Московий: синтетический радиоактивный элемент 115

Moscovium is a synthetic chemical element; it has symbol Mc and atomic number 115. It was first synthesized in 2003 by a joint team of Russian and American scientists at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. In December 2015, it was recognized as one of four new elements by the Joint Working Party of international scientific bodies IUPAC and IUPAP. On 28 November 2016, it was officially named after the Moscow Oblast, in which the JINR is situated. Moscovium is an extremely radioactive element: its most stable known isotope, moscovium 290, has a half life of only 0.65 seconds. In the periodic table, it is a p block transactinide element. It is a member of the 7th period and is placed in group 15 as the heaviest pnictogen, although it has not been confirmed to behave as a heavier homologue of the pnictogen bismuth. Moscovium is calculated to have some properties similar to its lighter homologues, nitrogen, phosphorus, arsenic, antimony, and bismuth, and to be a post transition metal, although it should also show several major differences from them. In particular, moscovium should also have significant similarities to thallium, as both have one rather loosely bound electron outside a quasi closed shell. Over a hundred atoms of moscovium have been observed to date, all of which have been shown to have mass numbers from 286 to 290.

Superheavy element

The first successful synthesis of moscovium was by a joint team of Russian and American scientists in August 2003 at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. Headed by Russian nuclear physicist Yuri Oganessian, the team included American scientists of the Lawrence Livermore National Laboratory. The researchers on February 2, 2004, stated in Physical Review C that they bombarded americium 243 with calcium 48 ions to produce four atoms of moscovium. These atoms decayed by emission of alpha particles to nihonium in about 100 milliseconds. The Dubna–Livermore collaboration strengthened their claim to the discoveries of moscovium and nihonium by conducting chemical experiments on the final decay product 268Db. None of the nuclides in this decay chain were previously known, so existing experimental data was not available to support their claim. In June 2004 and December 2005, the presence of a dubnium isotope was confirmed 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). However, 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 the chemical properties of group 4 and group 5 elements with sufficient confidence. Furthermore, the decay properties of all the nuclei in the decay chain of moscovium had not been previously characterized before the Dubna experiments, a situation which the JWP generally considers "troublesome, but not necessarily exclusive". Simultaneously, the 2004 experiment had been repeated at Dubna, now additionally also creating the isotope 289Mc that could serve as a cross bombardment for confirming the discovery of the tennessine isotope 293Ts in 2010. In December 2015, the IUPAC/IUPAP Joint Working Party recognized the element's discovery and assigned the priority to the Dubna Livermore collaboration of 2009–2010, giving them the right to suggest a permanent name for it. While they did not recognise the experiments synthesising 287Mc and 288Mc as persuasive due to the lack of a convincing identification of atomic number via cross reactions, they recognised the 293Ts experiments as persuasive because its daughter 289Mc had been produced independently and found to exhibit the same properties. In May 2016, Lund University (Lund, Scania, Sweden) and GSI cast some doubt on the syntheses of moscovium and tennessine. The decay chains assigned to 289Mc, the isotope instrumental in the confirmation of the syntheses of moscovium and tennessine, were found based on a new statistical method to be too different to belong to the same nuclide with a reasonably high probability. The reported 293Ts decay chains approved as such by the JWP were found to require splitting into individual data sets assigned to different tennessine isotopes. It was also found that the claimed link between the decay chains reported as from 293Ts and 289Mc probably did not exist. (On the other hand, the chains from the non approved isotope 294Ts were found to be congruent.) The multiplicity of states found when nuclides that are not even–even undergo alpha decay is not unexpected and contributes to the lack of clarity in the cross reactions. This study criticized the JWP report for overlooking subtleties associated with this issue, and considered it "problematic" that the only argument for the acceptance of the discoveries of moscovium and tennessine was a link they considered to be doubtful. On June 8, 2017, two members of the Dubna team published a journal article answering these criticisms, analysing their data on the nuclides 293Ts and 289Mc with widely accepted statistical methods, noted that the 2016 studies indicating non congruence produced problematic results when applied to radioactive decay: they excluded from the 90% confidence interval both average and extreme decay times, and the decay chains that would be excluded from the 90% confidence interval they chose were more probable to be observed than those that would be included. The 2017 reanalysis concluded that the observed decay chains of 293Ts and 289Mc were consistent with the assumption that only one nuclide was present at each step of the chain, although it would be desirable to be able to directly measure the mass number of the originating nucleus of each chain as well as the excitation function of the 243Am+48Ca reaction.

Using Mendeleev's nomenclature for unnamed and undiscovered elements, moscovium is sometimes known as eka bismuth. In 1979, IUPAC recommended that the placeholder systematic element name ununpentium (with the corresponding symbol of Uup) be used until the discovery of the element is confirmed and a permanent name is decided. Although widely used in the chemical community on all levels, from chemistry classrooms to advanced textbooks, the recommendations were mostly ignored among scientists in the field, who called it "element 115", with the symbol of E115, (115) or even simply 115. According to IUPAC recommendations, the discoverer(s) of a new element has the right to suggest a name. A suggested name was langevinium, after Paul Langevin. Later, the Dubna team mentioned the name moscovium several times as one among many possibilities, referring to the Moscow Oblast where Dubna is located. In June 2016, IUPAC endorsed the latter proposal to be formally accepted by the end of the year, which it was on 28 November 2016.

Other than nuclear properties, no properties of moscovium or its compounds have been measured; this is due to its extremely limited and expensive production and the fact that it decays very quickly. Properties of moscovium remain unknown and only predictions are available.

Moscovium is expected to be within an island of stability centered on copernicium (element 112) and flerovium (element 114). Due to the expected high fission barriers, any nucleus within this island of stability exclusively decays by alpha decay and perhaps some electron capture and beta decay. Although the known isotopes of moscovium do not actually have enough neutrons to be on the island of stability, they can be seen to approach the island as in general, the heavier isotopes are the longer lived ones. Other possibilities to synthesize nuclei on the island of stability include quasifission (partial fusion followed by fission) of a massive nucleus. Recently it has been shown that the multi nucleon transfer reactions in collisions of actinide nuclei (such as uranium and curium) might be used to synthesize the neutron rich superheavy nuclei located at the island of stability, although formation of the lighter elements nobelium or seaborgium is more favored. 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 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.

Moscovium is predicted to be the third member of the 7p series of chemical elements and the heaviest member of group 15 in the periodic table, below bismuth. Unlike the two previous 7p elements, moscovium is expected to be a good homologue of its lighter congener, in this case bismuth. In this group, each member is known to portray the group oxidation state of +5 but with differing stability. For nitrogen, the +5 state is mostly a formal explanation of molecules like N2O5: it is very difficult to have five covalent bonds to nitrogen due to the inability of the small nitrogen atom to accommodate five ligands. The +5 state is well represented for the essentially non relativistic typical pnictogens phosphorus, arsenic, and antimony. However, for bismuth it becomes rare due to the relativistic stabilization of the 6s orbitals known as the inert pair effect, so that the 6s electrons are reluctant to bond chemically. It is expected that moscovium will have an inert pair effect for both the 7s and the 7p1/2 electrons, as the binding energy of the lone 7p3/2 electron is noticeably lower than that of the 7p1/2 electrons. Nitrogen(I) and bismuth(I) are known but rare and moscovium(I) is likely to show some unique properties, probably behaving more like thallium(I) than bismuth(I). Because of spin orbit coupling, flerovium may display closed shell or noble gas like properties; if this is the case, moscovium will likely be typically monovalent as a result, since the cation Mc+ will have the same electron configuration as flerovium, perhaps giving moscovium some alkali metal character. Calculations predict that moscovium(I) fluoride and chloride would be ionic compounds, with an ionic radius of about 109–114 pm for Mc+, although the 7p1/2 lone pair on the Mc+ ion should be highly polarisable. The Mc3+ cation should behave like its true lighter homolog Bi3+. The 7s electrons are too stabilized to be able to contribute chemically and hence the +5 state should be impossible and moscovium may be considered to have only three valence electrons. Moscovium would be quite a reactive metal, with a standard reduction potential of −1.5 V for the Mc+/Mc couple. The chemistry of moscovium in aqueous solution should essentially be that of the Mc+ and Mc3+ ions. The former should be easily hydrolyzed and not be easily complexed with halides, cyanide, and ammonia. Moscovium(I) hydroxide (McOH), carbonate (Mc2CO3), oxalate (Mc2C2O4), and fluoride (McF) should be soluble in water; the sulfide (Mc2S) should be insoluble; and the chloride (McCl), bromide (McBr), iodide (McI), and thiocyanate (McSCN) should be only slightly soluble, so that adding excess hydrochloric acid would not noticeably affect the solubility of moscovium(I) chloride. Mc3+ should be about as stable as Tl3+ and hence should also be an important part of moscovium chemistry, although its closest homolog among the elements should be its lighter congener Bi3+. Moscovium(III) fluoride (McF3) and thiozonide (McS3) should be insoluble in water, similar to the corresponding bismuth compounds, while moscovium(III) chloride (McCl3), bromide (McBr3), and iodide (McI3) should be readily soluble and easily hydrolyzed to form oxyhalides such as McOCl and McOBr, again analogous to bismuth. Both moscovium(I) and moscovium(III) should be common oxidation states and their relative stability should depend greatly on what they are complexed with and the likelihood of hydrolysis. Like its lighter homologues ammonia, phosphine, arsine, stibine, and bismuthine, moscovine (McH3) is expected to have a trigonal pyramidal molecular geometry, with an Mc–H bond length of 195.4 pm and a H–Mc–H bond angle of 91.8° (bismuthine has bond length 181.7 pm and bond angle 91.9°; stibine has bond length 172.3 pm and bond angle 92.0°). In the predicted aromatic pentagonal planar Mc5 cluster, analogous to pentazolate (N5 ), the Mc–Mc bond length is expected to be expanded from the extrapolated value of 156–158 pm to 329 pm due to spin–orbit coupling effects.

Unambiguous determination of the chemical characteristics of moscovium has yet to have been established. In 2011, experiments were conducted to create nihonium, flerovium, and moscovium isotopes in the reactions between calcium 48 projectiles and targets of americium 243 and plutonium 244. However, the targets included lead and bismuth impurities and hence some isotopes of bismuth and polonium were generated in nucleon transfer reactions. This, while an unforeseen complication, could give information that would help in the future chemical investigation of the heavier homologs of bismuth and polonium, which are respectively moscovium and livermorium.