Science, Tech, Math › Science Interesting Roentgenium Element Facts Rg or Element 111 Share Flipboard Email Print vchal / Getty Images Science Chemistry Periodic Table Basics Chemical Laws Molecules Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated January 24, 2020 Roentgenium (Rg) is element 111 on the periodic table. Few atoms of this synthetic element have been produced, but it is predicted to be a dense, radioactive metallic solid at room temperature. Here is a collection of interesting Rg facts, including its history, properties, uses, and atomic data. Key Roentgenium Element Facts Wondering how to pronounce the element name? It's RENT-ghen-ee-em Roentgenium was first made by an international team of scientists working at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany, on December 8, 1994. The team, led by Sigurd Hofmann, accelerated nuclei of nickel-64 into a bismuth-209 target to produce one single atom of roentgenium-272. In 2001, the Joint Working Party of the IUPAC/IUPAP decided the evidence was not sufficient to prove the discovery of the element, so the GSI repeated the experiment and detected three atoms of element 111 in 2002. In 2003, the JWP accepted this as evidence that the element had truly been synthesized. If element 111 had been named according to the nomenclature devised by Mendeleev, its name would be eka-gold. However, in 1979 the IUPAC recommended systematic placeholder names be given to unverified elements, so until the permanent name was decided, element 111 was called unununium (Uuu). Because of their discovery, the GSI team was allowed to suggest a new name. The name they chose was roentgenium, in honor of the German scientist who discovered x-rays, physicist Wilhelm Conrad Röntgen. The IUPAC accepted the name on November 1, 2004, nearly 10 years after the first synthesis of the element. Roentgenium is expected to be a solid, noble metal at room temperature, with properties similar to those of gold. However, based on the difference between the ground state and the first excited state of the outer d-electrons, it is predicted to be silver in color. If enough element 111 is ever produced, the metal will likely be even softer than gold. Rg+ is predicted to be the softest of all the metal ions. Unlike lighter congeners which have face-centered cubic structure for their crystals, Rg is expected to form body-centered cubic crystals. This is because the electron charge density is different for roentgenium. Roentgenium Atomic Data Element Name/Symbol: Roentgenium (Rg) Atomic Number: 111 Atomic Weight:  Discovery: Gesellschaft für Schwerionenforschung, Germany (1994) Electron Configuration: [Rn] 5f14 6d9 7s2 Element Group: d-block of group 11 (Transition Metal) Element Period: period 7 Density: Roentgenium metal is predicted to have a density of 28.7 g/cm3 around room temperature. In contrast, the highest density of any element measured experimentally to date has been 22.61 g/cm3 for osmium. Oxidation States: +5, +3, +1, -1 (predicted, with the +3 state expected to be the most stable) Ionization Energies: The ionization energies are estimates. 1st: 1022.7 kJ/mol2nd: 2074.4 kJ/mol3rd: 3077.9 kJ/mol Atomic Radius: 138 pm Covalent Radius: 121 pm (estimated) Crystal Structure: body-centered cubic (predicted) Isotopes: 7 radioactive isotopes of Rg have been produced. The most stable isotope, Rg-281, has a half-life of 26 seconds. All known isotopes undergo either alpha decay or spontaneous fission. Uses of Roentgenium: The only uses of roentgenium are for scientific study, to learn more about its properties, and for the production of heavier elements. Roentgenium Sources: Like most heavy, radioactive elements, roentgenium may be produced by fusing two atomic nuclei or via decay of an even heavier element. Toxicity: Element 111 serves no known biological function. It presents a health risk because of its extreme radioactivity.