18 Ar Argon 39.95
Noble gas
Argon 氩
[Ne] 3s² 3p⁶
- Period 3
- Group 18
- Block p
- Gas
Electron configuration
1s² 2s² 2p⁶ 3s² 3p⁶
Orbital diagram (valence)
3s ↑↓
3p ↑↓↑↓↑↓
- Electrons per shell
- 2, 8, 8
- Unpaired electrons
- 0
- Zeff (Slater)
- 6.75
Properties
- Atomic weight
- 39.95
- Electronegativity (Pauling)
- no data
- First ionization energy
- 1521 kJ/mol
- Electron affinity
- no data
- Covalent radius
- 106 pm
- van der Waals radius
- 188 pm
- Melting point
- 83.8 K
- Boiling point
- 87.3 K
- Density
- 0.001784 g/cm³
- Melting / boiling point
- −189.3 °C / −185.8 °C
- Common oxidation states
- 0
- Discovered
- 1894
Natural isotopes
| Mass number A | Abundance |
|---|---|
| 36Ar | 0.3336 % |
| 38Ar | 0.0629 % |
| 40Ar | 99.60 % |
Isotope masses: AME2020; abundances: IUPAC/CIAAW representative values.
Successive ionization energies
The big jumps appear where core electrons start to be removed. Ionization energies from the NIST Atomic Spectra Database.
Argon in the course
The lessons that discuss this element most (ranked by mentions).
Periodic trend
Group 18
Data: PubChem periodic table (public domain); atomic weights are IUPAC abridged standard values; covalent radii from Cordero et al. (2008).