Element 18
Argon (Ar)
Argon (Ar) is element 18 of the periodic table, a noble gas in period 3, group 18 (p-block) with an atomic mass of 39.948 and is a gas at standard conditions.
At a glance
- Atomic number
- 18
- Symbol
- Ar
- Atomic mass
- 39.948 u
- Category
- Noble gases
- Period
- 3
- Group
- 18
- Block
- p-block
- Phase at STP
- gas
Electron structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6
- Shorthand configuration
- [Ne] 3s2 3p6
- Electrons per shell
- 2, 8, 8
- Oxidation states
- 0
Physical properties
- Melting point
- 83.8 K
- Boiling point
- 87.3 K
- Density
- 0.0017837 g/cm3
- Phase
- gas
Atomic properties
- Atomic radius
- 71 pm
- Covalent radius
- 106 pm
- Van der Waals radius
- 188 pm
- First ionization energy
- 1521 kJ/mol
- Electron affinity
- 0 kJ/mol
Notable isotopes
| Isotope | Mass | Abundance | Stability |
|---|---|---|---|
| Ar-40 | 39.96238 | 99.6% | Stable |
Common uses
- Welding
- Light bulbs
- Preserving wine
- Thermal insulation
Discovery
- Year
- 1894
- Discovered by
- Lord Rayleigh, William Ramsay
- Country
- England