogen have different oxidation numbers?

Yes, typically +1, but -1 in hydrides.

Is oxidation state considered in ionic bonding?

Yes, especially to determine electron distribution.

Are there exceptions to assigning oxidation numbers?

Yes, certain rules and exceptions apply, like in coordination compounds.

How do you determine the oxidation number in a polyatomic ion?

By summing up the charges of the constituent atoms.

Is the oxidation number applicable to all elements in the periodic table?

Generally yes, but its assignment follows specific rules for each element.

Is it possible for the oxidation number to be negative?

Yes, it can be negative if the atom gains electrons.

Does the oxidation number affect the chemical properties of an element?

It influences its electron-donating or accepting behavior.

How is the oxidation state of oxygen generally represented?

Usually as -2, except in peroxides.

Can the oxidation state be zero?

Yes, in elemental forms of atoms.

Can an atom have different oxidation states in the same molecule?

Yes, in complex molecules with multiple bonding scenarios.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

Trending Comparisons

Popular Comparisons

New Comparisons