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# Roentgenium

 111 darmstadtium ← roentgenium → ununbium Au↑Rg↓(Uhu)
General
Name, Symbol, Number roentgenium, Rg, 111
Chemical series transition metals
Group, Period, Block 11, 7, d
Appearance unknown, probably yellow or
orange metallic
Standard atomic weight 284 g·mol−1
Electron configuration perhaps [Rn] 5f14 6d10 7s1
(guess based on gold)
Electrons per shell 2, 8, 18, 32, 32, 18, 1
Phase presumably a solid
CAS registry number 54386-24-2
Selected isotopes
Main article: Isotopes of roentgenium
iso NA half-life DM DE (MeV) DP
280Rg syn 3.6 s
References

Roentgenium (pronounced /rɛntˈgɛniəm/, /rəntˈjɛniəm/, formerly Unununium /ˌjuːnəˈnʌniəm/) is a chemical element in the periodic table that has the symbol Rg and atomic number 111, making it one of the super-heavy atoms. It is a synthetic element whose longest-lived isotope has a mass of 280 and a half-life of 3.6 seconds. Due to its presence in Group 11, it is a transition metal.

## History

It was discovered by Peter Armbruster, Gottfried Münzenber, and their team working at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany on December 8, 1994. Only three atoms of it were observed (all 272Rg), by the fusion of 209Bismuth and 64Nickel in a linear accelerator (Nickel was bombarded onto the bismuth target):

$\,^{209}_{83}\mathrm{Bi} + \,^{64}_{28}\mathrm{Ni} \, \to \,^{272}_{111}\mathrm{Rg} + \; ^1_0\mathrm{n} \;$

The name roentgenium was accepted as a permanent name on November 1 2004 in honor of Wilhelm Conrad Röntgen; before this date, the element was known under the temporary IUPAC systematic element name unununium, symbol Uuu). Some research has referred to it as eka-gold.

## Isotopes

Twelve isotopes of roentgenium are known. The longest-lived of these is 280Rg, which decays through alpha decay and has a half-life of 3.6 seconds. The shortest-lived isotope is 272Rg, which decays through alpha decay and has a half life of 1.5 ms. Another known isotope, 279Rg, decays through alpha decay and has a half-life of 170 ms.