Roentgenium is a radioactive element with symbol Rg and atomic number 111. It is a transition metal that is predicted to be a solid at room temperature. Roentgenium is a synthetic element that is not found in nature.
Sigurd Hofmann, Peter Armbruster, Gottfried Münzenberg, and their team discovered the element on December 8, 1994 at the Institute for Heavy Ion Research (Gesellschaft für Schwerionenforschung or GSI) in Darmstadt, Germany. They bombarded a bismuth-209 target with nickel-64 nuclei, obtaining three nuclei of roentgenium-272:
20983Bi + 6428Ni → 272111Rg + 10n
However, the Joint Institute for Nuclear Research in Dubna (then in the Soviet Union) had previously performed this reaction in 1986. The 2001 IUPAC/IUPAP Joint Working Party (JWP) concluded there was insufficient evidence from the Russian experiment to award discovery to that team.
The GSI repeated its experiment in 2002 and found another three atoms of roentgenium, leading the JWP to acknowledge their element discovery.
Under Mendeleev’s naming convention, element 111 was eka-gold prior to its discovery. The IUPAC called it unununium (Uuu), which is the placeholder name corresponding to the atomic number. Since basically no one could consistently spell or pronounce the IUPAC name, it went by the name “111” until the GSI proposed the name of roentgenium and element symbol Rg. The name honors German physicist Wilhelm Conrad Röntgen (spelled Roentgen in English), who discovered x-rays. The IUPAC formally accepted the name and symbol on November 1, 2004.
Appearance and Properties
Researchers predict roentgenium is a solid transition metal at room temperature. Its color is unknown, but may be coppery or golden, like its homologs above it on the periodic table.
Like silver and gold, roentgenium likely is a noble metal. While noble metals participate in chemical reactions, they resist corrosion.
The predicted oxidation states of roentgenium are +3 and +5, likely with a less stable +1 state. Scientists expect roentgenium(III) has about the same reactivity as gold(III).
The predicted electron configuration is [Rn] 5f14 6d9 7s2. Breaking it down, the electrons per shell are 2, 8, 18, 32, 32, 17, 2.
Although its lighter homologs crystallize in the body-centered cubic structure, roentgenium has different electron charge densities and probably crystallizes as a face-centered cubic (fcc).
Researchers predict roentgenium is extremely heavy, with a density around 22-24 g/cm3. If so, this makes roentgenium the heaviest element on the periodic table, since the densest measured element is osmium at 22.61 g/cm3.
Roentgenium Isotopes and Abundance
Roentgenium is a radioactive element. It has no stable natural isotopes. So far, nine isotopes are reported, with masses of 272, 274, 278-283, and 286. These isotopes decay via alpha decay or spontaneous fission. Roentgenium-280 may also use electron capture.
The heavier isotopes tend to be more stable than the lighter ones. The most stable isotope is roentgenium-282, which has a half-life of 100 seconds. However, roentgenium-286 has an unconfirmed half-life of 10.7 minutes. If this report is substantiated, Rg-286 is among the longest-lived superheavy isotopes.
Only a few atoms of roentgenium have been produced and all of the isotopes have a short half-life, so there are no practical uses of the element. Right now, its only application is for research purposes. Mainly this involves further studies on the chemistry of isotope Rg-282, which has a half-life of 100 seconds.
Biological Role and Toxicity
Because it does not occur naturally, roentgenium serves no function in any biological organism. Because it is a noble metal, it likely is not particularly toxic. However, it’s extreme radioactivity poses a health risk.
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. Amsterdam. ISBN 978-0-08-037941-8.
- Fricke, Burkhard (1975). “Superheavy elements: a prediction of their chemical and physical properties”. Recent Impact of Physics on Inorganic Chemistry. Structure and Bonding. 21: 89–144. doi:10.1007/BFb0116498
- Hofmann, S.; Ninov, V.; Heßberger, F.P.; Armbruster, P.; Folger, H.; Münzenberg, G.; Schött, H. J.; Popeko, A. G.; Yeremin, A. V.; Andreyev, A. N.; Saro, S.; Janik, R.; Leino, M. (1995). “The new element 111”. Zeitschrift für Physik A. 350 (4): 281–282. doi:10.1007/BF01291182
- Östlin, A.; Vitos, L. (2011). “First-principles calculation of the structural stability of 6d transition metals”. Physical Review B. 84 (11): 113104. doi:10.1103/PhysRevB.84.113104
- Weast, Robert (1984). Handbook of Chemistry and Physics. Chemical Rubber Company Publishing. Boca Raton (FL). ISBN 0-8493-0464-4.