Argon
Element 18 · Noble Gas
Argon is the third most abundant gas in air, and the most useless in the best way: its full outer shell makes it almost perfectly inert, so it simply takes up space. That laziness is its job. Light bulbs are filled with argon so the hot filament does not burn away; welders blanket molten metal in argon to keep oxygen out; and double-glazed windows trap it for insulation. Argon was discovered in 1894 when Lord Rayleigh noticed air was heavier than pure nitrogen — the 'extra weight' was an unknown gas hiding in plain sight at nearly 1 percent of the atmosphere.
Key facts
| Atomic number | 18 |
|---|---|
| Atomic weight | 39.95 |
| Category | Noble Gas |
| Group / Period | 18 / 3 |
| Block | p |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 |
| Common oxidation states | 0 |
| State at STP | Gas |
| Atomic radius | 71 pm |
| Density | 0.00178 g/cm³ |
| Melting point | -189.34 °C |
| Boiling point | -185.85 °C |
Occurrence
Argon is about 0.93 percent of air by volume — the third most abundant atmospheric gas. It accumulates from the slow radioactive decay of potassium-40 in rocks.
Applications
Incandescent and fluorescent bulbs
TIG welding shield gas
Double-glazed insulating windows
Preserving documents and wine
Plasma cutting
Common compounds
- No stable compounds (noble gas)
Argon's name means 'lazy' in Greek — chemists named it for its refusal to react with anything at all.
Data source: IUPAC standard atomic weights 2021