Roentgenium (Rg)
Isotopes of Roentgenium
| Isotope | Atomic Mass | Half-life | Mode of Decay |
| Rg-272 | 272.1535 | 0.0015 seconds | α to Mt-268 |
| Rg-279 | 279 | 0.17 seconds | α to Mt-275 |
| Rg-280 | 280 | 3.60 seconds | α to Mt-276 |
Roentgenium was first synthesized in 1994 at the Gesellschaft für Schwerionenforschung (Institute for Heavy Ion Research — GSI) in Darmstadt, Germany, by an international team led by Sigurd Hofmann. Chemically, roentgenium should be in the same group as the elements copper, silver, and gold. Its name honors German physicist Wilhelm Conrad Röntgen (also spelled Roentgen), the discoverer of x-rays.
Roentgenium is calculated to have similar properties to its lighter homologues — copper, silver and gold — although it may show some differences as well. It is predicted to be a noble metal, and it is expected to be a solid under normal conditions and to crystallize in the body-centered cubic structure. All of its isotopes are extremely unstable and radioactive; in general, the heavier isotopes are more stable than the lighter.
Properties of Roentgenium
| Name | Roentgenium |
| Symbol | Rg |
| Atomic number | 111 |
| Atomic weight | [280] |
| Standard state | Presumably a solid at 298 °K |
| CAS Registry ID | 54386-24-2 |
| Group in periodic table | 11 |
| Group name | None |
| Period in periodic table | 7 |
| Block in periodic table | d-block |
| Color | Unknown, but probably metallic and silvery white or grey in appearance |
| Melting point | No data available |
| Boiling point | No data available |
| Density of solid | 28.7 g/cm3 (predicted) |
| Electron configuration | [Rn]5f146d97s2 |
