argons

Argons are atoms of argon, the chemical element with symbol Ar and atomic number 18. They are colorless, odorless, nonflammable, and largely inert at room temperature; most remain monatomic.

Natural abundance and source: Argon makes up about 0.93% of Earth's atmosphere, making it the third most abundant gas after nitrogen and oxygen. It is rare in minerals but can occur in natural gas. Industrially, argon is produced by fractional distillation of liquid air.

Isotopes: The main natural isotopes are Ar-36, Ar-38, and Ar-40, with Ar-40 about 99.6% of natural argon. There are radioactive isotopes such as Ar-39 produced cosmogenically and in nuclear reactions; Ar-39 has a half-life of about 269 years and is used in groundwater dating and tracing.

Uses: Argons are used as shielding gas in arc welding, for inert atmospheres in metal fabrication and semiconductor manufacturing, in incandescent and some fluorescent lamps, and as an insulating gas in double-pane windows; used in cryogenics.

Safety: Argon is non-toxic and non-flammable, but, as an asphyxiant, it can displace oxygen in confined spaces. It is denser than air, so it can accumulate in low-lying areas.

Etymology and history: The name comes from Greek argos, meaning idle. It was identified as a distinct element in 1894 by Rayleigh and Ramsay and isolated in 1896.