Argon (Ar)
Argon (Ar) is element 18, a noble gas. Atomic mass 39.95, configuration [Ne] 3s² 3p⁶. Properties, isotopes, oxidation states, uses and history, with an interactive 3D atom model.
Key facts
| Atomic number | 18 |
|---|---|
| Symbol | Ar |
| Standard atomic weight | [39.792,39.963] |
| Category | Noble Gas |
| Group | 18 |
| Period | 3 |
| State at room temperature | Gas |
| Electron configuration | [Ne] 3s² 3p⁶ |
| Valence electrons | 8 |
| Common ions | No common ions |
| First ionization energy | 1521 kJ/mol |
| Atomic radius | 71 pm |
| Density | 1.633 g/L |
| Melting point | -189.34°C |
| Boiling point | -185.8°C |
| Specific heat | 0.52 J/(g·°C) |
Natural isotopes
- Ar-36: Stable (0.334%)
- Ar-38: Stable (0.063%)
- Ar-40: Stable (99.60%)
Common uses
- Welding (Shielding gas)
- Incandescent light bulbs
- Double-pane windows
Where it matters
- Preservation (Museum documents stored in Ar)
- Atmospheric science
Hazards
- Asphyxiant in confined spaces
History
| Discovered | 1894 |
|---|---|
| Discovered by | Lord Rayleigh & William Ramsay |
| Name | From Greek argos (lazy/inactive) |