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{{Infobox unbiquadium}}

'''Unbiquadium''', also known as '''element 124''' or '''eka-uranium''', is a hypothetical chemical element; it has placeholder symbol '''Ubq''' and [[atomic number]] 124. ''Unbiquadium'' and ''Ubq'' are the temporary [[systematic element name|IUPAC name and symbol]], respectively, until the element is discovered, confirmed, and a permanent name is decided upon. In the periodic table, unbiquadium is expected to be a [[g-block]] [[superactinide]] and the sixth element in the 8th [[period (periodic table)|period]]. Unbiquadium has attracted attention, as it may lie within the [[island of stability]], leading to longer half-lives, especially for 308Ubq which is predicted to have a [[Magic number (physics)|magic number]] of [[neutron]]s (184).

Despite several searches, unbiquadium has not been synthesized, nor have any naturally occurring [[isotope]]s been found to exist. It is believed that the synthesis of unbiquadium will be far more challenging than that of [[extended periodic table|lighter undiscovered elements]], and nuclear instability may pose further difficulties in identifying unbiquadium, unless the island of stability has a stronger stabilizing effect than predicted in this region.

As a member of the superactinide series, unbiquadium is expected to bear some resemblance to its possible lighter [[congener (chemistry)|congener]] [[uranium]]. The valence electrons of unbiquadium are expected to participate in chemical reactions fairly easily, though [[relativistic quantum chemistry|relativistic effects]] may significantly influence some of its properties; for example, the electron configuration has been calculated to differ considerably from the one predicted by the [[Aufbau principle]].

==Introduction==
{{Excerpt|Superheavy element|Introduction|subsections=yes}}

==History==
===Synthesis attempts===
Because complete nuclear shells (or, equivalently, a [[magic number (physics)|magic number]] of [[proton]]s or [[neutron]]s) may confer additional stability on the nuclei of superheavy elements, moving closer to the center of the [[island of stability]], it was thought that the synthesis of element 124 or nearby elements would populate longer-lived nuclei within the island. Scientists at [[GANIL]] (Grand Accélérateur National d'Ions Lourds) attempted to measure the direct and delayed fission of compound nuclei of elements with ''Z'' = 114, 120, and 124 in order to probe [[nuclear shell|shell]] effects in this region and to pinpoint the next spherical proton shell. In 2006, with full results published in 2008, the team provided results from a reaction involving the bombardment of a natural [[germanium]] target with uranium ions:<ref name="emsley">{{cite book|last=Emsley|first=John|title=Nature's Building Blocks: An A-Z Guide to the Elements|edition=New|year=2011|publisher=Oxford University Press|location=New York, NY|isbn=978-0-19-960563-7|page=588}}</ref>

:{{nuclide|uranium|238}} + {{nuclide|germanium|''nat''}} → {{SimpleNuclide|unbiquadium|308,310,311,312,314}}* → ''fission''

The team reported that they had been able to identify [[compound nucleus|compound nuclei]] fissioning with half-lives > 10−18 s. This result suggests a strong stabilizing effect at ''Z'' = 124 and points to the next proton shell at ''Z'' > 120, not at ''Z'' = 114 as previously thought. A compound nucleus is a loose combination of [[nucleon]]s that have not arranged themselves into nuclear shells yet. It has no internal structure and is held together only by the collision forces between the target and projectile nuclei. It is estimated that it requires around 10−14 s for the nucleons to arrange themselves into nuclear shells, at which point the compound nucleus becomes a [[nuclide]], and this number is used by [[IUPAC]] as the minimum [[half-life]] a claimed isotope must have to potentially be recognised as being discovered. Thus, the GANIL experiments do not count as a discovery of element 124.<ref name="emsley"/>

The fission of the compound nucleus 312124 was also studied in 2006 at the tandem ALPI heavy-ion accelerator at the [[Laboratori Nazionali di Legnaro]] (Legnaro National Laboratories) in Italy:<ref name=thomas>{{cite journal|display-authors=3|last1=Thomas|first1=R.G.|last2=Saxena|first2=A. |last3=Sahu|first3=P.K.|last4=Choudhury|first4=R.K.|last5=Govil|first5=I.M. |last6=Kailas|first6=S.|last7=Kapoor|first7=S.S.|last8=Barubi|first8=M. |last9=Cinausero|first9=M.|last10=Prete|first10=G.|last11=Rizzi|first11=V. |last12=Fabris|first12=D.|last13=Lunardon|first13=M.|last14=Moretto|first14=S. |last15=Viesti|first15=G.|last16=Nebbia|first16=G.|last17=Pesente|first17=S. |last18=Dalena|first18=B.|last19=D'Erasmo|first19=G.|last20=Fiore|first20=E.M. |last21=Palomba|first21=M.|last22=Pantaleo|first22=A.|last23=Paticchio|first23=V. |last24=Simonetti|first24=G.|last25=Gelli|first25=N.|last26=Lucarelli|first26=F. |date=2007|title=Fission and binary fragmentation reactions in 80Se+208Pb and 80Se+232Th systems |journal=Physical Review C |volume=75|pages=024604–1–024604–9|doi=10.1103/PhysRevC.75.024604|hdl=2158/776924|hdl-access=free}}</ref>

:{{nuclide|thorium|232}} + {{nuclide|selenium|80}} → {{SimpleNuclide|unbiquadium|312}}* → ''fission''

Similarly to previous experiments conducted at the JINR ([[Joint Institute for Nuclear Research]]), [[fission product|fission fragments]] clustered around [[doubly magic]] nuclei such as 132Sn (''Z'' = 50, ''N'' = 82), revealing a tendency for superheavy nuclei to expel such doubly magic nuclei in fission.<ref>see Flerov lab annual reports 2000–2004 inclusive http://www1.jinr.ru/Reports/Reports_eng_arh.html</ref> The average number of neutrons per fission from the 312124 compound nucleus (relative to lighter systems) was also found to increase, confirming that the trend of heavier nuclei emitting more neutrons during fission continues into the superheavy mass region.<ref name=thomas />

===Possible natural occurrence===
A study in 1976 by a group of American researchers from several universities proposed that [[primordial element|primordial]] superheavy elements, mainly [[livermorium]], unbiquadium, [[unbihexium]], and [[unbiseptium]], could be a cause of unexplained radiation damage (particularly [[radiohalos]]) in minerals.{{sfn|Hoffman|Ghiorso|Seaborg|2000|p=413}} Unbiquadium was then suggested to exist in nature with its possible [[congener (chemistry)|congener]] uranium in detectable quantities, at a relative abundance of 10−11.<ref name=symposium /> Such unbiquadium nuclei were thought to undergo alpha decay with very long half-lives down to [[flerovium]], which would then exist in natural [[lead]] at a similar concentration (10−11) and undergo [[spontaneous fission]].<ref name=symposium>{{cite book |editor1-last=Lodhi |editor1-first=M.A.K. |title=Superheavy Elements: Proceedings of the International Symposium on Superheavy Elements |location= Lubbock, Texas |publisher=Pergamon Press |date=March 1978 |isbn=0-08-022946-8}}</ref><ref name=fossilfission>{{cite web|last1=Maly|first1=J. |last2=Walz|first2=D.R. |title=Search for superheavy elements among fossil fission tracks in zircon|date=1980|url=http://www.slac.stanford.edu/pubs/slacpubs/2500/slac-pub-2554.pdf}}</ref> This prompted many researchers to search for them in nature from 1976 to 1983. A group led by Tom Cahill, a professor at the [[University of California at Davis]], claimed in 1976 that they had detected [[alpha particle]]s and [[X-rays]] with the right energies to cause the damage observed, supporting the presence of these elements. Others claimed that none had been detected, and questioned the proposed characteristics of primordial superheavy nuclei.{{sfn|Hoffman|Ghiorso|Seaborg|2000|p=416–417}} In particular, they cited that the magic number ''N'' = 228 necessary for enhanced stability would create a neutron-excessive nucleus in unbiquadium that would not be [[beta-decay stable isobars|beta-stable]]. This activity was also proposed to be caused by nuclear transmutations in natural [[cerium]], raising further ambiguity upon this claimed observation of superheavy elements.{{sfn|Hoffman|Ghiorso|Seaborg|2000|p=417}}

The possible extent of primordial superheavy elements on Earth today is uncertain. Even if they are confirmed to have caused the radiation damage long ago, they might now have decayed to mere traces, or even be completely gone.<ref name="emsley2">{{cite book|last=Emsley|first=John|title=Nature's Building Blocks: An A–Z Guide to the Elements |edition=New |year=2011 |publisher=Oxford University Press|location=New York |isbn=978-0-19-960563-7|page=592}}</ref> It is also uncertain if such superheavy nuclei may be produced naturally at all, as spontaneous fission is expected to terminate the [[r-process]] responsible for heavy element formation between [[mass number]] 270 and 290, well before elements such as unbiquadium may be formed.<ref>{{cite journal|display-authors=3|last1=Petermann |first1=I|last2=Langanke|first2=K. |last3=Martínez-Pinedo|first3=G.|last4=Panov|first4=I.V |last5=Reinhard|first5=P.G. |last6=Thielemann |first6=F.K.|date=2012|title=Have superheavy elements been produced in nature?|journal=European Physical Journal A|volume=48|issue=122|page=122 |doi=10.1140/epja/i2012-12122-6 |arxiv=1207.3432 |bibcode=2012EPJA...48..122P |s2cid=119264543 |url=https://www.researchgate.net/publication/229156774}}</ref>

===Naming===
Using the 1979 IUPAC [[systematic element name|recommendations]], the element should be [[placeholder name|temporarily called]] ''unbiquadium'' (symbol ''Ubq'') until it is discovered, the discovery is confirmed, and a permanent name chosen.<ref name="iupac">{{cite journal |last=Chatt |first=J. |journal=Pure and Applied Chemistry |date=1979 |volume=51 |pages=381–384 |title=Recommendations for the naming of elements of atomic numbers greater than 100 |doi=10.1351/pac197951020381 |issue=2 |doi-access=free }}</ref> Although widely used in the chemical community on all levels, from chemistry classrooms to advanced textbooks, the recommendations are mostly ignored among scientists who work theoretically or experimentally on superheavy elements, who call it "element 124", with the symbol ''E124'', ''(124)'', or ''124''.<ref name=Haire>{{cite book| title=The Chemistry of the Actinide and Transactinide Elements| editor1-last=Morss| editor2-first=Norman M.| editor2-last=Edelstein| editor3-last=Fuger| editor3-first=Jean| last=Haire |first=Richard G.| chapter=Transactinides and the future elements| publisher=[[Springer Science+Business Media]]| year=2006| page=1724| isbn=1-4020-3555-1| location=Dordrecht, The Netherlands| edition=3rd}}</ref> Some researchers have also referred to unbiquadium as ''eka-uranium'',<ref name=fossilfission /> a name derived from [[Mendeleev's predicted elements|the system Dmitri Mendeleev used]] to predict unknown elements, though such an extrapolation might not work for g-block elements with no known congeners and ''eka-uranium'' would instead refer to element 144<ref name="Fricke" /> or 146<ref name=nefedov>{{cite journal |last1=Nefedov |first1=V.I. |last2=Trzhaskovskaya |first2=M.B. |last3=Yarzhemskii |first3=V.G. |title=Electronic Configurations and the Periodic Table for Superheavy Elements |journal=Doklady Physical Chemistry |date=2006 |volume=408 |issue=2 |pages=149–151 |doi=10.1134/S0012501606060029 |s2cid=95738861 |issn=0012-5016 |url=http://www.primefan.ru/stuff/chem/nefedov.pdf}}</ref> when the term is meant to denote the element directly below uranium.

==Prospects for future synthesis==
Every element from [[mendelevium]] onward was produced in fusion-evaporation reactions, culminating in the discovery of the heaviest known element [[oganesson]] in 2002<ref>{{cite web|title=Element 118: results from the first {{SimpleNuclide|Californium|249}} + {{SimpleNuclide|Calcium|48}} experiment|last1=Oganessian |first1=YT|author-link=Yuri Oganessian |display-authors=etal |publisher=Communication of the Joint Institute for Nuclear Research |date=2002 |url=http://159.93.28.88/linkc/118/anno.html |url-status=dead |archive-url=https://web.archive.org/web/20110722060249/http://159.93.28.88/linkc/118/anno.html |archive-date=22 July 2011}}</ref><ref>{{cite press release|title=Livermore scientists team with Russia to discover element 118|date=3 December 2006|url=https://www.llnl.gov/news/newsreleases/2006/NR-06-10-03.html|publisher=Livermore|access-date=18 January 2008|archive-date=17 October 2011|archive-url=https://web.archive.org/web/20111017105348/https://www.llnl.gov/news/newsreleases/2006/NR-06-10-03.html|url-status=dead}}</ref> and more recently [[tennessine]] in 2010.<ref>{{cite journal|last1=Oganessian|first1=YT|last2=Abdullin|first2=F|last3=Bailey|first3=PD|display-authors=etal |date=April 2010|title=Synthesis of a New Element with Atomic Number 117 |format=PDF |url=https://www.researchgate.net/publication/44610795 |journal=Physical Review Letters |volume=104|issue=142502|pages=142502 |bibcode=2010PhRvL.104n2502O |doi=10.1103/PhysRevLett.104.142502 |pmid=20481935|doi-access=free}}</ref> These reactions approached the limit of current technology; for example, the synthesis of tennessine required 22 milligrams of 249Bk and an intense 48Ca beam for six months. The intensity of beams in superheavy element research cannot exceed 1012 projectiles per second without damaging the target and detector, and producing larger quantities of increasingly rare and unstable [[actinide]] targets is impractical.<ref name=Roberto>{{cite web |title=Actinide Targets for Super-Heavy Element Research |last=Roberto |first=JB |date=2015 |website=cyclotron.tamu.edu |publisher=Texas A & M University |access-date=30 October 2018 |url=http://cyclotron.tamu.edu/she2015/assets/pdfs/presentations/Roberto_SHE_2015_TAMU.pdf}}</ref>
Consequently, future experiments must be done at facilities such as the superheavy element factory (SHE-factory) at the [[Joint Institute for Nuclear Research]] (JINR) or [[RIKEN]], which will allow experiments to run for longer stretches of time with increased detection capabilities and enable otherwise inaccessible reactions.<ref>{{cite web |title=平成23年度研究業績レビュー（中間レビュー）の実施について |language=ja |trans-title=Implementation of the 2011 Research Achievement Review (Interim Review) |last1=Hagino |first1=Kouichi |last2=Hofmann |first2=Sigurd |last3=Miyatake |first3=Hiroari |last4=Nakahara |first4=Hiromichi |date=July 2012 |website=www.riken.jp |publisher=RIKEN |access-date=5 May 2017 |url= http://www.riken.jp/~/media/riken/about/reports/evaluation/rnc/rep/rnc-morita2012-report-e.pdf |archive-url=https://web.archive.org/web/20190330183221/http://www.riken.jp/~/media/riken/about/reports/evaluation/rnc/rep/rnc-morita2012-report-e.pdf |archive-date=2019-03-30 |url-status=dead}}</ref> Even so, it is expected to be a great challenge to continue past elements [[unbinilium|120]] or [[unbiunium|121]] given short predicted half-lives and low predicted cross sections.<ref name=Karpov>{{cite web |url=http://cyclotron.tamu.edu/she2015/assets/pdfs/presentations/Karpov_SHE_2015_TAMU.pdf |title=Superheavy Nuclei: which regions of nuclear map are accessible in the nearest studies |last1=Karpov |first1=A |last2=Zagrebaev |first2=V |last3=Greiner |first3=W |date=2015 |website=cyclotron.tamu.edu |publisher=Texas A & M University |access-date=30 October 2018}}</ref>

The production of new superheavy elements will require projectiles heavier than 48Ca, which was successfully used in the discovery of elements 114–118, though this necessitates more symmetric reactions which are less favorable.{{sfn|Zagrebaev|Karpov|Greiner|2013}} Hence, it is likely that the reactions between 58Fe and a 249[[californium|Cf]]<ref name=Karpov /> or 251Cf target are most promising.<ref name=researchSH>{{cite web |url=https://people.nscl.msu.edu/~iwasaki/EBSS2016/KR_EBSS2016.pdf |title=Super Heavy Elements and Nuclei |last=Rykaczewski |first=Krzysztof P. |date=July 2016 |website=people.nscl.msu.edu |publisher=MSU |access-date=30 April 2017}}</ref> Studies on the fission of various superheavy [[compound nucleus|compound nuclei]] have found that the dynamics of 48Ca- and 58Fe-induced reactions are similar, suggesting that 58Fe projectiles may be viable in producing superheavy nuclei up to ''Z'' = 124 or possibly 125.<ref name=Roberto /><ref>{{cite web |url=http://www1.jinr.ru/Reports/Reports_eng_arh.html |title=JINR Publishing Department: Annual Reports (Archive) |author=JINR |date=1998–2014 |website=jinr.ru |publisher=JINR |access-date=23 September 2016}}</ref> It is also possible that a reaction with 251Cf will produce the compound nucleus 309Ubq* with 185 neutrons, immediately above the ''N'' = 184 shell closure. For this reason, the compound nucleus is predicted to have relatively high survival probability and low neutron separation energy, leading to the 1n–3n channels and isotopes 306–308Ubq with a relatively high cross section.<ref name=researchSH /> These dynamics are highly speculative, as the cross section may be far lower should trends in the production of elements 112–118 continue or the [[fission barrier]]s be lower than expected, regardless of shell effects, leading to decreased stability against spontaneous fission (which is of growing importance).<ref name=Karpov /> Nonetheless, the prospect of reaching the ''N'' = 184 shell on the proton-rich side of the chart of nuclides by increasing proton number has long been considered; already in 1970, Soviet nuclear physicist [[Georgy Flyorov]] suggested bombarding a plutonium target with zinc projectiles to produce isotopes of element 124 at the ''N'' = 184 shell.<ref>{{cite web |title=Synthesis and Search for Heavy Transuranium Elements |last=Flerov |first=G. N. |date=1970 |website=jinr.ru |url=http://fls2.jinr.ru/linkc/flnr_presentations/articles/synth_elm.pdf |access-date=23 November 2018}}</ref>

==Predicted properties==
===Nuclear stability and isotopes===
[[File:Nuclear chart from KTUY model.svg|thumb|right|400px|This nuclear chart used by the [[Japan Atomic Energy Agency]] predicts the decay modes of nuclei up to ''Z'' = 149 and ''N'' = 256. For unbiquadium (''Z'' = 124), there are predicted regions of increased stability around ''N'' = 184 and ''N'' = 228, though many intermediate isotopes are theoretically susceptible to spontaneous fission with half-lives shorter than 1 [[nanosecond]].<ref name=SHlimit />]]

Unbiquadium is of interest to researchers because of its possible location near the center of an [[island of stability]], a theoretical region comprising longer-lived superheavy nuclei. Such an island of stability was first proposed by [[University of California, Berkeley|University of California]] professor [[Glenn Seaborg]],<ref>{{cite book|title=Van Nostrand's scientific encyclopedia|first1=Glenn D. |last1= Considine |first2=Peter H. |last2= Kulik|publisher=Wiley-Interscience |year=2002|edition=9|isbn=978-0-471-33230-5|oclc=223349096}}</ref> specifically predicting a region of stability centered at element 126 ([[unbihexium]]) and encompassing nearby elements, including unbiquadium, with half-lives possibly as long as 109 years.<ref name=symposium /> In known elements, the stability of nuclei decreases greatly with the increase in atomic number after [[uranium]], the heaviest [[primordial element]], so that all observed isotopes with an atomic number above [[mendelevium|101]] [[radioactive decay|decay radioactively]] with a [[half-life]] under a day. Nevertheless, there is a slight increase in nuclear stability in nuclides around atomic numbers [[darmstadtium|110]]–[[flerovium|114]], which suggests the presence of an island of stability. This is attributed to the possible closure of [[nuclear shell model|nuclear shells]] in the [[superheavy element|superheavy]] mass region, with stabilizing effects that may lead to half-lives on the order of years or longer for some as-yet undiscovered isotopes of these elements.<ref name=symposium />{{sfn|Zagrebaev|Karpov|Greiner|2013}} While still unproven, the existence of superheavy elements as heavy as [[oganesson]] provides evidence of such stabilizing effects, as elements with an atomic number greater than approximately [[rutherfordium|104]] are extremely unstable in [[semi-empirical mass formula|models]] neglecting magic numbers.<ref name=liquiddrop>{{cite journal |last=Möller|first=P. |date=2016|title=The limits of the nuclear chart set by fission and alpha decay|journal=EPJ Web of Conferences|volume=131 |pages=03002:1–8 |doi=10.1051/epjconf/201613103002 |bibcode=2016EPJWC.13103002M |url=http://inspirehep.net/record/1502715/files/epjconf-NS160-03002.pdf|doi-access=free}}</ref>

In this region of the periodic table, ''N'' = 184 and ''N'' = 228 have been proposed as closed neutron shells,<ref name=magickoura>{{cite journal|last1=Koura|first1=H.|last2=Chiba|first2=S. |title=Single-Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region |journal=Journal of the Physical Society of Japan|volume=82|at=014201|date=2013|issue=1 |doi=10.7566/JPSJ.82.014201 |bibcode=2013JPSJ...82a4201K |url=https://www.researchgate.net/publication/258799250}}</ref> and various atomic numbers have been proposed as closed proton shells, including ''Z'' = 124.{{efn|Atomic numbers 114, 120, 122, and 126 have also been proposed as closed proton shells in different models.}} The island of stability is characterized by longer half-lives of nuclei located near these magic numbers, though the extent of stabilizing effects is uncertain due to predictions of weakening of the proton shell closures and possible loss of [[doubly magic|double magicity]].<ref name=magickoura /> More recent research predicts the island of stability to instead be centered at [[Beta-decay stable isobars|beta-stable]] [[copernicium]] isotopes 291Cn and 293Cn,{{sfn|Zagrebaev|Karpov|Greiner |2013}}<ref name=Palenzuela>{{cite journal|last1=Palenzuela|first1=Y. M.|last2=Ruiz|first2=L. F.|last3=Karpov |first3=A.|last4=Greiner|first4=W.|year=2012|title=Systematic Study of Decay Properties of Heaviest Elements|journal=Bulletin of the Russian Academy of Sciences: Physics|volume=76|issue=11|pages=1165–1171 |url=http://nrv.jinr.ru/karpov/publications/Palenzuela12_BRAS.pdf|doi=10.3103/s1062873812110172 |bibcode=2012BRASP..76.1165P |s2cid=120690838|issn=1062-8738}}</ref> which would place unbiquadium well above the island and result in short half-lives regardless of shell effects. A 2016 study on the decay properties of unbiquadium isotopes 284–339Ubq predicts that 284–304Ubq lie outside the [[proton drip line]] and thus may be [[proton emission|proton emitters]], 305–323Ubq may undergo [[alpha decay]], with some chains terminating as far as [[flerovium]], and heavier isotopes will decay by [[spontaneous fission]].<ref name=Santhosh>{{Cite journal |last1=Santhosh|first1=K.P.|last2=Priyanka|first2=B.|last3=Nithya|first3=C.|date=2016 |title=Feasibility of observing the α decay chains from isotopes of SHN with Z = 128, Z = 126, Z = 124 and Z = 122|journal=Nuclear Physics A|volume=955 |issue=November 2016|pages=156–180|doi=10.1016/j.nuclphysa.2016.06.010|bibcode=2016NuPhA.955..156S |arxiv=1609.05498|s2cid=119219218}}</ref> These results, as well as those from a quantum-tunneling model, predict no half-lives over a millisecond for isotopes lighter than 319Ubq,<ref>{{cite journal|journal=[[Atomic Data and Nuclear Data Tables]] |volume=94|pages=781–806|date=2008 |title=Nuclear half-lives for α -radioactivity of elements with 100 ≤ Z ≤ 130|author=Chowdhury, R.P.|author2=Samanta, C.|author3=Basu, D.N. |doi=10.1016/j.adt.2008.01.003|bibcode=2008ADNDT..94..781C|issue=6|arxiv = 0802.4161|s2cid=96718440 }}</ref> as well as especially short half-lives for 309–314Ubq in the sub-microsecond range<ref name=Santhosh /> due to destabilizing effects immediately above the shell at ''N'' = 184. This renders the identification of many unbiquadium isotopes nearly impossible with current technology, as detectors cannot distinguish rapid successive signals from alpha decays in a time period shorter than microseconds.<ref name=Karpov />{{efn|While such nuclei may be synthesized and a [[decay chain|series]] of decay signals may be registered, decays faster than one microsecond may pile up with subsequent signals and thus be indistinguishable, especially when multiple uncharacterized nuclei may be formed and emit a series of similar alpha particles. The main difficulty is thus attributing the decays to the correct [[parent nuclide|parent]] nucleus, as a superheavy atom that decays before reaching the detector will not be registered at all.}}

Increasingly short [[spontaneous fission]] half-lives of superheavy nuclei and the possible domination of fission over alpha decay will also probably determine the stability of unbiquadium isotopes.<ref name=Karpov /><ref name=Palenzuela /> While some fission half-lives constituting a "sea of instability" may be on the order of 10−18 s as a consequence of very low [[fission barrier]]s, especially in [[Even and odd atomic nuclei|even–even nuclei]] due to pairing effects, stabilizing effects at ''N'' = 184 and ''N'' = 228 may allow the existence of relatively long-lived isotopes.<ref name=SHlimit>{{cite conference| last=Koura|first=H. |date=2011|title=Decay modes and a limit of existence of nuclei in the superheavy mass region|conference=4th International Conference on the Chemistry and Physics of the Transactinide Elements |url=http://tan11.jinr.ru/pdf/10_Sep/S_2/05_Koura.pdf |access-date=18 November 2018}}</ref> For ''N'' = 184, fission half-lives may increase, though alpha half-lives are still expected to be on the order of microseconds or less, despite the shell closure at 308Ubq. It is also possible that the island of stability may shift to the ''N'' = 198 region, where total half-lives may be on the order of seconds,<ref name=Palenzuela /> in contrast to neighboring isotopes that would undergo fission in less than a microsecond. In the neutron-rich region around ''N'' = 228, alpha half-lives are also predicted to increase with increasing [[neutron number]], meaning that the stability of such nuclei would primarily depend on the location of the [[beta-stability line]] and resistance to fission. One early calculation by P. Moller, a physicist at [[Los Alamos National Laboratory]], estimates the total half-life of 352Ubq (with ''N'' = 228) to be around 67 seconds, and possibly the longest in the ''N'' = 228 region.<ref name=symposium /><ref name=quest>{{cite journal|last1=Bemis|first1=C.E. |last2=Nix|first2=J.R.|date=1977|title=Superheavy elements - the quest in perspective|journal=Comments on Nuclear and Particle Physics|volume=7|issue=3|pages=65–78 |url=http://inspirehep.net/record/1382449/files/v7-n3-p65.pdf |issn=0010-2709}}</ref>

===Chemical===
Unbiquadium is the fourth member of the superactinide series and should be similar to [[uranium]]: both elements have six valence electrons over a noble gas core. In the superactinide series, the [[Aufbau principle]] is expected to break down due to [[relativistic quantum chemistry|relativistic effects]], and an overlap of the 5g, 6f, 7d, and 8p orbitals is expected. The ground state electron configuration of unbiquadium is thus predicted to be [[[oganesson|Og]]] 6f3 8s2 8p1<ref name=Hoffman>{{cite book| title=The Chemistry of the Actinide and Transactinide Elements| editor1-last=Morss|editor2-first=Norman M.| editor2-last=Edelstein| editor3-last=Fuger|editor3-first=Jean| last1=Hoffman|first1=Darleane C. |last2=Lee |first2=Diana M. |last3=Pershina |first3=Valeria| chapter=Transactinides and the future elements| publisher= [[Springer Science+Business Media]]| year=2006| isbn=1-4020-3555-1| location=Dordrecht, The Netherlands| edition=3rd}}</ref> or 6f2 8s2 8p2,<ref>{{cite journal |last1=Umemoto |first1=Koichiro |last2=Saito |first2=Susumu |date=1996 |title=Electronic Configurations of Superheavy Elements |url=https://journals.jps.jp/doi/pdf/10.1143/JPSJ.65.3175 |journal=Journal of the Physical Society of Japan |volume=65 |issue=10 |pages=3175–9 |doi=10.1143/JPSJ.65.3175 |bibcode=1996JPSJ...65.3175U |access-date=31 January 2021}}</ref> in contrast to [[[oganesson|Og]]] 5g4 8s2 derived from Aufbau. This predicted overlap of orbitals and uncertainty in order of filling, especially for f and g orbitals, renders predictions of chemical and atomic properties of these elements very difficult.<ref name=EB>{{cite web|author=Seaborg|url=http://www.britannica.com/EBchecked/topic/603220/transuranium-element|title=transuranium element (chemical element)|publisher=Encyclopædia Britannica|date=c. 2006|access-date=2010-03-16}}</ref>

One predicted [[oxidation state]] of unbiquadium is +6, which would exist in the [[halide]]s UbqX6 (X = a halogen), analogous to the known +6 oxidation state in uranium.<ref name="Pyykkö2011"/> Like the other early superactinides, the binding energies of unbiquadium's valence electrons are predicted to be small enough that all six should easily participate in chemical reactions.<ref name="Fricke">{{cite journal |last1=Fricke |first1=B. |last2=Greiner |first2=W. |last3=Waber |first3=J. T. |year=1971 |title=The continuation of the periodic table up to Z = 172. The chemistry of superheavy elements |journal=Theoretica Chimica Acta |volume=21 |issue=3 |pages=235–260 |doi=10.1007/BF01172015|s2cid=117157377 }}</ref> The predicted electron configuration of the Ubq5+ ion is [Og] 6f1.<ref name="Pyykkö2011" />

==Notes==
{{notelist}}

==References==
{{reflist|refs=

<ref name="Pyykkö2011">{{Cite journal|last1=Pyykkö|first1=Pekka|author-link=Pekka Pyykkö|title=A suggested periodic table up to Z ≤ 172, based on Dirac–Fock calculations on atoms and ions|journal=Physical Chemistry Chemical Physics|volume=13|issue=1|pages=161–8|year=2011|pmid=20967377|doi=10.1039/c0cp01575j|bibcode = 2011PCCP...13..161P }}</ref>

}}

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{{Extended periodic table (by Fricke, 32 columns, compact)}}

[[Category:Unbiquadium| ]]
[[Category:Hypothetical chemical elements|124]]

Unbiquadium - Revision history

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