Oganesson

Oganesson, 118Og
Oganesson
Pronunciation
Mass number[294] (unconfirmed: 295)
Oganesson in the periodic table
HydrogenHelium
LithiumBerylliumBoronCarbonNitrogenOxygenFluorineNeon
SodiumMagnesiumAluminiumSiliconPhosphorusSulfurChlorineArgon
PotassiumCalciumScandiumTitaniumVanadiumChromiumManganeseIronCobaltNickelCopperZincGalliumGermaniumArsenicSeleniumBromineKrypton
RubidiumStrontiumYttriumZirconiumNiobiumMolybdenumTechnetiumRutheniumRhodiumPalladiumSilverCadmiumIndiumTinAntimonyTelluriumIodineXenon
CaesiumBariumLanthanumCeriumPraseodymiumNeodymiumPromethiumSamariumEuropiumGadoliniumTerbiumDysprosiumHolmiumErbiumThuliumYtterbiumLutetiumHafniumTantalumTungstenRheniumOsmiumIridiumPlatinumGoldMercury (element)ThalliumLeadBismuthPoloniumAstatineRadon
FranciumRadiumActiniumThoriumProtactiniumUraniumNeptuniumPlutoniumAmericiumCuriumBerkeliumCaliforniumEinsteiniumFermiumMendeleviumNobeliumLawrenciumRutherfordiumDubniumSeaborgiumBohriumHassiumMeitneriumDarmstadtiumRoentgeniumCoperniciumNihoniumFleroviumMoscoviumLivermoriumTennessineOganesson
Rn

Og

(Usb)
tennessineoganessonununennium
Atomic number (Z)118
Groupgroup 18
Periodperiod 7
Blockp-block
Element category  Unknown chemical properties, was expected to be a noble gas; now predicted to be metallic-looking reactive solid, and either a semiconductor (possibly a metalloid) or a post-transition metal[2][3]
Electron configuration[Rn] 5f14 6d10 7s2 7p6 (predicted)[4][5]
Electrons per shell2, 8, 18, 32, 32, 18, 8 (predicted)
Physical properties
Phase at STPsolid (predicted)[4]
Melting point320 K ​(50 °C, ​120 °F) (predicted)[6]
Boiling point350±30 K ​(80±30 °C, ​170±50 °F) (extrapolated)[4]
Density (near r.t.)4.9–5.1 g/cm3 (predicted)[7]
Critical point439 K, 6.8 MPa (extrapolated)[8]
Heat of fusion23.5 kJ/mol (extrapolated)[8]
Heat of vaporization19.4 kJ/mol (extrapolated)[8]
Atomic properties
Oxidation states(−1),[5] (0), (+1),[9] (+2),[10] (+4),[10] (+6)[5] (predicted)
Ionization energies
  • 1st: 860.1 kJ/mol (predicted)[11]
  • 2nd: 1560 kJ/mol (predicted)[12]
Covalent radius157 pm (predicted)[13]
Other properties
Natural occurrencesynthetic
Crystal structureface-centered cubic (fcc)
Face-centered cubic crystal structure for oganesson

(extrapolated)[14]
CAS Number54144-19-3
History
Namingafter Yuri Oganessian
PredictionHans Peter Jørgen Julius Thomsen (1895)
DiscoveryJoint Institute for Nuclear Research and Lawrence Livermore National Laboratory (2002)
Main isotopes of oganesson
Iso­topeAbun­danceHalf-life (t1/2)Decay modePro­duct
294Og[15]syn0.69 ms[16]α290Lv
SF
295Og[17]syn181 ms?α291Lv
| references

Oganesson is a synthetic chemical element with the 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.[18][19] The name is in line with the tradition of honoring a scientist, in this case the nuclear physicist Yuri Oganessian, who has played a leading role in the discovery of the heaviest elements in the periodic table. It is one of only two elements named after a person who was alive at the time of naming, the other being seaborgium, and the only element whose namesake is alive today.[20]

Oganesson has the highest atomic number and highest atomic mass of all known elements. The radioactive oganesson atom is very unstable, and since 2005, only five (possibly six) atoms of the isotope 294Og have been detected.[21] Although this allowed very little experimental characterization of its properties and possible compounds, theoretical calculations have resulted in many predictions, including some surprising ones. For example, although oganesson is a member of group 18 (the noble gases) – the first synthetic element to be so – it may be significantly reactive, unlike all the other elements of that group.[4] It was formerly thought to be a gas under normal conditions but is now predicted to be a solid due to relativistic effects.[4] On the periodic table of the elements it is a p-block element and the last one of period 7.

History

Early speculation

The possibility of a seventh noble gas, after helium, neon, argon, krypton, xenon, and radon was considered almost as soon as the noble gas group was discovered. The Danish chemist Hans Peter Jørgen Julius Thomsen predicted in April 1895, the year after the discovery of argon, that there was a whole series of chemically inert gases similar to argon that would bridge the halogen and alkali metal groups: he expected that the seventh of this series would end a 32-element period which contained thorium and uranium and have an atomic weight of 292, close to the 294 now known for the first and only confirmed isotope of oganesson.[22] Niels Bohr noted in 1922 that this seventh noble gas should have atomic number 118 and predicted its electronic structure as 2, 8, 18, 32, 32, 18, 8, matching modern predictions.[23] Following this, Aristid von Grosse wrote an article in 1965 predicting the likely properties of element 118. It was 107 years from Thomsen's prediction before oganesson was successfully synthesised, although its chemical properties have not been investigated to determine if it behaves as the heavier congener of radon.[12]

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.[24] His calculations suggested that it might be possible to make oganesson 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.[24]

In 1999, researchers at Lawrence Berkeley National Laboratory made use of these predictions and announced the discovery of livermorium and oganesson, in a paper published in Physical Review Letters,[25] and very soon after the results were reported in Science.[26] The researchers reported that they had performed the reaction

+ 293
118
Og
+ .

The following year, they published a retraction after researchers at other laboratories were unable to duplicate the results and the Berkeley lab could not duplicate them either.[27] 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.[28][29] 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.[30]

Discovery reports

The first genuine decay of atoms of oganesson was observed in 2002 at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, by a joint team of Russian and American scientists. Headed by Yuri Oganessian, a Russian nuclear physicist of Armenian ethnicity, the team included American scientists of the Lawrence Livermore National Laboratory, California.[31] 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.[32] On 9 October 2006, the researchers announced[15] that they had indirectly detected a total of three (possibly four) nuclei of oganesson-294 (one or two in 2002[33] and two more in 2005) produced via collisions of californium-249 atoms and calcium-48 ions.[34][35][36][37][38]

+ + 3 .
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.[15] The decay energy and average half-life is given for the parent isotope and each daughter isotope. The fraction of atoms undergoing spontaneous fission (SF) is given in green.

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".[39]

Because of the very small fusion reaction probability (the fusion cross section is ~0.3–0.6 pb or (3–6)×10−41 m2) the experiment took four months and involved a beam dose of 2.5×1019 calcium ions that had to be shot at the californium target to produce the first recorded event believed to be the synthesis of oganesson.[40] 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 100000.[41]

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: 294
Og
decays into Lv by alpha decay. Since there were only three nuclei, the half-life derived from observed lifetimes has a large uncertainty: 0.89+1.07
−0.31
 ms
.[15]

294
118
Og
290
116
Lv
+

The identification of the 294
Og
nuclei was verified by separately creating the putative daughter nucleus 290
Lv
directly by means of a bombardment of Cm with Ca ions,

245
96
Cm
+ 48
20
Ca
290
116
Lv
+ 3 ,

and checking that the 290
Lv
decay matched the decay chain of the 294
Og
nuclei.[15] The daughter nucleus 290
Lv
is very unstable, decaying with a lifetime of 14 milliseconds into Fl, which may experience either spontaneous fission or alpha decay into Cn, which will undergo spontaneous fission.[15]

In a quantum-tunneling model, the alpha decay half-life of 294
Og
was predicted to be 0.66+0.23
−0.18
 ms
[42] with the experimental Q-value published in 2004.[43] Calculation with theoretical Q-values from the macroscopic-microscopic model of Muntian–Hofman–Patyk–Sobiczewski gives somewhat lower but comparable results.[44]

Confirmation

One atom of the heavier isotope 295Og may have been seen in a 2011 experiment at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany aimed at the synthesis of element 120 in the reaction 248Cm+54Cr, but uncertainties in the data meant that the observed chain cannot be definitely assigned to 299120 and 295Og: the data indicates for 295Og a half-life of 181 milliseconds, longer than that of 294Og, which is 0.7 milliseconds.[17]

In December 2015, the Joint Working Party of international scientific bodies International Union of Pure and Applied Chemistry (IUPAC) and International Union of Pure and Applied Physics (IUPAP) recognized the element's discovery and assigned the priority of the discovery to the Dubna–Livermore collaboration.[45] 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.[46]

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 Dubna team planned to repeat this experiment in 2017–2020.[47] 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, a reaction planned at the JINR and at RIKEN in 2017–2018.[47][48][49] A search beginning in summer 2016 at RIKEN for 295Og in the 3n channel of this reaction was unsuccessful, though the study is planned to resume; a detailed analysis and cross section limit were not provided. These heavier and likely more stable isotopes may be useful in probing the chemistry of oganesson.[50][51]

Naming

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).[14] In 1979, IUPAC assigned the systematic placeholder name ununoctium to the undiscovered element, with the corresponding symbol of Uuo,[52] and recommended that it be used until after confirmed discovery of the element.[53] 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 even simply 118.[5]

Before the retraction in 2001, the researchers from Berkeley had intended to name the element ghiorsium (Gh), after Albert Ghiorso (a leading member of the research team).[54]

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.[55] 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.[56] 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.[57] These names were later suggested for element 114 (flerovium) and element 116 (moscovium).[58] Flerovium became the name of element 114; the final name proposed for element 116 was instead livermorium,[59] with moscovium later being proposed and accepted for element 115 instead.[20]

Traditionally, the names of all noble gases end in "-on", with the exception of helium, which was not known to be a noble gas when discovered. The IUPAC guidelines valid at the moment of the discovery approval however required all new elements be named with the ending "-ium", even if they turned out to be halogens (traditionally ending in "-ine") or noble gases (traditionally ending in "-on").[60] 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.[61]

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. 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, 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."[62]

In internal discussions, IUPAC asked the JINR if they wanted the element to be spelled "oganeson" to match the spelling used in Russian more closely. Oganessian and the JINR refused this offer, citing the Soviet-era practice of transliterating names into the Latin alphabet in accordance with the rules of the French language (“Oganessian” is a such a transliteration) and arguing that "oganesson" would be easier to link to the person.[63][a] In June 2016, IUPAC announced that the discoverers planned to give the element the name oganesson (symbol: Og). The name became official on 28 November 2016.[20] In 2017, Oganessian commented on the naming:[64]

For me, it is an honour. The discovery of element 118 was by scientists at the Joint Institute for Nuclear Research in Russia and at the Lawrence Livermore National Laboratory in the US, and it was my colleagues who proposed the name oganesson. My children and grandchildren have been living in the US for decades, but my daughter wrote to me to say that she did not sleep the night she heard because she was crying.[64]

— Yuri Oganessian

The naming ceremony for moscovium, tennessine, and oganesson was held on 2 March 2017 at the Russian Academy of Sciences in Moscow.[65]

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:[63]

Not like much! You see, not like much. It is customary in science to name something new after its discoverer. It’s just that there are few elements, and this happens rarely. But look at how many equations and theorems in mathematics are named after somebody. And in medicine? Alzheimer, Parkinson. There’s nothing special about it.