Oganesson

Oganesson is a synthetic chemical element; it has symbol Og and atomic number 118. It was first synthesized in 2002 at the Joint Institute for Nuclear Research (JINR) in Dubna, near Moscow, Russia, by a joint team of Russian and American scientists. In December 2015, it was recognized as one of four new elements by the Joint Working Party of the international scientific bodies IUPAC and IUPAP. It was formally named on 28 November 2016. The name honors the nuclear physicist Yuri Oganessian, who played a leading role in the discovery of the heaviest elements in the periodic table.

Oganesson has the highest atomic number and highest atomic mass of all known elements. On the periodic table of the elements it is a p-block element, a member of group 18, and the last member of period 7. Its only known isotope, oganesson-294, is highly radioactive, with a half-life of 0.7 ms. This half-life is too short for chemical studies. Because of relativistic effects, theoretical studies predict that it would be a solid at room temperature, and significantly reactive, Following this, German chemist Aristid von Grosse wrote an article in 1965 predicting the likely properties of element 118.

Unconfirmed discovery claims

In late 1998, Polish physicist Robert Smolańczuk published calculations on the fusion of atomic nuclei towards the synthesis of superheavy atoms, including oganesson. His calculations suggested that it might be possible to make element 118 by fusing lead with krypton under carefully controlled conditions, and that the fusion probability (cross section) of that reaction would be close to the lead–chromium reaction that had produced element 106, seaborgium. This contradicted predictions that the cross sections for reactions with lead or bismuth targets would go down exponentially as the atomic number of the resulting elements increased. and very soon after the results were reported in Science. The researchers reported that they had performed the reaction

In 2001, they published a retraction after researchers at other laboratories were unable to duplicate the results and the Berkeley lab could not duplicate them either. 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 principal author Victor Ninov. Newer experimental results and theoretical predictions have confirmed the exponential decrease in cross sections with lead and bismuth targets as the atomic number of the resulting nuclide increases.

Discovery reports

thumb|upright=0.9|alt=Schematic diagram of oganesson-294 alpha decay, with a half-life of 0.89 ms and a decay energy of 11.65 MeV. The resulting livermorium-290 decays by alpha decay, with a half-life of 10.0 ms and a decay energy of 10.80 MeV, to flerovium-286. Flerovium-286 has a half-life of 0.16 s and a decay energy of 10.16 MeV, and undergoes alpha decay to copernicium-282 with a 0.7 rate of spontaneous fission. Copernicium-282 itself has a half-life of only 1.9 ms and has a 1.0 rate of spontaneous fission.|[[Radioactive decay pathway of the isotope oganesson-294. The discovery was not announced immediately, because the decay energy of 294Og matched that of 212mPo, a common impurity produced in fusion reactions aimed at producing superheavy elements, and thus announcement was delayed until after a 2005 confirmatory experiment aimed at producing more oganesson atoms. and two more in 2005) produced via collisions of californium-249 atoms and calcium-48 ions.

In 2011, IUPAC evaluated the 2006 results of the Dubna–Livermore collaboration and concluded: "The three events reported for the Z = 118 isotope have very good internal

redundancy but with no anchor to known nuclei do not satisfy the criteria for discovery".

Because of the very small fusion reaction probability (the fusion cross section is or ) the experiment took four months and involved a beam dose of calcium ions that had to be shot at the californium target to produce the first recorded event believed to be the synthesis of oganesson. Nevertheless, researchers were highly confident that the results were not a false positive, since the chance that the detections were random events was estimated to be less than one part in .

In the experiments, the alpha-decay of three atoms of oganesson was observed. A fourth decay by direct spontaneous fission was also proposed. A half-life of 0.89 ms was calculated: decays into by alpha decay. Since there were only three nuclei, the half-life derived from observed lifetimes has a large uncertainty: . This was on account of two 2009 and 2010 confirmations of the properties of the granddaughter of 294Og, 286Fl, at the Lawrence Berkeley National Laboratory, as well as the observation of another consistent decay chain of 294Og by the Dubna group in 2012. The goal of that experiment had been the synthesis of 294Ts via the reaction 249Bk(48Ca,3n), but the short half-life of 249Bk resulted in a significant quantity of the target having decayed to 249Cf, resulting in the synthesis of oganesson instead of tennessine.

From 1 October 2015 to 6 April 2016, the Dubna team performed a similar experiment with 48Ca projectiles aimed at a mixed-isotope californium target containing 249Cf, 250Cf, and 251Cf, with the aim of producing the heavier oganesson isotopes 295Og and 296Og. Two beam energies at 252 MeV and 258 MeV were used. Only one atom was seen at the lower beam energy, whose decay chain fitted the previously known one of 294Og (terminating with spontaneous fission of 286Fl), and none were seen at the higher beam energy. The experiment was then halted, as the glue from the sector frames covered the target and blocked evaporation residues from escaping to the detectors. The production of 293Og and its daughter 289Lv, as well as the even heavier isotope 297Og, is also possible using this reaction. The isotopes 295Og and 296Og may also be produced in the fusion of 248Cm with 50Ti projectiles. These heavier and likely more stable isotopes may be useful in probing the chemistry of oganesson. A search in 2017 at RIKEN using this reaction was unsuccessful.

Naming

thumb|right|upright=1.1|Element 118 was named after [[Yuri Oganessian, a pioneer in the discovery of synthetic elements, with the name oganesson (Og). Oganessian and the decay chain of oganesson-294 were pictured on a stamp of Armenia issued on 28 December 2017.]]

Using Mendeleev's nomenclature for unnamed and undiscovered elements, oganesson is sometimes known as eka-radon (until the 1960s as eka-emanation, emanation being the old name for radon). and recommended that it be used until after confirmed discovery of the element. 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 118", with the symbol of E118, (118), or simply 118.

The Russian discoverers reported their synthesis in 2006. According to IUPAC recommendations, the discoverers of a new element have the right to suggest a name. In 2007, the head of the Russian institute stated the team were considering two names for the new element: flyorium, in honor of Georgy Flyorov, the founder of the research laboratory in Dubna; and moskovium, in recognition of the Moscow Oblast where Dubna is located. He also stated that although the element was discovered as an American collaboration, who provided the californium target, the element should rightly be named in honor of Russia since the Flyorov Laboratory of Nuclear Reactions at JINR was the only facility in the world which could achieve this result. These names were later suggested for element 114 (flerovium) and element 116 (moscovium). Flerovium became the name of element 114; the final name proposed for element 116 was instead livermorium, with moscovium later being proposed and accepted for element 115 instead. While the provisional name ununoctium followed this convention, a new IUPAC recommendation published in 2016 recommended using the "-on" ending for new group 18 elements, regardless of whether they turn out to have the chemical properties of a noble gas.

The scientists involved in the discovery of element 118, as well as those of 117 and 115, held a conference call on 23 March 2016 to decide their names. Element 118 was the last to be decided upon; after Oganessian was asked to leave the call, the remaining scientists unanimously decided to have the element "oganesson" after him. Oganessian was a pioneer in superheavy element research for sixty years reaching back to the field's foundation: his team and his proposed techniques had led directly to the synthesis of elements 107 through 118. Mark Stoyer, a nuclear chemist at the LLNL, later recalled, "We had intended to propose that name from Livermore, and things kind of got proposed at the same time from multiple places. I don't know if we can claim that we actually proposed the name, but we had intended it."

In internal discussions, IUPAC asked the JINR if they wanted the element to be spelled "oganeson" to match the Russian spelling more closely. Oganessian and the JINR refused this offer, citing the Soviet-era practice of transliterating names into the Latin alphabet under the rules of the French language ("Oganessian" is such a transliteration) and arguing that "oganesson" would be easier to link to the person. In 2017, Oganessian commented on the naming:|Yuri Oganessian

The naming ceremony for moscovium, tennessine, and oganesson was held on 2 March 2017 at the Russian Academy of Sciences in Moscow.

In a 2019 interview, when asked what it was like to see his name in the periodic table next to Einstein, Mendeleev, the Curies, and Rutherford, Oganessian responded:

Characteristics

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

Nuclear stability and isotopes

thumb|upright=1.5|Oganesson (row 118) is slightly above the "[[island of stability" (white ellipse) and thus its nuclei are slightly more stable than otherwise predicted.]]

The stability of nuclei quickly decreases with the increase in atomic number after curium, element 96, whose most stable isotope, 247Cm, has a half-life four orders of magnitude longer than that of any subsequent element. All nuclides with an atomic number above 101 undergo radioactive decay with half-lives shorter than 30 hours. No elements with atomic numbers above 82 (after lead) have stable isotopes. 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 in which 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 oganesson) 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. Oganesson is radioactive, decaying via alpha decay and spontaneous fission, with a half-life that appears to be less than a millisecond. Nonetheless, this is still longer than some predicted values.

Calculations using a quantum-tunneling model predict the existence of several heavier isotopes of oganesson with alpha-decay half-lives close to 1 ms.

Theoretical calculations done on the synthetic pathways for, and the half-life of, other isotopes have shown that some could be slightly more stable than the synthesized isotope 294Og, most likely 293Og, 295Og, 296Og, 297Og, 298Og, 300Og and 302Og (the last reaching the N = 184 shell closure). Of these, 297Og might provide the best chances for obtaining longer-lived nuclei, The isotopes from 291Og to 295Og might be produced as daughters of element 120 isotopes that can be reached in the reactions 249–251Cf+50Ti, 245Cm+48Ca, and 248Cm+48Ca.

In a quantum-tunneling model, the alpha decay half-life of was predicted to be Calculation with theoretical Q-values from the macroscopic-microscopic model of Muntian–Hofman–Patyk–Sobiczewski gives somewhat lower but comparable results.

Calculated atomic and physical properties

Oganesson is a member of group 18, the zero-valence elements. The members of this group are usually inert to most common chemical reactions (for example, combustion) because the outer valence shell is completely filled with eight electrons. This produces a stable, minimum energy configuration in which the outer electrons are tightly bound. It is thought that similarly, oganesson has a closed outer valence shell in which its valence electrons are arranged in a 7s27p6 configuration.

Following the periodic trend, oganesson would be expected to be slightly more reactive than radon. However, theoretical calculations have shown that it could be significantly more reactive. due to the relativistically stabilized 8s energy level and the destabilized 7p3/2 level, whereas copernicium and flerovium are predicted to have no electron affinity. Nevertheless, quantum electrodynamic corrections have been shown to be quite significant in reducing this affinity by decreasing the binding in the anion Og− by 9%, thus confirming the importance of these corrections in superheavy elements. Its second ionization energy should be around 1560 kJ/mol. Studies have also predicted that due to increasing electrostatic forces, oganesson may have a semibubble structure in proton density, having few protons at the center of its nucleus. Moreover, spin–orbit effects may cause bulk oganesson to be a semiconductor, with a band gap of  eV predicted. All the lighter noble gases are insulators instead: for example, the band gap of bulk radon is expected to be  eV.

Predicted compounds

right|upright=0.6|thumb|alt=Skeletal model of a terahedral molecule with a central atom (oganesson) symmetrically bonded to four peripheral (fluorine) atoms.| is predicted to have a tetrahedral molecular geometry.

The only confirmed isotope of oganesson, 294Og, has much too short a half-life to be chemically investigated experimentally. Therefore, no compounds of oganesson have been synthesized yet. Nevertheless, calculations on theoretical compounds have been performed since 1964. nevertheless, this appears not to be the case.

Calculations on the diatomic molecule showed a bonding interaction roughly equivalent to that calculated for , and a dissociation energy of 6 kJ/mol, roughly 4 times of that of . The +6 state would be less stable due to the strong binding of the 7p1/2 subshell. This is a result of the same spin–orbit interactions that make oganesson unusually reactive. For example, it was shown that the reaction of oganesson with to form the compound would release an energy of 106 kcal/mol of which about 46 kcal/mol come from these interactions. The Og–F bond will most probably be ionic rather than covalent, rendering the oganesson fluorides non-volatile. OgF2 is predicted to be partially ionic due to oganesson's high electropositivity. Oganesson is predicted to be sufficiently electropositive

Notes

References

Bibliography

External links

5 ways the heaviest element on the periodic table is really bizarre, ScienceNews.org
Element 118: Experiments on discovery, archive of discoverers' official web page
Element 118, Heaviest Ever, Reported for 1,000th of a Second, The New York Times.
It's Elemental: Oganesson
Oganesson at The Periodic Table of Videos (University of Nottingham)
On the Claims for Discovery of Elements 110, 111, 112, 114, 116, and 118 (IUPAC Technical Report)
WebElements: Oganesson