Ununtrium

Ununtrium is a chemical element with atomic number 113. It has a temporary name and temporary symbol Uut. It is an extremely radioactive synthetic element (an element that can be created in a laboratory but is not found in nature); its most stable known isotope, ununtrium-286, has a half-life of 20 seconds. It is also known as eka-thallium or simply element 113. Ununtrium was first created in 2003 by the Joint Institute for Nuclear Research in Dubna, Russia, although this discovery is still awaiting confirmation by IUPAC.

In the periodic table, it is a p-block transactinide element. It is a member of the 7th period and is placed in the boron group, although it has not been confirmed to behave as the heavier homologue to thallium in the boron group. Ununtrium is calculated to have some similar properties to its lighter homologues, boron, aluminium, gallium, indium, and thallium, although it should also show several major differences from them. Unlike all the other p-block elements, it is predicted to show some transition metal character.

§History

§Dubnaâ€"Livermore collaboration

The first report of ununtrium was in August 2003, when it was identified as an alpha decay product of element 115, ununpentium. These results were published on February 1, 2004, by a team composed of Russian scientists at Dubna (Joint Institute for Nuclear Research), and American scientists at the Lawrence Livermore National Laboratory:

243
95Am + 48
20Ca â†' 288
115Uup + 3 1
0n â†' 284
113Uut + α

243
95Am + 48
20Ca â†' 287
115Uup + 4 1
0n â†' 283
113Uut + α

The Dubnaâ€"Livermore collaboration has strengthened their claim for the discovery of ununtrium by conducting chemical experiments on ²⁶⁸Db, the final decay product of ²⁸⁸Uup. This was valuable as none of the nuclides in this decay chain were previously known, so that their claim was not supported by any previously obtained experimental data (as none existed), and chemical experimentation would strengthen the case for their claim. In June 2004 and again in December 2005, this dubnium isotope was successfully identified by extracting the final decay products, measuring spontaneous fission (SF) activities and using chemical identification techniques to confirm that they behave like a group 5 element (as dubnium is known to be in group 5 of the periodic table). Both the half-life and decay mode were confirmed for the proposed ²⁶⁸Db which lends support to the assignment of the parent and daughter nuclei to ununpentium and ununtrium respectively. Further experiments at Dubna in 2005 have fully confirmed the decay data for ununpentium and ununtrium, but in 2011, the IUPAC/IUPAP Joint Working Party (JWP) did not recognize the two elements as having been discovered because current theory could not distinguish between group 4 and group 5 elements by their chemical properties with sufficient confidence, and the identification of the daughter dubnium isotope was the most important factor in confirming the discovery of ununpentium and ununtrium. Furthermore, the decay properties of all the nuclei in the decay chain of ununpentium had not been previously characterized before the Dubna experiments, a situation which the JWP generally considers "troublesome, but not necessarily exclusive".

§RIKEN

On July 23, 2004, a team of Japanese scientists at RIKEN bombarded a target of bismuth-209 with accelerated nuclei of zinc-70 and detected a single atom of the isotope ununtrium-278. They published their results on September 28, 2004:

209
83Bi + 70
30Zn â†' 278
113Uut + 1
0n

Previously, in 2000, a team led by P. A. Wilk identified the decay product ²⁶⁶Bh as decaying with identical properties to what the Japanese team had observed, thus lending support for their claim. However, they also observed the daughter of ²⁶⁶Bh, ²⁶²Db, undergo alpha decay instead of spontaneous fission (the Japanese team observed the latter decay mode).

The RIKEN team produced a further atom on April 2, 2005, although the decay data were slightly different from the first chain, perhaps due to either the formation of a metastable state or an alpha particle escaping from the detector before depositing its full energy. Due to these inconsistencies in the decay data, the small number of ununtrium atoms produced, and the lack of unambiguous anchors to known isotopes, the JWP did not accept this as a conclusive discovery of ununtrium in 2011.

Most recently, production and identification of another ²⁷⁸Uut nucleus occurred at RIKEN on August 12, 2012. In this case, a series of six alpha decays was observed, leading down to an isotope of mendelevium:

278
113Uut â†' 274
111Rg + α â†' 270
109Mt + α â†' 266
107Bh + α â†' 262
105Db + α â†' 258
103Lr + α â†' 254
101Md + α

This decay chain differed from the previous observations at RIKEN mainly in the decay mode of dubnium, which was previously observed to undergo spontaneous fission, but in this case instead alpha decayed. Because the alpha decay of dubnium-262 to lawrencium-258 is well known, this provides unambiguous proof that element 113 is the origin of the chain. The scientists on this team calculated the probability of accidental coincidence to be 10^âˆ'28, or totally negligible.

§Naming

Ununtrium is the lightest element that has not yet received an official name. Using Mendeleev's nomenclature for unnamed and undiscovered elements, ununtrium should be known as eka-thallium or dvi-indium. In 1979 IUPAC published recommendations according to which the element was to be called ununtrium (with the corresponding symbol of Uut), a systematic element name as a placeholder, until the discovery of the element is confirmed and a name is decided on. The recommendations are largely ignored among scientists, who call it "element 113", with the symbol of (113) or even simply 113.

Claims to the discovery of ununtrium have been put forward by both the Dubna and RIKEN teams. The IUPAC/IUPAP Joint Working Party (JWP) will decide to whom the right to suggest a name will be given. In 2011, the IUPAC evaluated the 2004 RIKEN experiments and 2004 and 2007 Dubna experiments, and concluded that they did not meet the criteria for discovery. Another evaluation of more recent experiments will take place within the next few years.

On August 12, 2012, researchers at the RIKEN Nishina Center for Accelerator-Based Science in Japan, claimed to have synthesised element 113 by colliding zinc nuclei (with 30 protons each) into a thin layer of bismuth (which contains 83 protons). If the discovery gets approved by the IUPAC/IUPAP Joint Working Party (JWP), this will be the first time in history that a team of Asian physicists will get to name a new element.

The following names have been suggested by the above-mentioned teams claiming discovery:

§Isotopes

Ununtrium has no stable or naturally-occurring isotopes. Several radioactive isotopes have been synthesized in the laboratory, either by fusing two atoms or by observing the decay of heavier elements. Six different isotopes of ununtrium have been reported with atomic masses 278 and 282â€"286; they all decay through alpha decay.

§Stability and half-lives

All ununtrium isotopes are extremely unstable and radioactive; however, the heavier ununtrium isotopes are more stable than the lighter. The most stable known ununtrium isotope, ²⁸⁶Uut, is also the heaviest known ununtrium isotope; it has a half-life of 20 seconds. The isotope ²⁸⁵Uut has been reported to also have a half-life of over a second. The isotopes ²⁸⁴Uut and ²⁸³Uut have half-lives of 0.48 and 0.10 seconds respectively. The remaining two isotopes have half-lives between 0.1 and 100 milliseconds: ²⁸²Uut has a half-life of 70 milliseconds, and ²⁷⁸Uut, the lightest known ununtrium isotope, is also the shortest-lived known ununtrium isotope, with a half-life of just 0.24 milliseconds. It is predicted that even heavier undiscovered ununtrium isotopes could be much more stable: for example, ²⁸⁷Uut is predicted to have a half-life of around 20 minutes, close to two orders of magnitude more than that of ²⁸⁶Uut.

Theoretical estimates of alpha decay half-lives of isotopes of ununtrium are in good agreement with the experimental data. The undiscovered isotope ²⁹³Uut has been predicted to be the most stable towards beta decay; however, no known ununtrium isotope has been observed to undergo beta decay.

The stability of nuclei decreases greatly with the increase in atomic number after plutonium, the heaviest primordial element, so that all isotopes with an atomic number above 101 decay radioactively with a half-life under a day, with the exception of dubnium-268. Nevertheless, because of reasons not very well understood yet, there is a slight increased nuclear stability around atomic numbers 110â€"114, which leads to the appearance of what is known in nuclear physics as the "island of stability". This concept, proposed by University of California professor Glenn Seaborg, explains why superheavy elements last longer than predicted.

§Predicted properties

Ununtrium is the first member of the 7p series of elements and the heaviest boron group element on the periodic table, below boron, aluminium, gallium, indium, and thallium. It is predicted to show many differences from its lighter homologues: a largely contributing effect is the spinâ€"orbit (SO) interaction. It is especially strong for the superheavy elements, because their electrons move much faster than in lighter atoms, at velocities comparable to the speed of light. In relation to ununtrium atoms, it lowers the 7s and the 7p electron energy levels (stabilizing the corresponding electrons), but two of the 7p electron energy levels are stabilized more than the other four. The stabilization of the 7s electrons is called the inert pair effect, and the effect "tearing" the 7p subshell into the more stabilized and the less stabilized parts is called the subshell splitting. Computation chemists see the split as a change of the second (azimuthal) quantum number l from 1 to 1/2 and 3/2 for the more stabilized and less stabilized parts of the 7p subshell, respectively. For many theoretical purposes, the valence electron configuration may be represented to reflect the 7p subshell split as 7s²7p_1/2¹. These effects stabilize lower oxidation states: the first ionization energy of ununtrium is expected to be 7.306 eV, the highest among the boron group elements. Hence, the most stable oxidation state of ununtrium is predicted to be the +1 state, and ununtrium is expected to be less reactive than thallium. Differences for other electron levels also exist. For example, the 6d electron levels (also split in halves, with four being 6d_3/2 and six being 6d_5/2) are both raised, so that they are close in energy to the 7s ones. Thus, the 6d electron levels, being destabilized, should still be able to participate in chemical reactions in ununtrium (as well as in the next 7p element, flerovium), thus making it behave in some ways like transition metals and allow higher oxidation states. Ununtrium should hence also be able to show stable +2, +3 and +5 oxidation states. However, the +3 state should still be less stable than the +1 state, following periodic trends. Ununtrium should be the most electronegative among all the boron group elements: for example, in the compound UutUus, the negative charge is expected to be on the ununtrium atom rather than the ununseptium atom, the opposite of what would be expected from simple periodicity. The electron affinity of ununtrium is calculated to be around 0.68 eV; in comparison, that of thallium is 0.4 eV. The high electron affinity and electronegativity of ununtrium are due to it being only one electron short of the closed-shell valence electron configuration of flerovium (7s²7p_1/2²): this would make the âˆ'1 oxidation state of ununtrium more stable than that of its lighter congener thallium.

The simplest possible ununtrium compound is the monohydride, UutH. The bonding is provided by the 7p_1/2 electron of ununtrium and the 1s electron of hydrogen. However, the SO interaction causes the binding energy of ununtrium monohydride to be reduced by about 1 eV and the ununtriumâ€"hydrogen bond length to decrease as the bonding 7p_1/2 orbital is relativistically contracted. The analogous monofluoride (UutF) should also exist. Ununtrium should also be able to form the trihydride (UutH₃), trifluoride (UutF₃), and trichloride (UutCl₃), with ununtrium in the +3 oxidation state. Because the 6d electrons are involved in bonding instead of the 7s ones, these molecules are predicted to be T-shaped and not trigonal planar. Although the polyfluoride anion UutFâˆ'
6 should be stable, the corresponding neutral fluoride UutF₅ should be unstable, spontaneously decomposing into the trifluoride and elemental fluorine. Ununtrium(I) is predicted to be more similar to silver(I) than thallium(I): the Uut⁺ ion is expected to more willingly bind anions, so that UutCl should be quite soluble in an excess of hydrochloric acid or in ammonia while TlCl is not. Additionally, in contrast to the strongly basic TlOH, ununtrium(I) should instead form Uut₂O, which would be weakly water-soluble and readily ammonia-soluble.

Ununtrium is expected to be much denser than thallium, having a predicted density of about 16 to 18 g/cm³, due to the relativistic stabilization and contraction of its 7s and 7p_1/2 orbitals. This is because calculations estimate it to have an atomic radius of about 170 pm, the same as that of thallium, even though periodic trends would predict it to have an atomic radius larger than that of thallium due to it being one period further down in the periodic table. The melting and boiling points of ununtrium are not definitely known, but have been calculated to be 430 °C and 1100 °C respectively, exceeding the values for gallium, indium, and thallium, following periodic trends.

§Experimental chemistry

Unambiguous determination of the chemical characteristics of ununtrium has yet to have been established. The isotopes ²⁸⁴Uut, ²⁸⁵Uut, and ²⁸⁶Uut have half-lives long enough for chemical investigation. It is theoretically predicted that ununtrium should have an enthalpy of sublimation around 150 kJ/mol and an enthalpy of adsorption on a gold surface around âˆ'159 kJ/mol. From 2010 to 2012, some preliminary chemical experiments were performed to determine the volatility of ununtrium. The reaction used was ²⁴³Am(⁴⁸Ca,3n)²⁸⁸Uup; the isotope ²⁸⁸Uup has a short half-life and would quickly decay to the longer-lived ²⁸⁴Uut, which would be chemically investigated. Teflon capillaries at 70 °C connecting the recoil chamber, where the ununtrium atoms were synthesized, and the gold-covered detectors: the ununtrium atoms would be carried along the capillaries by a carrier gas. While about ten to twenty atoms of ²⁸⁴Uut were produced, none of these atoms were registerd by the gold-covered detectors, suggesting either that ununtrium was similar in volatility to the noble gases or, more plausibly, that pure ununtrium was not very volatile and thus could not efficiently pass through the Teflon capillaries at 70 °C. Formation of the hydroxide UutOH would ease the transport, as UutOH is expected to be more volatile than elemental ununtrium, and this reaction could be facilitated by adding more water vapor into the carrier gas. However, it seems likely that this formation is not kinetically favored, so that one would need to use the longer-lived isotope ²⁸⁶Uut in future experiments.

§See also

• Isotopes of ununtrium
• Island of stability

§Notes

§References

§External links

• Ununtrium at The Periodic Table of Videos (University of Nottingham)
• Uut and Uup Add Their Atomic Mass to Periodic Table
• Apsidium: Ununtrium 113 Uut
• Discovery of Elements 113 and 115
• Superheavy elements
• WebElements.com: Ununtrium

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