Теннессин: Жаңа элементтің ашылу тарихы

Tennessine is a synthetic chemical element; it has symbol Ts and atomic number 117. It has the second highest atomic number and joint highest atomic mass of all known elements, and is the penultimate element of the 7th period of the periodic table. The discovery of tennessine was officially announced in Dubna, Russia, by a Russian–American collaboration in April 2010, which makes it the most recently discovered element as of 2024. One of its daughter isotopes was created directly in 2011, partially confirming the results of the experiment. The experiment itself was repeated successfully by the same collaboration in 2012 and by a joint German–American team in May 2014. In December 2015, the Joint Working Party of the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP), which evaluates claims of discovery of new elements, recognized the element and assigned the priority to the Russian–American team. In June 2016, the IUPAC published a declaration stating that the discoverers had suggested the name tennessine after Tennessee, United States, a name which was officially adopted in November 2016. Tennessine may be located in the "island of stability", a concept that explains why some superheavy elements are more stable compared to an overall trend of decreasing stability for elements beyond bismuth on the periodic table. The synthesized tennessine atoms have lasted tens and hundreds of milliseconds. In the periodic table, tennessine is expected to be a member of group 17, the halogens. Of the aimed for 117 protons, calcium has 20, and thus they needed to use berkelium, which has 97 protons in its nucleus. In February 2005, the leader of the JINR team — Yuri Oganessian — presented a colloquium at ORNL. Also in attendance were representatives of Lawrence Livermore National Laboratory, who had previously worked with JINR on the discovery of elements 113–116 and 118, and Joseph Hamilton of Vanderbilt University, a collaborator of Oganessian.

ORNL resumed californium production in spring 2008. Hamilton noted the restart during the summer and made a deal on subsequent extraction of berkelium (the price was about $600,000). During a September 2008 symposium at Vanderbilt University in Nashville, Tennessee, celebrating his 50th year on the Physics faculty, Hamilton introduced Oganessian to James Roberto (then the deputy director for science and technology at ORNL). They established a collaboration among JINR, ORNL, and Vanderbilt. this is particularly notable as because of it the IUPAC recognizes her as the first African American woman to be involved with the discovery of a chemical element. The eventual collaborating institutions also included The University of Tennessee (Knoxville), Lawrence Livermore National Laboratory, The Research Institute for Advanced Reactors (Russia), and The University of Nevada (Las Vegas). In November 2008, the U. S. Department of Energy, which had oversight over the reactor in Oak Ridge, allowed the scientific use of the extracted berkelium. The production lasted 250 days and ended in late December 2008, The target was packed into five lead containers to be flown from New York to Moscow. In July 2009, it was transported to Dubna, The calcium 48 beam was generated by chemically extracting the small quantities of calcium 48 present in naturally occurring calcium, enriching it 500 times. This work was done in the closed town of Lesnoy, Sverdlovsk Oblast, Russia. The obtained data from the experiment was sent to the LLNL for further analysis. On 9 April 2010, an official report was released in the journal Physical Review Letters identifying the isotopes as 294117 and 293117, which were shown to have half lives on the order of tens or hundreds of milliseconds. The work was signed by all parties involved in the experiment to some extent: JINR, ORNL, LLNL, RIAR, Vanderbilt, the University of Tennessee (Knoxville, Tennessee, U. S.), and the University of Nevada (Las Vegas, Nevada, U. S.), which provided data analysis support. The isotopes were formed as follows: therefore, their properties could not be used to confirm the claim of discovery. In 2011, when one of the decay products (115) was synthesized directly, its properties matched those measured in the claimed indirect synthesis from the decay of element 117. The discoverers did not submit a claim for their findings in 2007–2011 when the Joint Working Party was reviewing claims of discoveries of new elements. The Dubna team repeated the experiment in 2012, creating seven atoms of element 117 and confirming their earlier synthesis of element 118 (produced after some time when a significant quantity of the berkelium 249 target had beta decayed to californium 249). The results of the experiment matched the previous outcome; The team repeated the Dubna experiment using the Darmstadt accelerator, creating two atoms of element 117. and thus the listed discoverers — JINR, LLNL, and ORNL — were given the right to suggest an official name for the element. (Vanderbilt was left off the initial list of discoverers in an error that was later corrected.) In May 2016, Lund University (Lund, Scania, Sweden) and GSI cast some doubt on the syntheses of elements 115 and 117. The decay chains assigned to 115, the isotope instrumental in the confirmation of the syntheses of elements 115 and 117, 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 293117 decay chains approved as such by the JWP were found to require splitting into individual data sets assigned to different isotopes of element 117. It was also found that the claimed link between the decay chains reported as from 117 and 115 probably did not exist. (On the other hand, the chains from the non approved isotope 117 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 elements 115 and 117 was a link they considered to be doubtful. On 8 June 2017, two members of the Dubna team published a journal article answering these criticisms, analysing their data on the nuclides 117 and 115 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 117 and 115 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 reaction.

Using Mendeleev's nomenclature for unnamed and undiscovered elements, element 117 should be known as eka astatine. Using the 1979 recommendations by the International Union of Pure and Applied Chemistry (IUPAC), the element was temporarily called ununseptium (symbol Uus), formed from Latin roots "one", "one", and "seven", a reference to the element's atomic number 117. Many scientists in the field called it "element 117", with the symbol E117, (117), or 117. however, the new recommendations published in 2016 recommended using the " ine" ending for all new group 17 elements. After the original synthesis in 2010, Dawn Shaughnessy of LLNL and Oganessian declared that naming was a sensitive question, and it was avoided as far as possible. However, Hamilton declared that year, "I was crucial in getting the group together and in getting the 249Bk target essential for the discovery. As a result of that, I'm going to get to name the element. I can't tell you the name, but it will bring distinction to the region." In March 2016, the discovery team agreed on a conference call involving representatives from the parties involved on the name "tennessine" for element 117. In November 2016, the names, including tennessine, were formally accepted. Concerns that the proposed symbol Ts may clash with a notation for the tosyl group used in organic chemistry were rejected, following existing symbols bearing such dual meanings: Ac (actinium and acetyl) and Pr (praseodymium and propyl). The naming ceremony for moscovium, tennessine, and oganesson was held on 2 March 2017 at the Russian Academy of Sciences in Moscow; a separate ceremony for tennessine alone had been held at ORNL in January 2017.

Other than nuclear properties, no properties of tennessine or its compounds have been measured; this is due to its extremely limited and expensive production This is because of the ever increasing Coulomb repulsion of protons, so that the strong nuclear force cannot hold the nucleus together against spontaneous fission for long. Calculations suggest that in the absence of other stabilizing factors, elements with more than 104 protons should not exist. However, researchers in the 1960s suggested that the closed nuclear shells around 114 protons and 184 neutrons should counteract this instability, creating an "island of stability" where nuclides could have half lives reaching thousands or millions of years. While scientists have still not reached the island, the mere existence of the superheavy elements (including tennessine) confirms that this stabilizing effect is real, and in general the known superheavy nuclides become exponentially longer lived as they approach the predicted location of the island. Tennessine is the second heaviest element created so far, and all its known isotopes have half lives of less than one second. Nevertheless, this is longer than the values predicted prior to their discovery: the predicted lifetimes for 293Ts and 294Ts used in the discovery paper were 10 ms and 45 ms respectively, while the observed lifetimes were 21 ms and 112 ms respectively.]] It has been calculated that the isotope 295Ts would have a half life of about 18 milliseconds, and it may be possible to produce this isotope via the same berkelium–calcium reaction used in the discoveries of the known isotopes, 293Ts and 294Ts. The chance of this reaction producing 295Ts is estimated to be, at most, one seventh the chance of producing 294Ts. Calculations using a quantum tunneling model predict the existence of several isotopes of tennessine up to 303Ts. The most stable of these is expected to be 296Ts with an alpha decay half life of 40 milliseconds. A liquid drop model study on the element's isotopes shows similar results; it suggests a general trend of increasing stability for isotopes heavier than 301Ts, with partial half lives exceeding the age of the universe for the heaviest isotopes like 335Ts when beta decay is not considered. Lighter isotopes of tennessine may be produced in the 243Am+50Ti reaction, which was considered as a contingency plan by the Dubna team in 2008 if 249Bk proved unavailable.

Tennessine is expected to be a member of group 17 in the periodic table, below the five halogens; fluorine, chlorine, bromine, iodine, and astatine, each of which has seven valence electrons with a configuration of ns2np5. For tennessine, being in the seventh period (row) of the periodic table, continuing the trend would predict a valence electron configuration of 7s27p5, As such, an extrapolation based on periodic trends would predict tennessine to be a rather volatile metal. Calculations have confirmed the accuracy of this simple extrapolation, although experimental verification of this is currently impossible as the half lives of the known tennessine isotopes are too short. The stabilization of the 7s electrons is called the inert pair effect; the effect that separates the 7p subshell into the more stabilized and the less stabilized parts is called subshell splitting. Computational chemists understand 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 With the seven outermost electrons removed, tennessine is finally smaller; 57 pm These values exceed those of astatine and the lighter halogens, following periodic trends. A later paper predicts the boiling point of tennessine to be 345 °C (that of astatine is estimated as 309 °C, 337 °C, or 370 °C, although experimental values of 230 °C and 411 °C have been reported). The density of tennessine is expected to be between 7.1 and 7.3 g/cm3. Unlike the lighter group 17 elements, tennessine may not exhibit the chemical behavior common to the halogens. For example, fluorine, chlorine, bromine, and iodine routinely accept an electron to achieve the more stable electronic configuration of a noble gas, obtaining eight electrons (octet) in their valence shells instead of seven. This ability weakens as atomic weight increases going down the group; tennessine would be the least willing group 17 element to accept an electron. Of the oxidation states it is predicted to form, −1 is expected to be the least common. Since the tennessine p electron bonds are two thirds sigma, the bond is only two thirds as strong as it would be if tennessine featured no spin–orbit interactions. the positive value implying that the negative charge is on the tennessine atom. For NhTs, the strength of the effects are predicted to cause a transfer of the electron from the tennessine atom to the nihonium atom, with the dipole moment value being −1.80 D. The spin–orbit interaction increases the dissociation energy of the TsF molecule because it lowers the electronegativity of tennessine, causing the bond with the extremely electronegative fluorine atom to have a more ionic character. The TsF3 molecule is predicted to be significantly stabilized by spin–orbit interactions; a possible rationale may be the large difference in electronegativity between tennessine and fluorine, giving the bond a partially ionic character.