Recognised as Chemical element
Argon
- Ar
- Z = 18
- noble gas
Argon (Ar) is element 18, a noble gas in period 3 and group 18. Its standard atomic weight is 39.95 Da. Weights follow IUPAC standard atomic weights, 2021 revision.
Identity
SymbolAr
Standard atomic weight39.95atomic mass units (Da)
Mass in kilograms6.6338536 × 10^-26
Categorynoble gas
Group18
Period3
Blockp-block
Electrons in a neutral atom18
Neutrons in the most common isotope22≈
Electron configuration
Configuration1s² 2s² 2p⁶ 3s² 3p⁶ground state, subshells written in order of n
Noble gas shorthand[Ne] 3s² 3p⁶
Electrons per shell2, 8, 8K, L, M and outward
Electrons in the outer shell8
Unpaired electrons0Hund's rule; none unpaired, so the free atom is diamagnetic
Madelung ruleFollowedthe ground state is what the n + l filling order predicts
Quantities
Molar mass39.95 g/mol
Mass of one mole39.95 grams
Atoms in one gram1.5074195 × 10^22
Mass of one atom6.6338536 × 10^-23 g
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