Bright Atoms, home
Periodic table / Noble gases

18Argon

Argon is a noble gase in group 18, period 3. At 25 °C it is a gas.

Ar
Shells: 2, 8, 8. A simple picture: electrons do not move in circles.
Symbol
Ar
Atomic number
18 protons in the nucleus
Standard atomic weight
39.95 ± 0.16
Electron configuration
[Ne] 3s2 3p6
Electrons in each shell
2, 8, 8
Group, period, block
18, 3, p
Family
Noble gases
State at 25 °C
gas
Electronegativity
no value
First ionisation energy
1520.6 kJ/mol (15.7596119 eV)
Where these numbers come from

Atomic weight: IUPAC CIAAW, abridged standard atomic weights 2024. Electron configuration and ionisation energy: NIST Atomic Spectra Database. Family, state and electronegativity: PubChem. See Sources. Melting points, boiling points and densities are left out for now: published values differ between sources, and we will add them once each has been checked.