Oxidation States Explained+ Interactive Calculator
Oxidation states describe the degree of oxidation (loss of electrons) of an atom in a chemical compound. Use our dynamic calculator and comprehensive rules guide below to easily calculate oxidation states and master redox reactions.
Common Oxidation States
Valence Electrons
8
Electronegativity
1.83
Group
8
Block
D-block
What this means for Iron
The oxidation states of Iron (Fe) indicate how many electrons it typically gains, loses, or shares when forming a chemical bond.
Loses or shares 3 electrons
Acts as a reducing agent (is oxidized)
Loses or shares 2 electrons
Acts as a reducing agent (is oxidized)
Oxidation States Explorer
Click Any Element
Hover over an element to see its common oxidation states.
Practical Examples
Notable Oxidation States
See how the primary oxidation states behave for commonly researched elements.
Hydrogen Oxidation States
Hydrogen (H) primarily exhibits oxidation states of +1, -1. With 1 valence electrons, its chemistry is determined by its ability to lose electrons.
Carbon Oxidation States
Carbon (C) primarily exhibits oxidation states of +4, +2, -4. With 4 valence electrons, its chemistry is determined by its ability to gain electrons.
Nitrogen Oxidation States
Nitrogen (N) primarily exhibits oxidation states of +5, +4, +3, +2, +1, -1, -2, -3. With 5 valence electrons, its chemistry is determined by its ability to gain electrons.
Oxygen Oxidation States
Oxygen (O) primarily exhibits oxidation states of -2, -1. With 6 valence electrons, its chemistry is determined by its ability to gain electrons.
Phosphorus Oxidation States
Phosphorus (P) primarily exhibits oxidation states of +5, +3, -3. With 5 valence electrons, its chemistry is determined by its ability to lose electrons.
Sulfur Oxidation States
Sulfur (S) primarily exhibits oxidation states of +6, +4, +2, -2. With 6 valence electrons, its chemistry is determined by its ability to gain electrons.
Chlorine Oxidation States
Chlorine (Cl) primarily exhibits oxidation states of +7, +5, +3, +1, -1. With 7 valence electrons, its chemistry is determined by its ability to gain electrons.
Vanadium Oxidation States
Vanadium (V) primarily exhibits oxidation states of +5, +4, +3, +2. With 5 valence electrons, its chemistry is determined by its ability to lose electrons.
Chromium Oxidation States
Chromium (Cr) primarily exhibits oxidation states of +6, +3, +2. With 6 valence electrons, its chemistry is determined by its ability to lose electrons.
Manganese Oxidation States
Manganese (Mn) primarily exhibits oxidation states of +7, +4, +3, +2. With 7 valence electrons, its chemistry is determined by its ability to lose electrons.
Iron Oxidation States
Iron (Fe) primarily exhibits oxidation states of +3, +2. With 8 valence electrons, its chemistry is determined by its ability to lose electrons.
Copper Oxidation States
Copper (Cu) primarily exhibits oxidation states of +2, +1. With 11 valence electrons, its chemistry is determined by its ability to lose electrons.
A. What Are Oxidation States?
To understand exactly what is oxidation state, imagine an accounting system tracking the flow of electrons between atoms. The oxidation state (or oxidation number) represents the hypothetical electrical charge an atom would possess if all its bonds to different elements were considered to be 100% ionic.
In reality, covalent bonds share electrons, but the oxidation state model exaggerates this sharing: it gives the bonding electrons completely to the more electronegative atom. This simplifies complex chemistry, allowing chemists to easily track which atoms gain, lose, or share electrons during a reaction.
Core Principles
- ✔ A positive oxidation state means the atom has lost (or is hypothetically stripped of) electrons.
- ✔ A negative oxidation state means the atom has gained (or forcefully holds) electrons from a less electronegative atom.
- ✔ A zero oxidation state indicates a pure element where atoms share electrons equally.
The Geometric Factor: Atomic Radius
The ease with which an atom reaches a specific oxidation state is fundamentally dictated by its Atomic Radius.
Large Radius = Easy Oxidation
Atoms with a large radius (like Alkali metals) have valence electrons far from the nucleus, resulting in low ionization energy and frequent +1 or +2 oxidation states.
Small Radius = Strong Reduction
Compact atoms (like Fluorine or Oxygen) have a massive nuclear pull on their outer shells, allowing them to forcefully gain electrons into negative oxidation states.
Think of an atom as a bank account. Its valence electrons represent its initial balance. When it bonds, it might "lend" electrons (entering a positive balance/oxidation state) or "borrow" electrons (entering a negative balance). A molecule is simply a group of accounts where all lending and borrowing nets out to the precise charge of the molecule. This concept forms the cornerstone of predicting oxidation and reduction reactions.
B. Rules for Determining Oxidation States
Mastering the oxidation state rules is crucial for solving any chemical equation. These rules operate in a strict hierarchy. If two rules ever conflict, the rule higher up the list takes precedence.
Elements in their Free State
Any pure element uncombined with other elements has an oxidation state of 0. Examples: O₂, H₂, S₈, Fe(s).
Monatomic Ions
The oxidation state of a monatomic ion simply equals its net charge. Example: Na⁺ is +1, Cl⁻ is -1.
The Sum of States
The sum of all oxidation states in a neutral molecule is 0. In a polyatomic ion, the sum equals the ion's charge. Example: In H₂O, 2(H) + (O) = 0. In SO₄²⁻, (S) + 4(O) = -2.
Fluorine
Fluorine is the most electronegative element, so it is always -1 in its compounds.
Alkali & Alkaline Earth Metals
Group 1 metals (Li, Na, K...) are always +1 in compounds. Group 2 metals (Mg, Ca, Ba...) are always +2.
Hydrogen
Hydrogen is almost always +1. Exception: when bonded to metals in hydrides (like NaH), it takes an electron and becomes -1.
Oxygen
Oxygen is usually -2. Exceptions: In peroxides (like H₂O₂), it is -1. When bonded to fluorine (like OF₂), oxygen can be positive (+2).
C. How to Calculate Oxidation States
Wondering how to calculate oxidation state? It's simply a matter of applying the rules above using basic algebra. Let's walk through three distinct examples ranging from simple compounds to complex polyatomic transition metal complexes.
Example 1: Carbon Dioxide (CO₂)
- Identify knowns: Oxygen is almost always -2.
- Setup the equation: C + 2(O) = 0.
- Substitute: C + 2(-2) = 0.
- Solve: C - 4 = 0 → Carbon is +4.
Example 2: Permanganate Ion (MnO₄⁻)
- Identify knowns: Oxygen is -2.
- Net charge: The whole ion equals -1.
- Setup: Mn + 4(O) = -1.
- Solve: Mn + 4(-2) = -1 → Mn - 8 = -1 → Manganese is +7.
Example 3: Potassium Dichromate (K₂Cr₂O₇)
Often needed to figure out how to find oxidation states of transition metals like Chromium in large salts.
- Knowns: Potassium (Group 1) is +1. Oxygen is -2.
- Net charge is 0.
- Setup: 2(K) + 2(Cr) + 7(O) = 0.
- Substitute: 2(+1) + 2(Cr) + 7(-2) = 0.
- Solve: 2 + 2(Cr) - 14 = 0 → 2(Cr) = 12 → Chromium is +6.
D. Oxidation vs Reduction
It is impossible to discuss oxidation states without discussing redox. Oxidation vs reduction represents two halves of the same chemical coin. Electrons must come from somewhere and go somewhere; they are never isolated in a void. Therefore, when one element loses electrons, another must gain them.
Oxidation
Oxidation Is Loss (OIL)
- Loss of electrons.
- An increase in oxidation state.
- The element is the reducing agent.
- Example: Fe(0) → Fe(+3) + 3e⁻
Reduction
Reduction Is Gain (RIG)
- Gain of electrons.
- A decrease in oxidation state.
- The element is the oxidizing agent.
- Example: O₂(0) + 4e⁻ → 2O(-2)
In oxidation and reduction reactions (redox reactions), comparing the oxidation states of reactants versus products allows you to instantly identify which species was oxidized and which was reduced. For example, in the rusting of iron: 4 Fe + 3 O₂ → 2 Fe₂O₃
Iron goes from 0 to +3 (loss of electrons = Oxidation). Oxygen goes from 0 to -2 (gain of electrons = Reduction).
E. Practical Applications of Oxidation States
The oxidation numbers framework isn't just an abstract system. It dictates the design of the physical world spanning energy capture, biological survival, and industrial manufacturing.
Lithium-Ion Batteries
Batteries work solely by forcing electrons from an oxidized metal anode through an external circuit to a reduced metal-oxide cathode. The shifts in oxidation states (e.g. Cobalt from +4 to +3) power modern devices.
Cellular Metabolism
Cellular respiration is a massive redox chain. Food (carbon) gets heavily oxidized while oxygen gets reduced to water, capturing the electron energy released to synthesize ATP.
Corrosion & Rust
Rust occurs when iron is slowly oxidized by atmospheric oxygen. Protective sacrifical anodes (like Zinc) are used because their oxidation state is more readily shifted, protecting the iron skeleton.
Catalysis
Transition metals like Rhodium or Palladium are used in catalytic converters because they transition smoothly between multiple oxidation states rapidly, reducing toxic car emissions (NOx to N2).
F. Common Mistakes & FAQs
What are multiple oxidation states in elements?
How to find oxidation states of transition metals?
How does oxidation number change in reactions?
Can oxidation states be fractions?
What is the highest known oxidation state?
Master the Atom
Understanding oxidation states is just the beginning. Connect this knowledge with orbital structures and electron shells.
Scientific References & Citations
Toni Tuyishimire
Toni is specialized in high-performance computational tools and complex STEM visualizations. Through Toni Tech Solution, he architects scientifically accurate, deterministic software systems designed to educate and empower global digital audiences.