ElementsWhat is argon?
Argon is a gas without colour or smell that makes up nearly 1 percent of the air. It is the cheapest gas that does not react with hot metals.
What is argon used for?
Shielding gas for welding, filling light bulbs, the gap in double-glazed windows, and protecting old documents.
Where the name comes from
From the Greek word argos, meaning lazy or inactive, because it does not react.
Key facts
- Symbol
- Ar
- Atomic number
- 18
- Atomic mass
- 39.9 u
- Family
- Noble gas
- Period
- 3
- Group
- 18
- Block
- p
- State at room temperature
- Gas
- Melting point
- -189.3 °C (83.8 K, -309 °F)
- Boiling point
- -185.8 °C (87.3 K, -303 °F)
- Density
- 0.0017837 g/cm³ (as a gas at 0 °C)
- Electrons per shell
- 2, 8, 8
- Electron configuration
- [Ne]3s2 3p6
- Common oxidation states
- 0
- Electronegativity (Pauling)
- no value
- First ionisation energy
- 15.76 eV
- Electron affinity
- no value
- Atomic radius (van der Waals)
- 188 pm
- Discovered
- 1894
Place in the periodic table
Argon is element number 18. It sits in period 3 (row 3) of the periodic table, in group 18 (column 18), and belongs to the p-block. Just before it comes chlorine (17), and just after it comes potassium (19). In the same column, neon is above it and krypton is below it. Elements in one column tend to behave alike.
Family: Noble gases.
Physical properties
At room temperature argon is a gas. It melts at -189.3 °C and boils at -185.8 °C, so it stays liquid over a range of 4 degrees. One litre of the gas weighs about 1.784 grams at 0 °C and normal pressure. That is heavier than air, which weighs about 1.29 grams a litre. It has the 7th lowest melting point of all elements.
Inside the atom
An atom of argon has 18 protons in its nucleus and, when neutral, 18 electrons around it. The electrons are arranged in 3 shells: 2, 8, 8. The outermost shell holds 8 electrons. Written in full, the electron configuration is [Ne]3s2 3p6.
Removing one electron from an atom takes 15.76 electronvolts (about 1,521 kilojoules per mole). One mole of argon weighs 39.9 grams, so a single gram contains about 1.51 × 1022 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains argon with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.