Roentgenium (Rg)

Wilhelm Conrad Röntgen found X-rays in Würzburg in November 1895, published within weeks, and then did something unusual with the most commercially valuable discovery in the history of physics: he refused to patent it. He held that the results of scientific research belonged to humanity, took no royalties from the radiography industry that grew up almost overnight, and donated the money from the first Nobel Prize in Physics, awarded to him in 1901, to the University of Würzburg. He died in 1923 with his savings destroyed by German hyperinflation.

Element 111 carries his name, spelled roentgenium rather than röntgenium. IUPAC element names do not use diacritics, so the umlaut is transliterated in the standard German way, and the symbol Rg carries no trace of it either.

Three atoms in December 1994

The element was produced at the heavy-ion laboratory outside Darmstadt on 8 December 1994, about a month after element 110, by the same group using the same approach with a bismuth target and a nickel-64 beam. Three atoms of roentgenium-272 were identified through their alpha decay chains.

Three atoms is not many, and the discovery was not immediately accepted. The joint IUPAC and IUPAP working party reviewed it in 2001 and concluded the evidence was insufficient — not that it was wrong, but that a claim resting on three chains needed corroboration. Confirmation came from repeat experiments at Darmstadt in 2000 and from an independent RIKEN campaign in Japan in 2003, and the element was formally recognised in 2003. The name was approved in November 2004.

The sequence is a useful illustration of how this field actually adjudicates. A claim is not rejected or accepted on its first appearance; it sits in a queue until somebody else's apparatus reproduces it.

Under gold, and predicted not to behave like it

No chemistry has been done on roentgenium. Everything that follows is calculation, and the calculations are interesting precisely because they predict element 111 will not be a heavier gold.

Group 11 runs copper, silver, gold, roentgenium. Going down that group, the most stable oxidation state has been drifting: copper favours +2, silver strongly favours +1, and gold is famous for being awkward, with +3 as common as +1 and a well-known ability to form the auride ion Au⁻, in which gold behaves almost like a halogen.

Relativistic calculations predict roentgenium will push all of this further. The 6d orbitals are expected to be destabilised relative to the 7s, so the +3 state should be the most stable one and +5 should be reachable, while the +1 state that dominates silver chemistry should be difficult. Roentgenium is also predicted to have an electron affinity higher than gold's, which would make the Rg⁻ anion more stable than the auride, and to be a very dense solid.

Every one of those statements is the output of a computer model. None has been tested, and there is no immediate prospect of testing them: the longest-lived isotope, roentgenium-282, survives on the order of a minute or two, and it is produced only as a step in the decay chain of element 115 rather than directly. Chemistry on element 111 would require both a longer-lived isotope and a production rate that does not currently exist.

Naming a discovery rather than a discoverer's institution

Most of the elements in this stretch of the periodic table are named for the places that made them — a German state, a German city, a Russian town, a Californian laboratory. Element 111 breaks the pattern by honouring a person from outside the field entirely, whose work predates nuclear physics as a discipline.

The connection the discoverers drew was between X-rays and the detection methods their own work depends on. Röntgen's photographic plates were the first instrument that let anyone see inside matter without opening it, and the descendants of that idea — silicon detectors reading out the energy of individual particles — are what makes it possible to claim an element on the evidence of three atoms. The name places an 1895 discovery at the root of a 1994 one.