- Roentgenium (Rg) is a synthetic, highly radioactive element with atomic number 111, located in Group 11 of the periodic table, directly beneath gold. It is part of the transactinide series and the 6d transition metals.
- Its predicted electron configuration is [Rn] 5f¹⁴ 6d⁹ 7s², paralleling copper, silver, and gold. Roentgenium is expected to exhibit a +1 oxidation state most commonly, like other Group 11 elements, though higher oxidation states such as +3 and possibly +5 could exist under special conditions. Its atomic structure contains one hundred and eleven protons, around one hundred and seventy to one hundred and seventy-five neutrons depending on the isotope, and one hundred and eleven electrons in seven shells.
- The most stable known isotope is roentgenium-282 (²⁸²Rg), with a half-life of about 2.1 minutes, significantly longer than most neighboring superheavy isotopes.
- Roentgenium was first synthesized on December 8, 1994, at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany, by a team led by Peter Armbruster and Gottfried Münzenberg. The discovery was achieved by bombarding a bismuth-209 (²⁰⁹Bi) target with accelerated nickel-64 (⁶⁴Ni) ions, producing a single atom of roentgenium-272 (²⁷²Rg). This marked the beginning of experimental confirmation of element 111, though further isotopes were later produced to solidify its discovery.
- The element was named roentgenium in honor of Wilhelm Conrad Röntgen, the German physicist who discovered X-rays in 1895, a groundbreaking contribution to both science and medicine. The name and symbol Rg were officially approved by IUPAC in 2004, making it one of the more recently named superheavy elements.
- Roentgenium has no known practical applications due to its instability and the fact that it is produced atom by atom. Its main importance lies in research, particularly in testing theoretical models of superheavy elements and extending the periodic table’s chemical behavior.
- Chemically, roentgenium is predicted to behave similarly to gold, likely forming compounds such as roentgenium(I) chloride (RgCl) and roentgenium(I) hydroxide (RgOH). However, relativistic effects may alter its properties, potentially making it more chemically inert than gold. No direct chemical experiments have been carried out due to the small number of atoms produced.
- Biologically, roentgenium has no natural role and is considered radiotoxic, though it decays too quickly and exists in such tiny amounts that it poses no biological risk outside nuclear laboratories.
- Environmentally, roentgenium does not occur in nature. It is created only under controlled laboratory conditions in particle accelerators and decays rapidly into lighter elements, leaving no environmental trace.
