Roentgenium (Rg)

Roentgenium sits below gold, and calculations suggest relativistic effects would push it further in the same direction — a stable −1 oxidation state, like the auride ion, and possibly a metal that is not yellow but silvery or reddish. It was named for Wilhelm Röntgen, who discovered X-rays; the naming was proposed in 2004, close to the hundredth anniversary. Three atoms were seen in the original 1994 experiment, and the total ever made is still measured in dozens.

Properties

Atomic number

111

Symbol

Rg

Mass number of most stable isotope

[282]

Category

Transition metal

Group

11

Period

7

Block

d-block

Electron configuration

[Rn] 7s² 5f¹⁴ 6d⁹

Electrons per shell

2, 8, 18, 32, 32, 17, 2

Oxidation states

+5, +3, +1, -1

Discovered

1994 by Sigurd Hofmann and colleagues at GSI Darmstadt

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹⁴ 6d⁹

Noble gas shorthand

[Rn] 7s² 5f¹⁴ 6d⁹

Shells

K: 2 · L: 8 · M: 18 · N: 32 · O: 32 · P: 17 · Q: 2

What it is used for

• Research only; no application outside the laboratory

Hazards

• Intensely radioactive; exists only as individual atoms in an accelerator

Melting point, boiling point, density and electronegativity are omitted. The electron configuration is calculated, not observed, and some calculations favour 6d¹⁰ 7s¹. The mass given is the mass number of roentgenium-282, the longest-lived at roughly 100 seconds.

Several physical properties are not listed for roentgenium because no bulk sample has ever existed. Only a handful of atoms have been produced, often with half-lives measured in seconds, so published melting points and densities for elements in this range are calculations rather than measurements. They are omitted rather than presented as observed values.

Neighbours in the table

Group 11

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Roentgenium sits in group 11 with copper, silver, gold.