Elementymology & Elements Multidict

memory peg	Heavy radioactive gas melting point -71 °C; -96 °F boiling point -62 °C; -79 °F density 0.0097 g/cc; 0.61 pounds/cubic foot
1899 Pierre & Marie Curie, France
radium = element #88

In 1899, Robert B. Owens (1870-), professor of electrical engineering at McGill University in Montreal, was trying to measure radiation from Thorium. Every time he made a measurement, he got a different result. Together with Ernest Rutherford (1871-1937), also teaching at McGill University, he studied this phenomenon and they observed that

"the radiation from thorium oxide was not constant, but varied in a most capricious manner." whereas "all the compounds of Uranium give out a radiation which is remarkably constant" (note).

In the same year Pierre and Marie Curie observed a similar phenomenon with Radium, except that the "gas" emitted by Radium remained radioactive for a month (note). In 1900, Friedrich Ernst Dorn (1848-1916) confirmed the findings of Rutherford and the Curies (note), thus Radium Emanation (Ra Em). Most standard sources on the chemical elements list Dorn as the discoverer in 1900. In fact he had merely repeated the Curies’ experiment with more active Radium compounds.

In fact that the emanations emitted by Radium are a radioactive gas was clearly demonstrated by Rutherford and Brooks in 1901, though they were careful to give credit to the prior observations of the Curies (note).

In 1903, Fritz Giesel observed emanations from Emanium (note) and in the same year André-Louis Debierne (1874-1949) from Actinium (note). In 1906, when was concluded that Giesel's Emanium was identical with Debierne's Actinium, both emanations were therefore called Actinium Emanation (Ac Em).

The likeness of the spectra of these three gases with those of Argon, Krypton and Xenon, and its chemical inertia suggested that the "emanations" could contain a new element from the noble gases family. Several names were suggested:

	Radium Emanation	Thorium Emanation	Actinium Emanation
Ramsay & Collie, 1904	Exradio	Exthorio	Exactinio
Perrin, 1919	Radeon	Thoreon	Actineon
Schmidt, 1918	Radon	Thoron	Akton
Adams, 1920	Radon	Thoron	Actinon

"It may be remembered that, at the Chemical Congress held in Paris in 1900, it was suggested that no element should receive a name until its spectrum had been mapped. (...) The «emanation from radium», however, is a cumbrous expression, and sufficient evidence has now been accumulated that it is an element, accepting that word in the usual sense. It is true that it is only a transient element, and ought in justice to be called a compound; but of what? It stands on a wholly different plane to any known compound (...) It is a gas; it follows Boyle's law; (...) it resembles the gases of the argon series in its indifference to chemical reagents (...) Now, it appears advisable to devise a name which should recall its source, and, at the same time, by its termination, express the radical difference which undoubtedly exists between it and other elements. As it is derived from radium, why not name it simply «exradio»? Should it be found that the emanation, which is supposed to be evolved from thorium, is really due to that element, and not to some other element mixed with thorium in exceedingly small amount, a similar name could be given, namely «exthorio». If the existence of actinium as a definite element is established, its emanation would appropriately be named «exactinio»." (note)

In 1923, the International Committee for Chemical Elements and the Union internationale de la chimie pure et appliquée chose for the names proposed by Schmidt and Adams: Radon, Thoron, and Actinon, with symbols Rn, Tn, and An.

Later, when isotopes were numbered instead of named, the name of the element became Radon.

• McGill Rutherford Museum, Emanations from Thorium and Radium (on line).
• Edelgase. Gmelins Handbuch der anorganische Chemie, 8. Aufl.; System-Nummer 1 (1926).
• David J. Brenner, Rutherford, the Curies, and Radon (PDF on line)
• Was ist Radon? (on line).