Roentgenium – facts and properties
- Symbol
- Rg
- Atomic number
- 111
- Atomic mass
- 282 u
- Period
- 7
- Group
- 11
- Category
- unknown, probably transition metal
- Electron configuration
- [Rn] 5f¹⁴ 6d⁹ 7s²
- Valence electrons
- 11
- State at standard conditions
- expected to be solid
- Discovered
- 1994
Roentgenium has atomic number 111 and is an artificial, strongly radioactive element. It belongs to group 11, below gold, and is named after Wilhelm Conrad Röntgen, who discovered the rays that bear his name. In atoms this heavy, relativity visibly reshapes the electron shell, so roentgenium is expected to be even nobler than gold. None of that has been measured. It is all prediction.
Position in the periodic table
Occurrence and extraction
Roentgenium is produced only in the laboratory. No known isotope is stable. As far as is known, roentgenium-282 lives longest, with a half-life of around two minutes, but the value is uncertain because only a few decays have been seen. The isotope of the discovery, roentgenium-272, decays within milliseconds.
The element was discovered in December 1994 at GSI in Darmstadt, only a few weeks after darmstadtium. Again the team around Sigurd Hofmann fired nickel-64 ions at a bismuth-209 target, once more using cold fusion. The detector recorded three atoms, and their alpha decays led through meitnerium and bohrium to known nuclei. Later experiments, among them one in Japan, confirmed the discovery.
The element is named after Wilhelm Conrad Röntgen. In November 1895 in Würzburg he found a previously unknown radiation, which he called X-rays, and in 1901 he received the first Nobel Prize in Physics. The name roentgenium was made official in 2004, more than a hundred years after the rays were found. The spelling with oe stands in for the umlaut.
Properties and reactions
Roentgenium is in period 7 and group 11, below gold, with silver and copper above. The atomic mass 282 u is the mass number of roentgenium-282. The predicted electron configuration [Rn] 5f¹⁴ 6d⁹ 7s² differs from that of gold. In gold one s electron moves into the d shell, but in roentgenium calculations keep two electrons in the 7s shell, because relativistic effects bind them especially tightly.
This is where relativistic effects come in. In heavy atoms the inner electrons move at a noticeable fraction of the speed of light, their mass increases, and the s orbitals contract and drop in energy. The d orbitals expand in return. In gold this explains the yellow colour and part of its stability, and in mercury the fact that it is a liquid. In roentgenium the effect should be more pronounced. A very unreactive metal is therefore expected, one that gives up its electrons less readily than gold.
No sample exists. According to calculations, roentgenium would be a solid metal, clearly denser than gold. The oxidation state plus three is expected above all, and some calculations allow higher ones. No chemical measurements on roentgenium exist yet. The single, quickly decaying atoms are not dangerous.
Research and synthesis
Roentgenium serves basic research only. Its value is that it could provide a test for relativistic quantum chemistry. The models for heavy atoms can already be checked on gold. Whether they hold one step further down would be shown by an experiment on roentgenium.
For that, enough atoms with a long enough lifetime would have to be made and their behaviour on a surface measured. This is possible with gold but so far not with roentgenium: the yield is too small and the isotopes decay too quickly. Instead, the decay chains are used to test nuclear models, since roentgenium isotopes occur in the chains of still heavier elements, for example that of nihonium.
The element has nothing to do with X-rays in the medical sense. The name honours the discoverer of a radiation and is no hint of a property.
Quick question
What is the atomic number of roentgenium (Rg)?
FAQ
Which discoverer does the name roentgenium honour?
It is named after Wilhelm Conrad Röntgen, who discovered X-rays in 1895. The name was made official in 2004, years after the element was first made.
Is roentgenium nobler than gold?
Calculations predict so, because relativistic effects bind the electrons more tightly to the nucleus. It has not been measured, as no chemical experiment on roentgenium has been done yet.
Does roentgenium emit X-rays?
Not as a special feature. The name only honours the discoverer of the radiation. Roentgenium decays mainly by alpha emission, like most heavy nuclei.