12 November 2009
Radon, element 86, was discovered in 1900 by German physicist Friedrich Ernst Dorn. The previous year the Curies had discovered that radium gave off a radioactive gas, and it was Dorn that identified this gas as an elemental decay product of radium. The name radon is originally German, from rad- for radium and -on, indicating that it is a noble gas, like argon or neon. The name was in English use by 1918. From the Journal of the Chemical Society of that year:
Radium emanation is given the name Radon, Ro, which at once indicates its origin and its relationship to the argon group.
Note that Ro is no longer used as the chemical symbol for the element. The current symbol for Radon is Rn.
Former names for the element include niton, from the Latin nitere, to shine, and emanation or radium-emanation. These names were in use into the middle of the 20th century and are occasionally found when perusing older chemical literature.
Sources:
Oxford English Dictionary, radon, 3rd Edition, June 2008