Roentgenium · element 111
Named for the man who discovered X-rays, and expected to be gold's strange heavy cousin
Key facts
In December 1994, a few weeks after finding darmstadtium, the same team at GSI in Darmstadt caught three atoms of element 111. Ten years later it was named roentgenium, after Wilhelm Rontgen, the German physicist who discovered X-rays in 1895 and received the very first Nobel Prize in Physics.
Roentgenium sits directly under gold in group 11. That makes it one of the most tempting elements for theorists, because gold's colour, its softness and its resistance to tarnish are all consequences of relativity acting on its electrons. Roentgenium should show those effects even more strongly, and calculations suggest it might not behave like gold at all.
Where it is found
Roentgenium does not exist in nature. A research group claimed in 2008 to have found traces of a long-lived isotope in natural gold, but the result has never been reproduced and is not accepted. All known isotopes decay within minutes at most. Every roentgenium atom ever detected was made in an accelerator, and the grand total is probably fewer than a hundred.
The discovery experiment used cold fusion, firing nickel-64 at bismuth-209 to produce roentgenium-272, which decays in a few thousandths of a second. The longer-lived isotopes are reached indirectly. When moscovium-288 is made at Dubna from americium-243 and calcium-48, it decays through nihonium to roentgenium-280, and heavier moscovium isotopes give roentgenium-282, the most stable version known.
How it was discovered
Sigurd Hofmann's group at GSI recorded three atoms of roentgenium-272 on 8 December 1994. Each was identified by a chain of alpha decays that ended in known isotopes, but three events was a thin basis, and IUPAC asked for more. GSI repeated the experiment in 2000 and observed further atoms, and RIKEN in Japan confirmed the result independently in 2003. Credit was formally assigned to GSI in 2003.
The discoverers proposed roentgenium in 2004 and IUPAC approved it the same year with the symbol Rg. Rontgen had died in 1923. He refused to patent his discovery, believing that X-rays belonged to everyone, and donated his Nobel Prize money to his university. Choosing an honouree from the earliest days of modern physics linked a brand-new element to the roots of the science.
What we use it for
Roentgenium has no uses, and its chemistry has never been studied. Roentgenium-282 lives for a minute or two, which is long enough in principle, but it is produced only as a decay product a few atoms at a time, so the experiments have not yet been possible.
The reason theorists find it fascinating is gold. In gold, relativity pulls the 6s electron closer to the nucleus and lifts the 5d electrons, which is why gold absorbs blue light and looks yellow. In roentgenium these effects are much larger. Calculations suggest it may prefer a +3 oxidation state rather than gold's +1, may hold electrons even more tightly, and may not be gold-coloured at all. Meanwhile its isotopes serve as checkpoints in the decay chains that prove heavier elements exist.
Reading the numbers
The atomic mass of 282 is the mass number of the longest-lived isotope, not a natural average. The predicted density of about 29 grams per cubic centimetre is a calculation. Gold's is 19.3, so roentgenium is expected to be half again as dense. No melting point, boiling point, electronegativity or ionisation energy has been measured, which is why those values are absent.
The configuration shown, [Rn] 5f14 6d10 7s1, is what you get by copying gold one row up. Detailed relativistic calculations favour 6d9 7s2 instead, with one electron moved from the d shell to the s shell because the 7s orbital is so strongly stabilised. That would make roentgenium the only group 11 element without a full d shell in its ground state, and hints that it may be less noble than gold in some ways and more so in others. Until an experiment is done, both remain possible.
Safety and the environment
Roentgenium is radioactive in every isotope, with half-lives from milliseconds to a minute or two. It cannot be stockpiled, shipped or released. The fewer than a hundred atoms ever produced were made inside shielded accelerator facilities and detected through their decay. There is no roentgenium in the environment and no route for public exposure.
Did you know?
- Wilhelm Rontgen refused to patent X-rays, saying discoveries belonged to humanity, and gave his Nobel Prize money to the University of Wurzburg.
- The 1994 discovery rested on just three atoms of roentgenium-272, each lasting a few milliseconds.
- Roentgenium is predicted to be about 50 per cent denser than gold, the element directly above it.
- Detailed calculations suggest roentgenium's outer electrons are arranged as 6d9 7s2, unlike every other group 11 element.
- Rontgen took the first medical X-ray image of a human hand, his wife Anna Bertha's, in December 1895, almost exactly 99 years before the element bearing his name was made.
More in the superheavy elements
The nearest neighbours of roentgenium in the family, by atomic number.
See all 15 superheavy elements on one page, or browse all 118 elements. Also listed under the transition metals.
Frequently asked questions
Who is roentgenium named after?
Wilhelm Conrad Rontgen, the German physicist who discovered X-rays in 1895 and received the first Nobel Prize in Physics in 1901. The name was proposed by the GSI discoverers and approved by IUPAC in 2004.
Is roentgenium like gold?
It sits below gold in group 11, but calculations suggest its chemistry may differ. Relativistic effects are expected to be stronger than in gold, possibly favouring a +3 oxidation state and a different electron arrangement. No chemistry experiments have been done yet.
What is the half-life of roentgenium?
The discovery isotope, roentgenium-272, lasts a few milliseconds. The most stable known isotope, roentgenium-282, survives for roughly a minute or two before decaying.
Has roentgenium been found in nature?
No. A 2008 claim of a long-lived roentgenium isotope in natural gold was never reproduced and is not accepted by the scientific community. All roentgenium has been made in particle accelerators.
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Written by Anthony. Updated September 2026. Numerical data from Periodic-Table-JSON (CC BY-SA), cross-checked against the Roentgenium reference article. Spotted an error? Tell us.