Argon
noble gasProperties
| Property | Value |
|---|---|
| Atomic Mass | 39.948 amu |
| Category | noble gas |
| Group | 18 |
| Period | 3 |
| Electron Configuration | 1s2 2s2 2p6 3s2 3p6 |
| Oxidation States | 0 |
| Melting Point | 83.81 K (-189.3 °C) |
| Boiling Point | 87.302 K (-185.8 °C) |
| Density | 0.001784 g/cm³ |
| Discovered By | Lord Rayleigh (1894) |
About Argon
Argon was the noble gas that broke the periodic table open, and Rayleigh and Ramsay caught it through a discrepancy of less than 0.5 percent in the density of nitrogen. Atmospheric N2 came in heavier than N2 stripped from ammonia, and that gap turned out to be roughly 1 percent of an unreactive monatomic gas the table had no slot for. Ramsay had to insert a whole new column. The Ar-40 isotope that dominates the modern atmosphere isn't primordial — it accumulated over geological time from K-40 electron capture in the crust and mantle, which is what gives K-Ar and Ar-Ar geochronology their reach back to the Hadean. In a working lab argon is the gas you reach for when nitrogen would react: TIG welds on titanium and stainless, Schlenk-line air-free synthesis of organolithiums or Grignards, glovebox atmospheres for lithium-air battery research, sputter targets in semiconductor fabs. Industrially it falls out of cryogenic air separation as the highest-boiling-point fraction after oxygen, which is why it's cheap enough to flood a 10-cubic-meter glovebox without thinking twice.
Fun Fact
Roughly 99 percent of the argon in Earth's atmosphere is Ar-40 produced by potassium-40 decaying in the crust over the past 4.5 billion years — the planet has been slowly outgassing its own clock.
Common Uses
- Schlenk-line and glovebox inert atmosphere for air-sensitive synthesis
- TIG and MIG shielding gas for titanium, stainless, and aluminum welding
- Sputter gas for thin-film deposition in semiconductor and optics fabs
- K-Ar and Ar-Ar radiometric dating of volcanic rocks and meteorites
- Excimer laser fill (ArF at 193 nm) for photolithography stepper tools