Ununhexium is the temporary name of a
syntheticIn chemistry, a synthetic element is a chemical element that is too unstable to occur naturally on Earth, and therefore has to be created artificially. So far 30 synthetic elements have been discovered—that is, synthesized...
superheavy element with the temporary symbol
Uuh and
atomic numberIn 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...
116. There is no proposed name yet although
moscovium (after
Moscow OblastMoscow Oblast , or Podmoskovye , is a federal subject of Russia . Its area, at , is relatively small compared to other federal subjects, but it is one of the most densely populated regions in the country and, with the 2010 population of 7,092,941, is the second most populous federal subject...
in
RussiaRussia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, where the place of discovery,
DubnaDubna 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...
, is located) has been discussed in the media.
It is placed as the heaviest member of group 16 (VIA) although a sufficiently stable isotope is not known at this time to allow chemical experiments to confirm its position as the heavier homologue to
poloniumPolonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive element, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for...
.
It was first detected in 2000 and since the discovery about 30 atoms of ununhexium have been produced, either directly or as a decay product of
ununoctiumUnunoctium is the temporary IUPAC name for the transactinide element having the atomic number 118 and temporary element symbol Uuo. It is also known as eka-radon or element 118, and on the periodic table of the elements it is a p-block element and the last one of the 7th period. Ununoctium is...
, and are associated with decays from the four neighbouring isotopes with masses 290–293. The most stable isotope to date is ununhexium-293 with a
half-lifeHalf-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 ~60 ms.
Discovery
On July 19, 2000, scientists at
DubnaDubna 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...
(
JINRThe Joint Institute for Nuclear Research, JINR , in Dubna, Moscow Oblast , Russia, is an international research centre for nuclear sciences, with 5500 staff members, 1200 researchers including 1000 Ph.D.s from eighteen member states The Joint Institute for Nuclear Research, JINR , in Dubna, Moscow...
) detected a single decay from an atom of ununhexium following the irradiation of a Cm-248 target with Ca-48 ions. The results were published in December, 2000. This 10.54 MeV alpha-emitting activity was originally assigned to
292Uuh due to the correlation of the daughter to previously assigned
288Uuq. However, that assignment was later altered to
289Uuq, and hence this activity was correspondingly changed to
293Uuh. Two further atoms were reported by the institute during their second experiment between April–May 2001.
In the same experiment they also detected a decay chain which corresponded to the first observed decay of
ununquadiumUnunquadium is the temporary name of a radioactive chemical element with the temporary symbol Uuq and atomic number 114. There is no proposed name yet, although flerovium has been discussed in the media.About 80 decays of atoms of...
and assigned to
289Uuq.
This activity has not been observed again in a repeat of the same reaction. However, its detection in this series of experiments indicates the possibility of the decay of an isomer of ununhexium, namely
293bUuh, or a rare decay branch of the already discovered isomer,
293aUuh, in which the first
alpha particleAlpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
was missed. Further research is required to positively assign this activity.
The team repeated the experiment in April–May 2005 and detected 8 atoms of ununhexium. The measured decay data confirmed the assignment of the discovery
isotopeIsotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
as
293Uuh. In this run, the team also observed
292Uuh in the 4n channel for the first time.
In May 2009, the Joint Working Party reported on the discovery of copernicium and acknowledged the discovery of the isotope
283Cn. This implied the
de facto discovery of ununhexium, as
291Uuh (see below), from the acknowledgment of the data relating to the granddaughter
283Cn, although the actual discovery experiment may be determined as that above.
In 2011, the IUPAC evaluated the Dubna team results and accepted them as a reliable identification of element 116.
Naming
Ununhexium is historically known as
ekaProfessor Dmitri Mendeleev published the first Periodic Table of the Atomic Elements in 1869 based on properties which appeared with some regularity as he laid out the elements from lightest to heaviest....
-poloniumPolonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive element, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for...
.
Ununhexium (Uuh) is a temporary IUPAC
systematic element nameA 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...
. Scientists usually refer to the element simply as
element 116 (or E116). According to IUPAC recommendations, the discoverer(s) of a new element has the right to suggest a name.
The discovery of ununhexium was recognized by JWG of IUPAC on 1 June 2011, along with that of ununquadium. According to the vice-director of JINR, the Dubna team would like to name element 116
moscovium, after the
Moscow OblastMoscow Oblast , or Podmoskovye , is a federal subject of Russia . Its area, at , is relatively small compared to other federal subjects, but it is one of the most densely populated regions in the country and, with the 2010 population of 7,092,941, is the second most populous federal subject...
in which Dubna is located.
Current and future experiments
The GSI was to be running an experiment (June 24 – July 25, 2010) to study the formation of
293,292Uuh in the
248Cm(
48Ca,xn) reaction as a first step in their future program with a
248Cm target, aiming towards a synthesis of
unbiniliumUnbinilium , also called eka-radium or element 120, is the temporary, systematic element name of a hypothetical chemical element in the periodic table that has the temporary symbol Ubn and has the atomic number 120....
.
The team at Dubna have indicated plans to synthesize ununhexium using the reaction between
plutoniumPlutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
-244 and titanium-50. This experiment will allow them to assess the feasibility of using projectiles with Z > 20 required in the synthesis of superheavy elements with Z>118. Although initially scheduled for 2008, the reaction looking at the synthesis of evaporation residues has not been conducted to date.
There are also plans to repeat the Cm-248 reaction at different projectile energies in order to probe the 2n channel, leading to the new
isotopeIsotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
294Uuh. In addition, they have future plans to complete the
excitation functionExcitation function is a term used in nuclear physics to describe a graphical plot of the yield of a radionuclide or reaction channel as a function of the bombarding projectile energy or the calculated excitation energy of the compound nucleus....
of the 4n channel product,
292Uuh, which will allow them to assess the stabilizing effect of the N=184 shell on the yield of evaporation residues.
Target-projectile combinations leading to Z=116 compound nuclei
The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with atomic number 116.
| Target | Projectile | CN | Attempt result |
| 208Pb |
82Se |
290Uuh |
|
| 232Th |
58Fe |
290Uuh |
|
| 238U |
54Cr |
292Uuh |
|
| 244Pu |
50Ti |
294Uuh |
|
| 248Cm |
48Ca |
296Uuh |
|
| 246Cm |
48Ca |
294Uuh |
|
| 245Cm |
48Ca |
293Uuh |
|
| 249Cf |
40Ar |
289Uuh |
|
208Pb(82Se,xn)290−xUuh
In 1998, the team at GSI attempted the synthesis of
290Uuh as a radiative capture (
x=0) product. No atoms were detected providing a cross section limit of 4.8 pb.
Hot fusion
This section deals with the synthesis of nuclei of ununhexium by so-called "hot" fusion reactions. These are processes which create compound nuclei at high excitation energy (~40–50 MeV, hence "hot"), leading to a reduced probability of survival from fission. The excited nucleus then decays to the ground state via the emission of 3–5 neutrons. Fusion reactions utilizing
48Ca nuclei usually produce compound nuclei with intermediate excitation energies (~30–35 MeV) and are sometimes referred to as "warm" fusion reactions. This leads, in part, to relatively high yields from these reactions.
238U(54Cr,xn)292−xUuh
There are sketchy indications that this reaction was attempted by the team at GSI in 2006. There are no published results on the outcome, presumably indicating that no atoms were detected. This is expected from a study of the systematics of cross sections for
238U targets.
248Cm(48Ca,xn)296−xUuh (x=3,4)
The first attempt to synthesise ununhexium was performed in 1977 by Ken Hulet and his team at the Lawrence Livermore National Laboratory (LLNL). They were unable to detect any atoms of ununhexium. Yuri Oganessian and his team at the Flerov Laboratory of Nuclear Reactions (FLNR) subsequently attempted the reaction in 1978 and were met by failure. In 1985, a joint experiment between Berkeley and Peter Armbruster's team at GSI, the result was again negative with a calculated cross-section limit of 10–100 pb.
In 2000, Russian scientists at Dubna finally succeeded in detecting a single atom of ununhexium, assigned to the isotope
292Uuh.
In 2001, they repeated the reaction and formed a further 2 atoms in a confirmation of their discovery experiment. A third atom was tentatively assigned to
293Uuh on the basis of a missed parental alpha decay.
In April 2004, the team ran the experiment again at higher energy and were able to detect a new decay chain, assigned to
292Uuh. On this basis, the original data were reassigned to
293Uuh. The tentative chain is therefore possibly associated with a rare decay branch of this isotope. In this reaction, 2 further atoms of
293Uuh were detected.
245Cm(48Ca,xn)293−x116 (x=2,3)
In order to assist in the assignment of isotope mass numbers for ununhexium, in March–May 2003 the Dubna team bombarded a
245Cm target with
48Ca ions. They were able to observe two new isotopes, assigned to
291Uuh and
290Uuh. This experiment was successfully repeated in Feb–March 2005 where 10 atoms were created with identical decay data to those reported in the 2003 experiment.
As a decay product
Ununhexium has also been observed in the decay of ununoctium. In October 2006 it was announced that 3 atoms of
ununoctiumUnunoctium is the temporary IUPAC name for the transactinide element having the atomic number 118 and temporary element symbol Uuo. It is also known as eka-radon or element 118, and on the periodic table of the elements it is a p-block element and the last one of the 7th period. Ununoctium is...
had been detected by the bombardment of
californiumCalifornium is a radioactive metallic chemical element with the symbol Cf and atomic number 98. The element was first made in the laboratory in 1950 by bombarding curium with alpha particles at the University of California, Berkeley. It is the ninth member of the actinide series and was the...
-249 with calcium-48 ions, which then rapidly decayed into ununhexium.
The observation of
290Uuh allowed the assignment of the product to
294Uuo and proved the synthesis of
ununoctiumUnunoctium is the temporary IUPAC name for the transactinide element having the atomic number 118 and temporary element symbol Uuo. It is also known as eka-radon or element 118, and on the periodic table of the elements it is a p-block element and the last one of the 7th period. Ununoctium is...
.
Fission of compound nuclei with Z=116
Several experiments have been performed between 2000–2006 at the Flerov laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nuclei
296,294,290Uuh. Four nuclear reactions have been used, namely
248Cm+
48Ca,
246Ca+
48Ca,
244Pu+
50Ti and
232Th+
58Fe. The results have revealed how nuclei such as this fission predominantly by expelling closed shell nuclei such as
132Sn (Z=50, N=82). It was also found that the yield for the fusion-fission pathway was similar between
48Ca and
58Fe projectiles, indicating a possible future use of
58Fe projectiles in superheavy element formation.In addition, in comparative experiments synthesizing
294Uuh using
48Ca and
50Ti projectiles, the yield from fusion-fission was ~3x less for
50Ti, also suggesting a future use in SHE production
289Uuh
In 1999, researchers at
Lawrence Berkeley National LaboratoryThe Lawrence Berkeley National Laboratory , is a U.S. Department of Energy national laboratory conducting unclassified scientific research. It is located on the grounds of the University of California, Berkeley, in the Berkeley Hills above the central campus...
announced the synthesis of
293Uuo (see
ununoctiumUnunoctium is the temporary IUPAC name for the transactinide element having the atomic number 118 and temporary element symbol Uuo. It is also known as eka-radon or element 118, and on the periodic table of the elements it is a p-block element and the last one of the 7th period. Ununoctium is...
), in a paper published in
Physical Review Letters. The claimed isotope
289Uuh decayed by 11.63 MeV alpha emission with a half-life of 0.64 ms. The following year, they published a
retractionA retraction is a public statement, by the author of an earlier statement, that withdraws, cancels, refutes, diametrically reverses the original statement or ceases and desists from publishing the original statement...
after other researchers were unable to duplicate the results. In June 2002, the director of the lab announced that the original claim of the discovery of these two elements had been based on data fabricated by the principal author
Victor NinovVictor Ninov is a former researcher in the nuclear chemistry group at Lawrence Berkeley National Laboratory who was alleged to have fabricated the evidence used to claim the creation of ununoctium and ununhexium....
. As such, this isotope of ununhexium is currently unknown.
Chronology of isotope discovery
| Isotope | Year discovered | Discovery reaction |
| 290Uuh |
2002 |
249Cf(48Ca,3n) |
| 291Uuh |
2003 |
245Cm(48Ca,2n) |
| 292Uuh |
2004 |
248Cm(48Ca,4n) |
| 293Uuh |
2000 |
248Cm(48Ca,3n) |
Hot fusion
The table below provides cross-sections and excitation energies for hot fusion reactions producing ununhexium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.
| Projectile | Target | CN | 2n | 3n | 4n | 5n |
| 48Ca |
248Cm |
296Uuh |
|
1.1 pb, 38.9 MeV |
3.3 pb, 38.9 MeV |
|
| 48Ca |
245Cm |
293Uuh |
0.9 pb, 33.0 MeV |
3.7 pb, 37.9 MeV |
|
Decay characteristics
Theoretical calculation in a quantum tunneling model supports the experimental data relating to the synthesis of
293,292Uuh.
Evaporation residue cross sections
The below table contains various targets-projectile combinations for which calculations have provided estimates for cross section yields from various neutron evaporation channels. The channel with the highest expected yield is given.
DNS = Di-nuclear system; σ = cross section
| Target | Projectile | CN | Channel (product) | σmax | Model | Ref |
| 208Pb |
82Se |
290Uuh |
1n (289Uuh) |
0.1 pb |
DNS |
|
| 208Pb |
79Se |
287Uuh |
1n (286Uuh) |
0.5 pb |
DNS |
|
| 238U |
54Cr |
292Uuh |
2n (290Uuh) |
0.1 pb |
DNS |
|
| 250Cm |
48Ca |
298Uuh |
4n (294Uuh) |
5 pb |
DNS |
|
| 248Cm |
48Ca |
296Uuh |
4n (292Uuh) |
2 pb |
DNS |
|
| 247Cm |
48Ca |
295Uuh |
3n (292Uuh) |
3 pb |
DNS |
|
| 245Cm |
48Ca |
293Uuh |
3n (290Uuh) |
1.5 pb |
DNS |
|
Oxidation states
Ununhexium is projected to be the fourth member of the 7p series of non-metals and the heaviest member of group 16 (VIA) in the Periodic Table, below
poloniumPolonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive element, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for...
. The group oxidation state of +VI is known for all the members apart from oxygen which lacks available d-
orbitalsAn atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...
for expansion and is limited to a maximum +II state, exhibited in the fluoride OF
2. The +IV is known for
sulfurSulfur 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...
,
seleniumSelenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...
,
tellurium, and
poloniumPolonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive element, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for...
, undergoing a shift in stability from reducing for S(IV) and Se(IV) to oxidizing in Po(IV). Tellurium(IV) is the most stable for this element. This suggests a decreasing stability for the higher oxidation states as the group is descended and ununhexium should portray an oxidizing +IV state and a more stable +II state. The lighter members are also known to form a −II state as
oxideAn oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....
,
sulfideA sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
,
selenideA selenide is a chemical compound in which selenium serves as an anion with oxidation number of −2 , much as sulfur does in a sulfide. The chemistry of the selenides and sulfides are similar....
,
tellurideThe telluride ion is Te2−. It is the final stable member of the series of dianions O2−, S2−, and Se2− ....
, and
polonideA polonide is a chemical compound of the radioactive element polonium with any other element except a halogen. Polonides are usually prepared by a direct reaction between the elements...
.
Chemistry
The possible chemistry of ununhexium can be extrapolated from that of
poloniumPolonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive element, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for...
. It should therefore undergo oxidation to a dioxide, UuhO
2, although a trioxide, UuhO
3 is plausible, but unlikely. The stability of a +II state should manifest itself in the formation of a simple monoxide, UuhO. Fluorination will likely result in a tetrafluoride, UuhF
4 and/or a difluoride, UuhF
2.
ChlorinationChlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water...
and bromination may well stop at the corresponding dihalides, UuhCl
2 and UuhBr
2. Oxidation by
iodineIodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
should certainly stop at UuhI
2 and may even be
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 this element.
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