argon

Colourless, odourless, non-metallic, gaseous element, atomic number 18, relative atomic mass 39.948. It is grouped with the noble gases (rare gases) in Group 0 of the periodic table of the elements. It was long believed not to react with other substances, but observations now indicate that it can be made to combine with boron fluoride to form compounds. It constitutes almost 1% of the Earth's atmosphere, and was discovered in 1894 by British chemists John Rayleigh and William Ramsay after all oxygen and nitrogen had been removed chemically from a sample of air. It is used in electric discharge tubes and argon lasers.