Argon is the chemical element with atomic number 18 and is a noble gas used in some lighting.
Its symbol is Ar, and it makes up about 0.934% of Earth’s atmosphere by volume. Argon is colorless, odorless, and chemically very unreactive because its outer electron shell is complete.
Argon was discovered in 1894 by Lord Rayleigh and William Ramsay after they noticed that nitrogen extracted from air was slightly denser than nitrogen made from chemical compounds. The name comes from the Greek word argos, meaning “idle” or “inactive.”
Argon is used inside incandescent and fluorescent lamps, where it helps protect hot filaments and electrodes. It is also used as a shielding gas in arc welding. Argon is sometimes confused with neon because both are used in lighting, but they are different elements with different atomic numbers and emission colors.