darmstadtium ← roentgenium → copernicium Au ↑ Rg ↓ (Uhu) 111Rg Periodic table
Appearance
unknown
General properties
Name, symbol, number	roentgenium, Rg, 111
Pronunciation	i/rʌntˈɡɛniəm/ runt-GEN-ee-əm or /rɛntˈɡɛniəm/ rent-GEN-ee-əm
Element category	unknown
Group, period, block	11, 7, d
Standard atomic weight	[281]
Electron configuration	[Rn] 5f14 6d9 7s2 (predicted)[1]
Electrons per shell	2, 8, 18, 32, 32, 17, 2 (predicted)[1] (Image)
Physical properties
Phase	Unknown
Atomic properties
Oxidation states	−1, +1, +3, +5[2] (a guess based on that of gold)
Covalent radius	121 (estimated)[3] pm
Miscellanea
CAS registry number	54386-24-2
Most stable isotopes
Main article: Isotopes of roentgenium
iso NA half-life DM DE (MeV) DP 282Rg syn 0.5 s α 9.00 278Mt 281Rg syn 26 s SF 280Rg syn 3.6 s α 9.75 276Mt 279Rg syn 170 ms α 10.37 275Mt 278Rg syn 4.2 ms α 10.69 274Mt 274Rg syn 15 ms α 11.23 270Mt 272Rg syn 1.6 ms α 11.02,10.82 268Mt
v t e · r

Roentgenium (formerly unununium) is a synthetic radioactive chemical element with the symbol Rg and atomic number 111. It is placed as the heaviest member of the group 11 (IB) elements, although a sufficiently stable isotope has not yet been produced in a sufficient amount that would confirm this position as a heavier homologue of gold.

Roentgenium was first observed in 1994 and several isotopes have been synthesized since its discovery. The most stable known isotope is ²⁸¹Rg with a half-life of ~26 seconds,^[4] which decays by spontaneous fission, like many other N=170 isotones.

History[link]

Official discovery[link]

Roentgenium was officially discovered by an international team led by Sigurd Hofmann at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany, on December 8, 1994.^[5] Only three atoms of it were observed (all ²⁷²Rg), by the cold fusion between nickel ions and a bismuth target in a linear accelerator:

209
83Bi + 64
28Ni → 272
111Rg + 1
0n

In 2001, the IUPAC/IUPAP Joint Working Party (JWP) concluded that there was insufficient evidence for the discovery at that time.^[6] The GSI team repeated their experiment in 2002 and detected three more atoms.^[7][8] In their 2003 report, the JWP decided that the GSI team should be acknowledged for the discovery of this element.^[9]

Naming[link]

The name roentgenium (Rg) was recommended by the GSI team^[10] in honor of the German physicist (and X-ray discoverer) Wilhelm Conrad Röntgen in 2004.^[11] This name was accepted by IUPAC on November 1, 2004 and approved by IUPAP on November 4, 2011.^[12] Previously, the element was known under the temporary IUPAC systematic element name unununium with symbol Uuu.^[13]

Nucleosynthesis[link]

Target-projectile combinations leading to Z=111 compound nuclei

The below table contains various combinations of targets and projectiles (both at max no. of neutrons) which could be used to form compound nuclei with Z=111.

Cold fusion[link]

This section deals with the synthesis of nuclei of roentgenium by so-called "cold" fusion reactions. These are processes which create compound nuclei at low excitation energy (~10–20 MeV, hence "cold"), leading to a higher probability of survival from fission. The excited nucleus then decays to the ground state via the emission of one or two neutrons only.

²⁰⁹Bi(⁶⁴Ni,xn)^273−xRg (x=1)

First experiments to synthesize roentgenium were performed by the Dubna team in 1986 using this cold fusion reaction. No atoms were identified that could be assigned to atoms of roentgenium and a production cross-section limit of 4 pb was determined. After an upgrade of their facilities, the team at GSI successfully detected 3 atoms of ²⁷²Rg in their discovery experiment.^[5] A further 3 atoms were synthesized in 2000.^[7] The discovery of roentgenium was confirmed in 2003 when a team at RIKEN measured the decays of 14 atoms of ²⁷²Rg during the measurement of the 1n excitation function.^[14]

²⁰⁸Pb(⁶⁵Cu,xn)^273−xRg (x=1)

In 2004, as part of their study of odd-Z projectiles in cold fusion reactions, the team at LBNL detected a single atom of ²⁷²Rg in this new reaction.^[15][16]

As decay product[link]

Isotopes of roentgenium have also been observed in the decay of heavier elements. Observations to date are outlined in the table below:

Isotopes[link]

Chronology of isotope discovery

Nuclear isomerism[link]

²⁷⁴Rg

Two atoms of ²⁷⁴Rg have been observed in the decay chains starting with ²⁷⁸Uut. The two events occur with different energies and with different lifetimes. In addition, the two entire decay chains appear to be different. This suggests the presence of two isomeric levels but further research is required.

²⁷²Rg

The direct production of ²⁷²Rg has provided four alpha lines at 11.37, 11.03, 10.82, and 10.40 MeV. The GSI measured a half-life of 1.6 ms whilst recent data from RIKEN have given a half-life of 3.8 ms. The conflicting data may be due to isomeric levels but the current data are insufficient to come to any firm assignments.

Chemical properties[link]

Electronic structure (relativistic)[link]

The stable group 11 elements, copper, silver, and gold all have an outer electron configuration nd¹⁰(n+1)s¹. For each of these elements, the first excited state of their atoms has a configuration nd⁹(n+1)s². Due to spin-orbit coupling between the d electrons, this state is split into a pair of energy levels. For copper, the difference in energy between the ground state and lowest excited state causes the metal to appear reddish. For silver, the energy gap widens and it becomes silvery. However, as Z increases, the excited levels are stabilized by relativistic effects and in gold the energy gap decreases again and it appears gold. For roentgenium, calculations indicate that the 6d⁹7s² level is stabilized to such an extent that it becomes the ground state. The resulting energy difference between the new ground state and the first excited state is similar to that of silver and roentgenium is expected to be silvery in appearance.^[19]

Extrapolated chemical properties[link]

Oxidation states[link]

Roentgenium is projected to be the ninth member of the 6d series of transition metals and the heaviest member of group 11 (IB) in the Periodic Table, below copper, silver, and gold. Each of the members of this group show different stable states. Copper forms a stable +2 state, while silver is predominantly found as silver(I) and gold as gold(I) or gold(III). Copper(I) and silver(II) are also relatively well-known. Roentgenium is therefore expected to predominantly form a stable +3 state. Gold also forms a somewhat stable -1 state due to relativistic effects, and roentgenium may do so as well.

Chemistry[link]

The heavier members of this group are well known for their lack of reactivity or noble character. Silver and gold are both inert to oxygen, but are attacked by the halogens. In addition, silver is attacked by sulfur and hydrogen sulfide, highlighting its higher reactivity compared to gold. Roentgenium is expected to be even more noble than gold and can be expected to be inert to oxygen and halogens. The most-likely reaction is with fluorine to form a trifluoride, RgF₃.

See also[link]

• Island of stability

References[link]

External links[link]

Wikimedia Commons has media related to: Roentgenium

• WebElements.com: Roentgenium
• IUPAC: Proposal of name roentgenium for element 111
• IUPAC: Element 111 is named roentgenium
• Apsidium: Roentgenium 111

vep:Röntgenii