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Argon

Element 18 · Noble gas

Specimen

Atomic number
18
Atomic mass
39.95
State at room temperature
Gas
Melting point
-189.3 °C
Boiling point
-185.8 °C
Density
0.001784 g/cm³
Discovered
1894

Atomic mass from IUPAC.1 Other physical data from PubChem.2

Can I eat it?

In food and water
Allowed in food. The EU allows argon gas as food additive E 938, with no fixed maximum amount (quantum satis). 3

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The atom

Ar
ShellElectrons
1 (K) 2
2 (L) 8
3 (M) outermost 8
Total18

Configuration [Ne] 3s² 3p⁶

3s ↑ ↓
3p ↑ ↓ ↑ ↓ ↑ ↓
A shell diagram: each ring is an electron shell and each dot is one electron. The nucleus holds 18 protons. The outermost shell is shown in red. Electrons do not travel on rings: they fill orbitals, regions where an electron is likely to be found. The boxes are those orbitals for the electrons outside the Ne core, with one arrow per electron.

Related elements

Group 18
He Helium Ne Neon Kr Krypton Xe Xenon Rn Radon Og Oganesson

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Sources

  1. 1

    IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2024. Abridged Standard Atomic Weights 2024 .

    The atomic mass shown for the 84 elements that have a standard atomic weight.

  2. 2

    National Center for Biotechnology Information (PubChem), 2026. Periodic Table of Elements .

    Electron configuration, melting and boiling points, density and discovery year for all 118 elements.

  3. 3

    European Commission, 2011. Commission Regulation (EU) No 1129/2011 establishing a Union list of food additives , Annex, Parts B and E.

    The text as adopted by the EU in 2011, from legislation.gov.uk. Later EU amendments are not in it.

    • E 938 Argon quantum satis
  4. 4

    National Institute of Standards and Technology (NIST), 2026. Atomic Weights and Isotopic Compositions for All Elements .

    Isotopic composition of each element; the most abundant isotope sets the neutron count in the nucleus view.