Roentgenium

2008/9 Schools Wikipedia Selection. Related subjects: Chemical elements

111 darmstadtium ← roentgenium → ununbium Au ↑ Rg ↓ (Uhu) Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	roentgenium, Rg, 111
Element category	transition metals
Group, Period, Block	11, 7, d
Appearance	unknown, predicted colourless
Standard atomic weight	[280] g·mol−1
Electron configuration	predicted [Rn] 5f14 6d9 7s2
Electrons per shell	2, 8, 18, 32, 32, 17, 2
Phase	presumably a solid
CAS registry number	54386-24-2
Selected isotopes
Main article: Isotopes of roentgenium iso NA half-life DM DE ( MeV) DP 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
References

Roentgenium (pronounced /rɛntˈgɛniəm/, /rʌntˈdʒɛniəm/) is a chemical element in the periodic table that has the symbol Rg and atomic number 111.

It is a synthetic element whose most stable known isotope has a mass of 283 and a half-life of ten minutes.

Official discovery

Element 111 was officially discovered by Peter Armbruster, Gottfried Münzenber, and their team working at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany on December 8, 1994. Only three atoms of it were observed (all ²⁷²Rg), by the cold fusion between ⁶⁴Ni ions and a ²⁰⁹Bi target in a linear accelerator:

In 2001, the IUPAC/IUPAP Joint Working Party (JWP) from concluded that there was insufficient evidence for the discovery at that moment in time. The GSI team repeated their experiment in 2000 and detected a further 3 atoms. In their 2003 report, the JWP decided that the GSI team should be acknowledged as the discoverers.

Proposed name

The name roentgenium (Rg) was proposed by the GSI team and was accepted as a permanent name on November 1, 2004 in honour of the German physicist Wilhelm Conrad Röntgen. Previously the element was known under the temporary IUPAC systematic element name unununium (pronounced /ˌjuːnənˈjuːniəm/ or /ˌʌnəˈnʌniəm/), Uuu. Some research has referred to it as eka-gold.

The official baptism took place at GSI, on Friday November 17, 2006, in presence of Annette Schavan, the Federal German Minister of Research.

Electronic structure

Non-relativistic

Roentgenium has 6 full shells, 7 s+5 p+3 d+2 f=17 full subshells, and 111 orbitals:

Bohr model: 2, 8, 18, 32, 32, 18, 1

Quantum mechanical model: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰ 4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰ 6p⁶7s¹5f¹⁴6d¹⁰

Relativistic

The stable group 11 elements, copper, silver, and gold all have an outer electron configuration nd¹⁰(n+1)s¹. For each of these elements, their first excited state has a configuration nd⁹(n+1)s². Due to spin-orbit coupling between the s 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 become silvery. However, as Z increases, the excited levels are stabilised by relativistic effects and in gold the energy gap decreases again and it appears gold. For roentgenium, calculations indicate that the 6d⁹7s² level is stabilised 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.

Extrapolated chemical properties of eka-gold/dvi-silver

Oxidation states

Element 111 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 +II state, whilst silver is predominantly found as Ag(I) and gold as Au(III). Copper(I) and silver(II) are also relatively well-known. Roentgenium is therefore expected to predominantly form a stable +III state.

Chemistry

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. They are both however attacked by the halogens. In addition, silver is attacked by sulfur and hydrogen sulfide, highlighting its higher reactivity 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.

History of synthesis of isotopes by cold fusion

²⁰⁹Bi(⁶⁴Ni,xn)^273−xRg (x=1)

First experiments to synthesize element 111 were performed by the Dubna team in 1986 using this cold fusion reaction. No atoms were identified that could be assigned to atoms of element 111 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. A further 3 atoms were synthesized in 2000. 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.

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.

History of synthesis of isotopes as decay products

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

Chronology of isotope discovery

Chemical yields of isotopes

Cold fusion

The table below provides cross-sections and excitation energies for cold fusion reactions producing roentgenium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.

Isotopes

Five isotopes of roentgenium are known. The longest-lived of these is ²⁸⁰Rg, which decays through alpha decay and has a halflife of 3.6 seconds. The shortest-lived isotope is ²⁷²Rg, which decays through alpha decay and has a halflife of 1.6 ms.

Isomerism in roentgenium nuclides

²⁷⁴Rg

Two atoms of ²⁷⁴Rg have been observed in the decay chains starting with ²⁷⁸113. 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 has 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.

Future experiments

To date there has been no attempt to synthesise roentgenium in hot fusion reactions. It has been mentioned by the Dubna team that they could complete their Ca-48 projectile program by studying the reaction