Roentgenium (111)

Roentgenium [RUNT-GEE-NEE-UM] is a chemical element with the symbol Rg and atomic number 111. It is an extremely radioactive synthetic element (an element that can be created in a laboratory but is not found in nature); the most stable known isotope, roentgenium-281, has a half-life of 26 seconds. Roentgenium was first created on December 8, 1994 by the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany. It is named after the physicist Wilhelm Röntgen (also spelled Roentgen).

In the periodic table, it is a d-block transactinide element. It is a member of the 7th period and is placed in the group 11 elements, although no chemical experiments have been carried out to confirm that it behaves as the heavier homologue to gold in group 11. Roentgenium is calculated to have similar properties to its lighter homologues, copper, silver, and gold, although it may show some differences from them.

Name: Roentgenium Symbol: Rg Atomic number: 111 Atomic weight: [ 280 ] Standard state: presumably a solid at 298 K CAS Registry ID: 54386-24-2

Group in periodic table: 11 Period in periodic table: 7 Block in periodic table: d-block Color: unknown, but probably metallic and silvery white or grey in appearance Classification: Metallic

Historical information

Element 111, roentgenium, was discovered towards the end of 1994 at the GSI in Darmstadt, Germany. Three atoms of an isotope ²⁷²Uuu were produced in reactions between ²⁰⁹Bi targets and ⁶⁴Ni projectiles. To achieve this, the nickel atoms were accelerated to high energies by the heavy ion accelerator UNILAC at GSI and directed onto a lead target.

Roentgenium was first synthesized by an international team led by Sigurd Hofmann at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany, on December 8, 1994. The team bombarded a target of bismuth-209 with accelerated nuclei of nickel-64 and detected a single atom of the isotope roentgenium-272:

In 2001, the IUPAC/IUPAP Joint Working Party (JWP) concluded that there was insufficient evidence for the discovery at that time. The GSI team repeated their experiment in 2002 and detected three more atoms. In their 2003 report, the JWP decided that the GSI team should be acknowledged for the discovery of this element.

The name roentgenium (Rg) was suggested by the GSI team in 2004, to honor the German physicist Wilhelm Conrad Röntgen, who discovered X-rays in 1865. This name was accepted by IUPAC on November 1, 2004.

Physical properties

• Body Centered cubic crystal structure
• Density of solid: 28.7 (predicted) g cm^-3

Orbital properties

• Ground state electron configuration:  [Rn].5f¹⁴.6d¹⁰.7s¹ (a guess based upon that of gold)
• Shell structure:  2.8.18.32.32.18.1
• Term symbol:   ²S_1/2 (a guess based upon guessed electronic structure)
• Pauling electronegativity: no data (Pauling units)
• First ionization energy (estimated): 1022.7 kJ mol^-1
• Second ionization energy (estimated): 2074.4 kJ mol^-1

Isolation

Only a few atoms of element 111, roentgenium, have ever been made through a nuclear reaction involving fusion of an isotope of bismuth, ²⁰⁹Bi, with one of nickel, ⁶⁴Ni.

²⁰⁹Bi + ⁶⁴Ni → ²⁷²Rg + ¹n

Isolation of an observable quantity has never been achieved, and may well never be.