Roentgenium is a synthetic, highly radioactive transactinide in group 11. Only a few atoms have been made. Its most stable confirmed isotope (Rg-282) lasts about 2 minutes. Properties are largely predicted.
Roentgenium (Rg) is a synthetic transactinide with atomic number 111. It lies in Group 11 (the coinage-metal family with Cu, Ag, Au) and in period 7. It does not occur in nature and must be made atom-by-atom in particle accelerators.
Rg isotopes are created in fusion–evaporation reactions by firing medium-mass ions at heavy targets. A classic discovery route is:
\(^{209}\mathrm{Bi}(^{64}\mathrm{Ni},\,n)\,^{272}\mathrm{Rg}\)
The compound nucleus cools by evaporating neutrons \((n)\) and the newborn Rg atoms are swept rapidly to detectors.
Fresh Rg atoms recoil from the target into a separator and are implanted in position-sensitive detectors. Identification relies on time-correlated decay chains with characteristic energies and lifetimes, typically \(\alpha\) decay and sometimes spontaneous fission:
\(^{A}_{111}\mathrm{Rg} \;\xrightarrow{\alpha}\; ^{A-4}_{109}\mathrm{Mt} + \alpha \;\to\; \cdots\)
Several short-lived isotopes around mass numbers \(\sim 272\text{–}284\) are known. A relatively long-lived one is \(^{282}\mathrm{Rg}\) with a lifetime on the order of about 2 minutes (decays by \(\alpha\) emission). Most others live for milliseconds to seconds.
By analogy with gold (Au), Rg is expected to favor +1 in condensed-phase chemistry, with possible access to +3 in strongly oxidizing environments. Direct aqueous chemistry has not been established; insights come from single-atom gas-phase studies and relativistic quantum calculations.
Calculations suggest a ground state close to [Rn] 5f14 6d9 7s2 or a near-degenerate 6d10 7s1 (gold-like). Strong relativistic effects in the 6d/7s shells make both arrangements competitive and influence Rg’s expected “noble-metal” behavior.
By periodic analogy, halides and oxohalides could be accessible in gas-phase, single-atom experiments (e.g., RgCl, RgF or oxychloride fragments). However, definitive series remain a research topic due to extreme scarcity and short half-lives.
Experiments produce only a few atoms of Rg at a time, and they decay quickly. That makes it impossible to prepare macroscopic samples to measure density, melting point, crystal structure, or color. Most property estimates are therefore predictions from theory and trends.
Yes. Rg is a radiotoxic heavy element. Although handled in atom-scale amounts, research requires remote manipulation, high-vacuum separators, shielding, HEPA-filtered ventilation, dosimetry, and compliant radioactive-waste procedures in specialized facilities.
Production (stylized):
\(^{209}\mathrm{Bi}(^{64}\mathrm{Ni},\,n)\,^{272}\mathrm{Rg}\)
Generic decay step:
\(^{282}\mathrm{Rg} \;\xrightarrow{\alpha}\; ^{278}\mathrm{Mt} + \alpha\)