Argon
. Argon, symbol Ar, inert gaseous element that is the third most prevalent gas in the earth's atmosphere. In group 18 (or VIIIa) of the periodic table , argon is one of the noble gases . The atomic number of argon is 18. Argon was discovered in 1894 by the British scientists Sir William Ramsay and Baron John William Strutt Rayleigh . They were led to this discovery by a discrepancy between the density of supposedly pure nitrogen, prepared from air, and actually pure nitrogen, prepared from ammonium nitrate. Argon is composed of monatomic molecules and is colorless and odorless.It constitutes 0.93 percent of the atmosphere. Argon melts at -189.3° C (-308.2° F) and boils at -185.86° C (-302.55° F). The atomic weight of argon is 39.948. In recent years chemists have been able to force most of the noble gases to form compounds. Researchers at the University of Helsinki achieved this feat with argon in 2000. They created argon fluorohydride (HArF) by shining ultraviolet light on frozen