Argon Oxidation States

Argon (Ar) has one common oxidation state: 0. Its complete 3s² 3p⁶ valence shell makes it essentially inert, though one argon compound (HArF) has been confirmed at extremely low temperatures.

18 Ar 39.948

Argon

Noble Gas — Period 3, Group 18

Symbol: Ar
Atomic no.: 18
Atomic mass: 39.948 u
Block: p-block
Phase: Gas
Discovered: 1894

Electron Configuration

1s
e
e
Core — complete
2s
e
e
Core — complete
2p
e
e
e
e
e
e
Core — complete (forms [Ne] core)
3s
e
e
Valence — filled
3p
e
e
e
e
e
e
Valence — filled (octet complete)
Notation
Full: 1s2 2s2 2p6 3s2 3p6
Noble gas: [Ne] 3s2 3p6

All 18 electrons fill the first three principal shells completely. The filled 3p subshell closes argon's valence shell, leaving no low-energy empty orbitals available for bonding.

Key Properties

Ionization energy (1st) 15.759 eV
Ionization energy (2nd) 27.630 eV
Electronegativity None (Pauling)
Boiling point −185.85 °C (87.30 K)
Melting point −189.35 °C (83.80 K)
Density 1.784 g/L (STP)
Known compounds HArF (at 7.5 K only)

Oxidation States of Argon

Click a row to see details.

State Occurrence Example
0 Always (standard conditions) Ar (elemental gas)
0* Rare — cryogenic matrix only HArF (7.5 K)

Noble Gas Oxidation State Comparison

Heavier noble gases (Kr, Xe) achieve positive oxidation states with fluorine and oxygen. Argon sits at the boundary — one cryogenic compound exists, but no room-temperature chemistry.

Why Argon Is Essentially Inert

    The One Argon Compound: HArF

    Name
    Argon Fluorohydride
    Formula
    HArF
    Ar Oxidation State
    0 (debated; formally 0 in IUPAC)
    Conditions
    Synthesized in 2000 by Räsänen et al. at the University of Helsinki by UV photolysis of HF in solid argon at 7.5 K. Decomposes above ~17 K. Ar is formally in the 0 oxidation state even in this molecule — the bonding is better described as a charge-transfer complex than a true covalent compound with an ionic argon center.

    Summary

    Argon (Ar) has one common oxidation state: 0. Its complete 3s² 3p⁶ valence shell makes it essentially inert, though one argon compound (HArF) has been confirmed at extremely low temperatures.

    How it works

    1. Use the left panel to review argon's element data and click "Copy Element Data" to copy a plain-text reference card.
    2. The electron configuration panel shows the filled 3s and 3p orbitals that produce argon's chemical inertness.
    3. The oxidation states table lists every known state with its stability; click a row for a detailed explanation.
    4. The noble gas comparison chart places argon alongside all six Group 18 elements to show how reactivity increases down the group.
    5. The inertness explainer lists the four chemical reasons argon almost never reacts.
    6. Key properties are listed for quick reference — ionization energies, boiling point, density, and known compounds.

    Use cases

    • Looking up argon's oxidation state for chemistry homework or an exam.
    • Teaching why noble gases have oxidation state 0 using a familiar, abundant element.
    • Comparing argon to heavier noble gases like krypton and xenon that do form compounds.
    • Understanding why argon is used as an inert shielding gas in welding and semiconductor manufacturing.
    • Studying period 3 elements and the effect of a complete octet on reactivity.
    • Background reading before working with noble gas chemistry or excimer lasers.

    Frequently Asked Questions

    Last updated: 2026-07-08 · Reviewed by Nham Vu