Roentgenium
Encyclopedia
Roentgenium 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, which decays by spontaneous fission, like many other N=170 isotone
s.
(GSI) in Darmstadt
, Germany
, on December 8, 1994.
Only three atom
s of it were observed (all 272Rg), by the cold fusion between nickel
ions and a bismuth
target in a linear accelerator:
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.
in 2004, and approved on November 4, 2011. Previously the element was known under the temporary IUPAC systematic element name
unununium, Uuu.
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. 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.
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.
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.
, 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.
character. Silver
and gold
are both inert
to oxygen
, but are attacked by the halogen
s. 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.
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
with the symbol Rg and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
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
Homology (chemistry)
In chemistry, homology refers to the appearance of homologues. A homologue is a compound belonging to a series of compounds differing from each other by a repeating unit, such as a methylene group, a peptide residue, etcetera....
of gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
.
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
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of ~26 seconds, which decays by spontaneous fission, like many other N=170 isotone
Isotone
Two nuclides are isotones if they have the same neutron number N, but different proton number Z. For example, boron-12 and carbon-13 nuclei both contain 7 neutrons, and so are isotones. Similarly, S-36, Cl-37, Ar-38, K-39, and Ca-40 nuclei are all isotones of 20 because they all contain 20 neutrons...
s.
Official discovery
Roentgenium was officially discovered by an international team led by Sigurd Hofmann at the Gesellschaft für SchwerionenforschungGesellschaft für Schwerionenforschung
The GSI Helmholtz Centre for Heavy Ion Research GmbH in the Wixhausen suburb of Darmstadt, Germany is a federally and state co-funded heavy ion research center. The current director of GSI is Horst Stöcker who succeeded Walter F...
(GSI) in Darmstadt
Darmstadt
Darmstadt is a city in the Bundesland of Hesse in Germany, located in the southern part of the Rhine Main Area.The sandy soils in the Darmstadt area, ill-suited for agriculture in times before industrial fertilisation, prevented any larger settlement from developing, until the city became the seat...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, on December 8, 1994.
Only three atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
s of it were observed (all 272Rg), by the cold fusion between nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
ions and a bismuth
Bismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...
target in a linear accelerator:
- + → +
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.
Naming
The name roentgenium (Rg) was recommended by the GSI team in honor of the German physicist Wilhelm Conrad RöntgenWilhelm Conrad Röntgen
Wilhelm Conrad Röntgen was a German physicist, who, on 8 November 1895, produced and detected electromagnetic radiation in a wavelength range today known as X-rays or Röntgen rays, an achievement that earned him the first Nobel Prize in Physics in 1901....
in 2004, and approved on November 4, 2011. Previously the element was known under the temporary IUPAC systematic element name
Systematic element name
A systematic element name is the temporary name and symbol assigned to newly synthesized and not yet synthesized chemical elements. In chemistry, a transuranic element receives a permanent name and symbol only after its synthesis has been confirmed. In some cases, this has been a protracted and...
unununium, Uuu.
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.| Target | Projectile | CN | Attempt result |
|---|---|---|---|
| 208Pb | 65Cu | 273Rg | |
| 209Bi | 64Ni | 273Rg | |
| 232Th | 45Sc | 277Rg | |
| 231Pa | 48Ca | 279Rg | |
| 238U | 41K | 280Rg | |
| 237Np | 40Ar | 277Rg | |
| 244Pu | 37Cl | 281Rg | |
| 243Am | 36S | 279Rg | |
| 248Cm | 31P | 279Rg | |
| 249Bk | 30Si | 279Rg | |
| 249Cf | 27Al | 276Rg |
Cold fusion
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
Dubna
Dubna is a town in Moscow Oblast, Russia. It has a status of naukograd , being home to the Joint Institute for Nuclear Research, an international nuclear physics research centre and one of the largest scientific foundations in the country. It is also home to MKB Raduga, a defence aerospace company...
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
Barn (unit)
A barn is a unit of area. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process, and is best understood as a measure of the...
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
RIKEN
is a large natural sciences research institute in Japan. Founded in 1917, it now has approximately 3000 scientists on seven campuses across Japan, the main one in Wako, just outside Tokyo...
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.
As a decay product
Isotopes of roentgenium have also been observed in the decay of heavier elements. Observations to date are outlined in the table below:| Evaporation residue | Observed Rg isotope |
|---|---|
| 288Uup | 280Rg |
| 287Uup | 279Rg |
| 282Uut | 278Rg |
| 278Uut | 274Rg |
Chronology of isotope discovery
| Isotope | Year discovered | Discovery reaction |
|---|---|---|
| 272Rg | 1994 | 209Bi(64Ni,n) |
| 273Rg | unknown | |
| 274Rg | 2004 | 209Bi(70Zn,n) |
| 275Rg | unknown | |
| 276Rg | unknown | |
| 277Rg | unknown | |
| 278Rg | 2006 | 237Np(48Ca,3n) |
| 279Rg | 2003 | 243Am(48Ca,4n) |
| 280Rg | 2003 | 243Am(48Ca,3n) |
| 281Rg | 2009 | 249Bk(48Ca,4n) |
| 282Rg | 2009 | 249Bk(48Ca,3n) |
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-lifeHalf-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 1.6 ms whilst recent data from RIKEN have given a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
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.
Cold fusion
The table below provides cross-sections and excitation energies for cold fusion reactions producing roentgenium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.| Projectile | Target | CN | 1n | 2n | 3n |
|---|---|---|---|---|---|
| 64Ni | 209Bi | 273Rg | 3.5 pb, 12.5 MeV | ||
| 65Cu | 208Pb | 273Rg | 1.7 pb, 13.2 MeV |
Electronic structure (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, 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.Oxidation states
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 copperCopper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
, and gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
. 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
The heavier members of this group are well known for their lack of reactivity or nobleNoble metal
Noble metals are metals that are resistant to corrosion and oxidation in moist air, unlike most base metals. They tend to be precious, often due to their rarity in the Earth's crust...
character. Silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
and gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
are both inert
Inert
-Chemistry:In chemistry, the term inert is used to describe a substance that is not chemically reactive.The noble gases were previously known as inert gases because of their perceived lack of participation in any chemical reactions...
to oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, but are attacked by the halogen
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
s. In addition, silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
is attacked by sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
and hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
, highlighting its higher reactivity compared to gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
. 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.