Roentgenium (Rg)

Roentgenium (symbol Rg) is the chemical element with atomic number 111: a superheavy element whose properties are still unknown, radioactive, made artificially, with an atomic mass of 282 u. Discovered in 1994 (Sigurd Hofmann et al. (GSI)).

Roentgenium honors Wilhelm Röntgen, who discovered X-rays in 1895 and received the first Nobel Prize in Physics. Sitting below gold in the table, it could in theory share some of its traits, but no one has ever checked. Only a few dozen atoms have been produced. Its most stable known isotope, roentgenium-282, has a half-life of around two minutes.

Key facts

Atomic number: 111
Symbol: Rg
French name: Roentgenium
Atomic mass: 282 u
Molar mass: [282] g/mol
Family: Unknown properties
Position: period 7, group 11, d-block
State at 0 °C: Unknown
First ionization energy: 1,020 kJ/mol
Electron configuration: [Rn] 5f¹⁴ 6d⁹ 7s²
Radioactive: yes
Discovery: 1994, Sigurd Hofmann et al. (GSI)

Origin of the name

In honor of Wilhelm Röntgen, discoverer of X-rays.

What does roentgenium look like?

Never observed. Calculations suggest it would be silvery rather than golden: gold's color comes from relativistic effects — linked to the speed of the electrons close to the nucleus — which would play out differently here.

Where is roentgenium found?

Absent from nature.

How is roentgenium produced?

GSI created it by bombarding a bismuth-209 target with nickel-64 ions. Its longest-lived isotopes come from the decay of nihonium and tennessine.

Top producers

Germany (GSI Darmstadt)
Japan (RIKEN)
Russia (Dubna)

What is roentgenium used for?

Basic research only

In everyday life

None — it exists only for moments in the lab

Role in living things

No biological role.

Hazards of roentgenium

Radioactive, but produced atom by atom: no practical danger.

Cosmic origin

Human-made: Does not exist (or barely) in nature: synthesized in a reactor or accelerator.

History of roentgenium

On December 8, 1994, a month after darmstadtium, Sigurd Hofmann's team at GSI observed three atoms of roentgenium-272. The discovery was confirmed by RIKEN, and the name was approved in 2004.

Did you know?

Its name became official in 2004, more than a century after the discovery of X-rays.
Before being named, it was provisionally called “unununium” (one-one-one), under IUPAC's rule based on the digits of the atomic number.
Though it is gold's cousin, it is worth nothing: no atom has ever survived more than a few minutes.

Isotopes of roentgenium

No stable isotopes; roentgenium isotopes decay within a few milliseconds to a few minutes.

roentgenium-272: radioactive, half-life 4.5 ms. The element's first synthesized isotope, in 1994.
roentgenium-282: radioactive, half-life 1.7 min. Among the longest-lived known.

Related elements

Same family (unknown properties): Meitnerium (Mt), Darmstadtium (Ds), Copernicium (Cn), Nihonium (Nh), Flerovium (Fl), Moscovium (Mc), Livermorium (Lv), Tennessine (Ts), Oganesson (Og).

Same column (group 11): Copper (Cu), Silver (Ag), Gold (Au).