What oxidation states can carbon have?

Carbon can have any integer oxidation state from −4 to +4. The most common are −4 (in alkanes like methane), 0 (in elemental carbon such as graphite or diamond), +2 (in carbon monoxide), and +4 (in CO₂ and carbonates). Intermediate states appear in compounds like formaldehyde (0), formic acid (+2), and ethanol (−2/−1 per carbon, averaged).

How do you calculate the oxidation state of carbon in a compound?

Assign −2 to each oxygen and +1 to each hydrogen (in most organic/inorganic compounds), then solve for the carbon oxidation state so the total charge of the molecule or ion equals zero (or the known ionic charge). For example, in CO₂: x + 2(−2) = 0, so x = +4.

Why does carbon have so many oxidation states?

Carbon sits in the middle of the electronegativity scale (2.55 Pauling) and has four valence electrons — exactly half a full octet. It can either donate up to four electrons (→ +4) or accept up to four electrons (→ −4), making every intermediate state energetically accessible depending on the bonding partner.

What is the oxidation state of carbon in methane (CH₄)?

In CH₄, hydrogen is +1. The overall molecule is neutral, so C + 4(+1) = 0, giving carbon an oxidation state of −4. This is the most reduced state carbon can achieve and is found in all saturated hydrocarbons and carbides like Al₄C₃.

What is the oxidation state of carbon in carbon monoxide (CO)?

In CO, oxygen is −2 and the molecule is neutral, so C + (−2) = 0, giving carbon +2. This is one of the few stable +2 carbon species outside of organic chemistry.

Does carbon form a +4 ion like other elements?

No. Carbon does not form a discrete C⁴⁺ ion under ordinary conditions — the fourth ionization energy is extremely high (~64,492 kJ/mol total for all four). Carbon achieves the formal +4 oxidation state only through covalent bonding (as in CO₂), never as a bare quadruply-charged cation.

What is the oxidation state of carbon in organic compounds?

It varies with each functional group. Alkane carbons are near −4 to −2; alcohol carbons are around −1; aldehyde carbons are near 0 to +1; carboxylic acid carbons are +3; and CO₂/carbonate carbons are +4. Complex molecules often have multiple carbon atoms, each at a different oxidation state.

Carbon Oxidation States

Name: Carbon Oxidation States
Availability: InStock
Author: Nham Vu

Reference tool covering all carbon oxidation states from −4 to +4, with compound examples, electron configuration, and an interactive oxidation state identifier.

Atomic # 6 C Carbon

Atomic Mass

12.011 u

Group

14 (IVA)

Period

Block

p-block

Electronegativity

2.55 (Pauling)

Oxidation States

−4, −3, −2, −1, 0, +1, +2, +3, +4

Carbon has the ground-state configuration [He] 2s² 2p², giving it four valence electrons. Because it sits at the midpoint of the electronegativity scale, carbon can either donate (up to +4) or accept (down to −4) electrons, resulting in a uniquely wide range of accessible oxidation states compared to most elements.

State	Stability	Example	Notes
-4	Highly stable (in carbides/alkanes)	CH₄, Al₄C₃	Most reduced state. Carbon gains 4 electrons formally. Found in methane and ionic carbides.
-3	Common (organic)	C₂H₆ (each C)	Ethane: each carbon bonded to 3 H and 1 C. Common in long alkane chains.
-2	Common (organic)	CH₂O (if bonded to 2 H)	Seen in portions of alcohols, ethylene, and other saturated organic molecules.
-1	Common (organic)	C₂H₂ (acetylene)	Acetylene: each carbon bonded to 1 H and the other carbon via triple bond.
0	Common (elemental & organic)	C (graphite), HCHO (formaldehyde)	Elemental carbon. Also the state in formaldehyde and certain symmetric molecules.
+1	Uncommon	Glyoxal (CHO-CHO)	Rare; found in specialized organic compounds like glyoxal or certain carbenes.
+2	Stable (inorganic)	CO (carbon monoxide)	Carbon monoxide is the classic +2 species; also seen in some metal carbonyls.
+3	Common (organic)	HCOOH (formic acid)	Found in carboxylic acids, aldehydes oxidized one step further. Formic acid: +2; acetic acid methyl C: −3.
+4	Highly stable (inorganic)	CO₂, CaCO₃, CCl₄	Most oxidized state. Carbon dioxide, carbonates, and tetrachloromethane all have carbon at +4.

Ionization Energies
IE₁ = 1086.5 kJ/mol | IE₂ = 2352.6 kJ/mol | IE₃ = 4620.5 kJ/mol | IE₄ = 6222.7 kJ/mol
All four valence electrons can be lost in principle, but carbon never forms a C⁴⁺ ion — it reaches +4 through covalent bonding only.

Carbon's oxidation state changes dramatically across functional groups. The table below covers common inorganic and organic compounds. Oxidation states in organic molecules apply per carbon atom shown — molecules with multiple carbons may have different states on each carbon.

Compound	Formula	C State	How to derive it
Diamond / Graphite	C	0	Elemental carbon by convention.
Methane	CH₄	−4	C + 4(+1) = 0 → C = −4
Ethane	C₂H₆	−3	Per carbon: C − C bond = 0, 3 C−H → C = −3
Ethylene	C₂H₄	−2	Per carbon: C=C contributes 0, 2 H (+1 each) → C = −2
Acetylene	C₂H₂	−1	Per carbon: C≡C = 0, 1 H → C + 1 = 0 → C = −1
Methanol	CH₃OH	−2	C + 3(+1) + (−2) + (1) = 0 → C = −2
Formaldehyde	HCHO	0	C + (−2) + 2(+1) = 0 → C = 0
Formic Acid	HCOOH	+2	C + 2(−2) + 2(+1) = 0 → C = +2
Acetic Acid (COOH)	CH₃COOH (carboxyl C)	+3	COOH: C + 2(−2) + (+1) = 0 → C = +3
Carbon Monoxide	CO	+2	C + (−2) = 0 → C = +2
Carbon Dioxide	CO₂	+4	C + 2(−2) = 0 → C = +4
Carbonic Acid	H₂CO₃	+4	C + 3(−2) + 2(+1) = 0 → C = +4
Calcium Carbonate	CaCO₃	+4	CO₃²⁻: C + 3(−2) = −2 → C = +4
Tetrachloromethane	CCl₄	+4	Cl is −1; C + 4(−1) = 0 → C = +4
Chloroform	CHCl₃	+2	C + 3(−1) + (+1) = 0 → C = +2
Methylene Chloride	CH₂Cl₂	0	C + 2(−1) + 2(+1) = 0 → C = 0
Chloromethane	CH₃Cl	−2	C + 3(+1) + (−1) = 0 → C = −2
Aluminum Carbide	Al₄C₃	−4	Al is +3; (4×3 + 3×C = 0) → C = −4
Calcium Carbide	CaC₂	−1	Ca is +2; (2 + 2C = 0) → C = −1
Carbon Disulfide	CS₂	+4	S is −2 (same rule as O); C + 2(−2) = 0 → C = +4

Ground State Configuration

Core (noble gas He)

Valence electrons

Two valence electrons; 4 empty slots

Notation

Full: 1s² 2s² 2p²

Noble gas: [He] 2s² 2p²

C⁴⁺ (formal): 1s² (= He core) — only via covalent bonding

C⁴⁻ (formal): 1s² 2s² 2p⁶ (= Ne core) — only via covalent bonding

Ionization Steps

[He] 2s² 2p²

Neutral atom (6 electrons)

C⁺

[He] 2s² 2p¹

Remove 2p electron — IE₁ 1086.5 kJ/mol

C²⁺

[He] 2s²

Remove 2nd 2p electron — IE₂ 2352.6 kJ/mol

C³⁺

[He] 2s¹

Remove 2s electron — IE₃ 4620.5 kJ/mol

C⁴⁺

[He]

Remove last 2s electron — IE₄ 6222.7 kJ/mol — only through covalent bonds in practice

Why carbon is unique among elements
Carbon's four valence electrons sit exactly halfway through the 2p subshell. This means carbon can form four equivalent covalent bonds (sp³ hybridization in methane), three bonds with a double bond (sp², as in ethylene), or two bonds with a triple bond (sp, as in acetylene). No other element combines such bond flexibility with the ability to catenate (bond to itself) across millions of stable chain and ring structures.

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Summary

Reference tool covering all carbon oxidation states from −4 to +4, with compound examples, electron configuration, and an interactive oxidation state identifier.

How it works

Select a tab — Oxidation States, Compounds, Electron Config, or Identifier — to explore each topic.
The atom card at the top shows carbon's core atomic data: number, mass, group, and electronegativity.
The Oxidation States tab lists every state from −4 to +4 with stability notes and representative examples.
The Compounds tab shows a searchable table of common carbon-containing molecules and their C oxidation state.
The Electron Config tab walks through orbital filling, ionization steps, and Lewis-acid/base behavior.
The Identifier tab lets you pick a molecule from a list and see its carbon oxidation state explained step by step.

Use cases

Students learning oxidation state rules for organic and inorganic chemistry.
Chemistry teachers preparing lesson plans on carbon's unique redox versatility.
Anyone studying for A-level, AP Chemistry, or university general chemistry exams.
Researchers needing a quick reference for carbon redox states in reaction mechanisms.
Engineers working with carbon materials, carbides, or carbon capture chemistry.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu