Argon

Argon is a colorless, odorless noble gas with atomic number 18. It makes up about 0.93% of Earth’s atmosphere and is chemically inert under ordinary conditions.

Noble gas: A chemical element in group 18, characterized by a filled outer electron shell and low chemical reactivity. Argon belongs to this family, whose filled outer shell accounts for its usual inertness.
Atmosphere of Earth: The layer of gases surrounding Earth, held in place by gravity. Argon is the atmosphere’s third most abundant gas, after nitrogen and oxygen.
Discovery of argon: The 1894 identification of argon as a previously unknown component of Earth’s atmosphere. Careful measurements of nitrogen’s density revealed a heavier, chemically unreactive gas.
Gas metal arc welding: A welding process that uses an electric arc and a shielding gas to join metal. Argon shields molten metal from reactive gases in common arc-welding methods.
Nitrogen: A chemical element with atomic number 7 that makes up most of Earth’s atmosphere as diatomic nitrogen gas. Nitrogen is far more abundant in air, while argon is monatomic and less reactive.
Periodic table: A tabular arrangement of chemical elements ordered by atomic number and recurring chemical properties. Argon occupies group 18 and period 3 in this arrangement.
Atmospheric composition: The proportions of gases and particles present in a planet’s atmosphere. Argon’s roughly 0.93% share is a stable component of dry air.
John William Strutt, 3rd Baron Rayleigh: A British physicist whose measurements of gas densities helped establish the existence of argon. His unexplained difference between atmospheric and chemically prepared nitrogen prompted the investigation.
Argon laser: A gas laser that uses ionized argon to produce visible or ultraviolet light. Its intense blue-green output serves specialized medical and scientific uses.
Helium: A colorless noble gas with atomic number 2 and the lowest boiling point of any element. Helium is lighter and rarer in Earth’s atmosphere, though both gases are chemically unreactive.

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