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==Predicted properties of eighth-period elements== Element 118, [[oganesson]], is the heaviest element that has been synthesized. The next two elements, [[ununennium|elements 119]] and [[unbinilium|120]], should form an 8s series and be an [[alkali metal|alkali]] and [[alkaline earth metal]], respectively. Beyond element 120, the [[superactinide]] series is expected to begin, when the 8s electrons and the filling of the 8p<sub>1/2</sub>, 7d<sub>3/2</sub>, 6f, and 5g subshells determine the chemistry of these elements. Complete and accurate [[Coupled cluster#Types of coupled-cluster methods|CCSD]] calculations are not available for elements beyond 122 because of the extreme complexity of the situation: the 5g, 6f, and 7d orbitals should have about the same energy level, and in the region of element 160, the 9s, 8p<sub>3/2</sub>, and 9p<sub>1/2</sub> orbitals should also be about equal in energy. This will cause the electron shells to mix so that the [[block (periodic table)|block]] concept no longer applies very well, and will also result in novel chemical properties that will make positioning some of these elements in a periodic table very difficult.<ref name=Haire/> [[File:Energy eigenvalues superheavy.svg|thumb|center|640px|Energy eigenvalues (in eV) for the outermost electrons of elements with Z = 100 through 172, predicted using Dirac–Fock calculations. The − and + signs refer to orbitals with decreased or increased azimuthal quantum number from spin–orbit splitting respectively: p− is p<sub>1/2</sub>, p+ is p<sub>3/2</sub>, d− is d<sub>3/2</sub>, d+ is d<sub>5/2</sub>, f− is f<sub>5/2</sub>, f+ is f<sub>7/2</sub>, g− is g<sub>7/2</sub>, and g+ is g<sub>9/2</sub>.<ref name=BFricke/>]] ===Chemical and physical properties=== ====Elements 119 and 120==== {{main|Ununennium|Unbinilium}} <div style="float: right; margin: 1px; font-size:85%;"> :{| class="wikitable" |+ Some predicted properties of elements 119 and 120<ref name="Fricke"/><ref name=Haire/> ! Property ! 119 ! 120 |- ! [[Standard atomic weight]] | [322] | [325] |- ! [[Periodic table group|Group]] | [[alkali metal|1]] | [[alkaline earth metal|2]] |- ! Valence [[electron configuration]] | 8s<sup>1</sup> | 8s<sup>2</sup> |- ! Stable [[oxidation state]]s | '''1''', 3 | '''2''', 4 |- ! First [[ionization energy]] | 463.1 [[kilojoule per mole|kJ/mol]] | 563.3 kJ/mol |- ! [[Metallic radius]] | 260 pm | 200 pm |- ! [[Density]] | 3 g/cm<sup>3</sup> | 7 g/cm<sup>3</sup> |- ! [[Melting point]] | {{convert|0–30|C|F|sigfig=2}} | {{convert|680|C|F|sigfig=2}} |-sigfig= ! [[Boiling point]] | {{convert|630|C|F|sigfig=2}} | {{convert|1700|C|F|sigfig=2}} |} </div> The first two elements of period 8 will be ununennium and unbinilium, elements 119 and 120. Their [[electron configuration]]s should have the 8s orbital being filled. This orbital is relativistically stabilized and contracted; thus, elements 119 and 120 should be more like [[rubidium]] and [[strontium]] than their immediate neighbours above, [[francium]] and [[radium]]. Another effect of the relativistic contraction of the 8s orbital is that the [[atomic radius|atomic radii]] of these two elements should be about the same as those of francium and radium. They should behave like normal [[alkali metal|alkali]] and [[alkaline earth metal]]s (albeit less reactive than their immediate vertical neighbours), normally forming +1 and +2 [[oxidation state]]s, respectively, but the relativistic destabilization of the 7p<sub>3/2</sub> subshell and the relatively low [[ionization energy|ionization energies]] of the 7p<sub>3/2</sub> electrons should make higher oxidation states like +3 and +4 (respectively) possible as well.<ref name="Fricke"/><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| 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=978-1-4020-3555-5| location=Dordrecht, The Netherlands| edition=3rd| ref=CITEREFHaire2006}}</ref> ====Superactinides==== The superactinides may range from elements 121 through 157, which can be classified as the 5g and 6f elements of the eighth period, together with the first 7d element.<ref name=nefedov/> In the superactinide series, the 7d{{sub|3/2}}, 8p{{sub|1/2}}, 6f{{sub|5/2}} and 5g{{sub|7/2}} shells should all fill simultaneously.<ref name="BFricke"/> This creates very complicated situations, so much so that complete and accurate CCSD calculations have been done only for elements 121 and 122.<ref name=Haire/> The first superactinide, [[unbiunium]] or eka-actinium (element 121), should be similar to [[lanthanum]] and [[actinium]]:<ref>{{Cite journal | last1 = Waber | first1 = J. T. | title = SCF Dirac–Slater Calculations of the Translawrencium Elements | doi = 10.1063/1.1672054 | journal = The Journal of Chemical Physics | volume = 51 | issue = 2 | page = 664| year = 1969 |bibcode = 1969JChPh..51..664W }}</ref> its main oxidation state should be +3, although the closeness of the valence subshells' energy levels may permit higher oxidation states, just as in elements 119 and 120.<ref name=Haire/> Relativistic stabilization of the 8p subshell should result in a ground-state 8s{{sup|2}}8p{{sup|1}} valence electron configuration for element 121, in contrast to the ds{{sup|2}} configurations of lanthanum and actinium;<ref name=Haire/> nevertheless, this anomalous configuration does not appear to affect its calculated chemistry, which remains similar to that of actinium.<ref name=Amador>{{cite journal |last1=Amador |first1=Davi H. T. |last2=de Oliveira |first2=Heibbe C. B. |first3=Julio R. |last3=Sambrano |first4=Ricardo |last4=Gargano |first5=Luiz Guilherme M. |last5=de Macedo |date=12 September 2016 |title=4-Component correlated all-electron study on Eka-actinium Fluoride (E121F) including Gaunt interaction: Accurate analytical form, bonding and influence on rovibrational spectra |journal=Chemical Physics Letters |volume=662 |pages=169–175 |doi=10.1016/j.cplett.2016.09.025|bibcode=2016CPL...662..169A |hdl=11449/168956 |hdl-access=free }}</ref> Its first [[ionization energy]] is predicted to be 429.4 kJ/mol, which would be lower than those of all known elements except for the [[alkali metals]] [[potassium]], [[rubidium]], [[caesium]], and [[francium]]: this value is even lower than that of the period 8 alkali metal ununennium (463.1 kJ/mol). Similarly, the next superactinide, [[unbibium]] or eka-thorium (element 122), may be similar to [[cerium]] and [[thorium]], with a main oxidation state of +4, but would have a ground-state 7d{{sup|1}}8s{{sup|2}}8p{{sup|1}} or 8s{{sup|2}}8p{{sup|2}} valence electron configuration,<ref name="Umemoto">{{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 |bibcode=1996JPSJ...65.3175U |doi=10.1143/JPSJ.65.3175 |access-date=31 January 2021|url-access=subscription }}</ref> unlike thorium's 6d{{sup|2}}7s{{sup|2}} configuration. Hence, its first [[ionization energy]] would be smaller than thorium's (Th: 6.3 [[electronvolt|eV]]; element 122: 5.6 eV) because of the greater ease of ionizing unbibium's 8p{{sub|1/2}} electron than thorium's 6d electron.<ref name=Haire/> The collapse of the 5g orbital itself is delayed until around element 125 ([[wikt:unbipentium|unbipentium]] or eka-neptunium); the electron configurations of the 119-electron isoelectronic series are expected to be [Og]8s{{sup|1}} for elements 119 through 122, [Og]6f{{sup|1}} for elements 123 and 124, and [Og]5g{{sup|1}} for element 125 onwards.<ref name=5gchem/> In the first few superactinides, the binding energies of the added electrons are predicted to be small enough that they can lose all their valence electrons; for example, [[unbihexium]] (element 126) could easily form a +8 oxidation state, and even higher oxidation states for the next few elements may be possible. Element 126 is also predicted to display a variety of other [[oxidation state]]s: recent calculations have suggested a stable [[Fluoride|monofluoride]] 126F may be possible, resulting from a bonding interaction between the 5g [[Atomic orbital|orbital]] on element 126 and the 2[[p-orbital|p]] orbital on [[fluorine]].<ref name=Jacoby>{{Cite journal|last=Jacoby|first=Mitch|title=As-yet-unsynthesized superheavy atom should form a stable diatomic molecule with fluorine|journal=Chemical & Engineering News|year=2006|volume=84|issue=10|pages=19|doi=10.1021/cen-v084n010.p019a}}</ref> Other predicted oxidation states include +2, +4, and +6; +4 is expected to be the most usual oxidation state of unbihexium.<ref name="BFricke"/> The superactinides from unbipentium (element 125) to unbiennium (element 129) are predicted to exhibit a +6 oxidation state and form [[hexafluorides]], though 125F{{sub|6}} and 126F{{sub|6}} are predicted to be relatively weakly bound.<ref name="5gchem">{{cite journal|last1=Dongon|first1=J.P.|last2=Pyykkö|first2=P.|date=2017|title=Chemistry of the 5g elements. Relativistic calculations on hexafluorides|journal= Angewandte Chemie International Edition|volume=56|issue=34|pages=10132–10134|doi=10.1002/anie.201701609|pmid=28444891|s2cid=205400592 |url=https://hal-cea.archives-ouvertes.fr/cea-01515489/document}}</ref> The [[bond dissociation energies]] are expected to greatly increase at element 127 and even more so at element 129. This suggests a shift from strong ionic character in fluorides of element 125 to more covalent character, involving the 8p orbital, in fluorides of element 129. The bonding in these superactinide hexafluorides is mostly between the highest 8p subshell of the superactinide and the 2p subshell of fluorine, unlike how uranium uses its 5f and 6d orbitals for bonding in [[uranium hexafluoride]].<ref name=5gchem/> Despite the ability of early superactinides to reach high oxidation states, it has been calculated that the 5g electrons will be most difficult to ionize; the 125{{sup|6+}} and 126{{sup|7+}} ions are expected to bear a 5g{{sup|1}} configuration, similar to the 5f{{sup|1}} configuration of the Np{{sup|6+}} ion.<ref name="PT172"/><ref name=5gchem/> Similar behavior is observed in the low chemical activity of the 4f electrons in [[lanthanide]]s; this is a consequence of the 5g orbitals being small and deeply buried in the electron cloud.<ref name="PT172"/> The presence of electrons in g-orbitals, which do not exist in the ground state electron configuration of any currently known element, should allow presently unknown [[orbital hybridization|hybrid]] orbitals to form and influence the chemistry of the superactinides in new ways, although the absence of ''g'' electrons in known elements makes predicting superactinide chemistry more difficult.<ref name="Fricke"/> <div style="margin:0 auto; font-size:85%;"> :{| class="wikitable" |+ Some predicted compounds of the superactinides (X = a [[halogen]])<ref name="PT172"/><ref name=5gchem/><ref>{{cite journal |last=Makhyoun |first=M. A. |date=October 1988 |title=On the electronic structure of 5g<sup>1</sup> complexes of element 125: a quasi-relativistic MS-Xα study |journal=Journal de Chimie Physique et de Physico-Chimie Biologique |volume=85 |issue=10 |pages=917–24 |doi=10.1051/jcp/1988850917 |bibcode=1988JCP....85..917M }}</ref> ! ! 121 ! 122 ! 123 ! 124 ! 125 ! 126 ! 127 ! 128 ! 129 ! 132 ! 142 ! 143 ! 144 ! 145 ! 146 ! 148 ! 153 ! 154 ! 155 ! 156 ! 157 |- ! Compound | 121X<sub>3</sub> | 122X<sub>4</sub> | 123X<sub>5</sub> | 124X<sub>6</sub> | 125F<br/>125F<sub>6</sub><br/>{{chem|125O|2|2+}} | 126F<br/>126F<sub>6</sub><br/>126O<sub>4</sub> | 127F<sub>6</sub> | 128F<sub>6</sub> | 129F<br/>129F<sub>6</sub> | | 142X<sub>4</sub><br/>142X<sub>6</sub> | 143F<sub>6</sub> | 144X<sub>6</sub><br/>{{chem|144O|2|2+}}<br/>144F<sub>8</sub><br/>144O<sub>4</sub> | 145F<sub>6</sub> | | 148O<sub>6</sub> | | | | | |- ! Analogs | [[lanthanum|La]]X<sub>3</sub><br/>[[actinium|Ac]]X<sub>3</sub> | [[cerium|Ce]]X<sub>4</sub><br/>[[thorium|Th]]X<sub>4</sub> | | | {{chem|[[neptunium|Np]]O|2|2+}} | | | | | | [[thorium tetrafluoride|ThF<sub>4</sub>]] | | [[uranium hexafluoride|UF<sub>6</sub>]]<br/>[[uranyl|{{chem|UO|2|2+}}]]<br/>[[plutonium|Pu]]F<sub>8</sub><br/>PuO<sub>4</sub> | | | [[uranium hexoxide|UO<sub>6</sub>]] | | | | | |- ! Oxidation states | 3 | 4 | 5 | 6 | 1, 6, 7 | 1, 2, 4, 6, 8 | 6 | 6 | 1, 6 | 6 | 4, 6 | 6, 8 | 3, 4, 5, 6, 8 | 6 | 8 | 12 | 3 | 0, 2 | 3, 5 | 2 | 3 |} </div>{{clear}} In the later superactinides, the oxidation states should become lower. By element 132, the predominant most stable oxidation state will be only +6; this is further reduced to +3 and +4 by element 144, and at the end of the superactinide series it will be only +2 (and possibly even 0) because the 6f shell, which is being filled at that point, is deep inside the electron cloud and the 8s and 8p{{sub|1/2}} electrons are bound too strongly to be chemically active. The 5g shell should be filled at element 144 and the 6f shell at around element 154, and at this region of the superactinides the 8p{{sub|1/2}} electrons are bound so strongly that they are no longer active chemically, so that only a few electrons can participate in chemical reactions. Calculations by Fricke et al. predict that at element 154, the 6f shell is full and there are no d- or other electron [[wave function]]s outside the chemically inactive 8s and 8p<sub>1/2</sub> shells. This may cause element 154 to be rather [[reactivity (chemistry)|unreactive]] with [[noble gas]]-like properties.<ref name="Fricke"/><ref name=Haire/> Calculations by Pyykkö nonetheless expect that at element 155, the 6f shell is still chemically ionizable: 155{{sup|3+}} should have a full 6f shell, and the fourth ionization potential should be between those of [[terbium]] and [[dysprosium]], both of which are known in the +4 state.<ref name=PT172/> Similarly to the [[lanthanide contraction|lanthanide and actinide contractions]], there should be a superactinide contraction in the superactinide series where the [[ionic radius|ionic radii]] of the superactinides are smaller than expected. In the [[lanthanide]]s, the contraction is about 4.4 pm per element; in the [[actinide]]s, it is about 3 pm per element. The contraction is larger in the lanthanides than in the actinides due to the greater localization of the 4f wave function as compared to the 5f wave function. Comparisons with the wave functions of the outer electrons of the lanthanides, actinides, and superactinides lead to a prediction of a contraction of about 2 pm per element in the superactinides; although this is smaller than the contractions in the lanthanides and actinides, its total effect is larger due to the fact that 32 electrons are filled in the deeply buried 5g and 6f shells, instead of just 14 electrons being filled in the 4f and 5f shells in the lanthanides and actinides, respectively.<ref name="Fricke"/> [[Pekka Pyykkö]] divides these superactinides into three series: a 5g series (elements 121 to 138), an 8p<sub>1/2</sub> series (elements 139 to 140), and a 6f series (elements 141 to 155), also noting that there would be a great deal of overlapping between energy levels and that the 6f, 7d, or 8p<sub>1/2</sub> orbitals could well also be occupied in the early superactinide atoms or ions. He also expects that they would behave more like "superlanthanides", in the sense that the 5g electrons would mostly be chemically inactive, similarly to how only one or two 4f electrons in each lanthanide are ever ionized in chemical compounds. He also predicted that the possible oxidation states of the superactinides might rise very high in the 6f series, to values such as +12 in element 148.<ref name="PT172"/> Andrey Kulsha has called the elements 121 to 156 "ultransition" elements and has proposed to split them into two series of eighteen each, one from elements 121 to 138 and another from elements 139 to 156. The first would be analogous to the lanthanides, with oxidation states mainly ranging from +4 to +6, as the filling of the 5g shell dominates and neighbouring elements are very similar to each other, creating an analogy to [[uranium]], [[neptunium]], and [[plutonium]]. The second would be analogous to the actinides: at the beginning (around elements in the 140s) very high oxidation states would be expected as the 6f shell rises above the 7d one, but after that the typical oxidation states would lower and in elements in the 150s onwards the 8p{{sub|1/2}} electrons would stop being chemically active. Because the two rows are separated by the addition of a complete 5g{{sup|18}} subshell, they could be considered analogues of each other as well.<ref name=primefan/><ref name=sicius/> As an example from the late superactinides, element 156 is expected to exhibit mainly the +2 oxidation state, on account of its electron configuration with easily removed 7d{{sup|2}} electrons over a stable [Og]5g{{sup|18}}6f{{sup|14}}8s{{sup|2}}8p{{su|p=2|b=1/2}} core. It can thus be considered a heavier congener of [[nobelium]], which likewise has a pair of easily removed 7s{{sup|2}} electrons over a stable [Rn]5f{{sup|14}} core, and is usually in the +2 state (strong oxidisers are required to obtain nobelium in the +3 state).<ref name=primefan/> Its first ionization energy should be about 400 kJ/mol and its metallic radius approximately 170 picometers. With a relative atomic mass of around 445 u,<ref name=Fricke/> it should be a very heavy metal with a density of around 26 g/cm<sup>3</sup>. ====Elements 157 to 166==== The 7d transition metals in period 8 are expected to be elements 157 to 166. Although the 8s and 8p<sub>1/2</sub> electrons are bound so strongly in these elements that they should not be able to take part in any chemical reactions, the 9s and 9p<sub>1/2</sub> levels are expected to be readily available for hybridization.<ref name="Fricke"/><ref name=Haire/> These 7d elements should be similar to the 4d elements [[yttrium]] through [[cadmium]].<ref name=primefan/> In particular, element 164 with a 7d<sup>10</sup>9s<sup>0</sup> electron configuration shows clear analogies with [[palladium]] with its 4d<sup>10</sup>5s<sup>0</sup> electron configuration.<ref name=BFricke/> The noble metals of this series of transition metals are not expected to be as noble as their lighter homologues, due to the absence of an outer ''s'' shell for shielding and also because the 7d shell is strongly split into two subshells due to relativistic effects. This causes the first ionization energies of the 7d transition metals to be smaller than those of their lighter congeners.<ref name="Fricke"/><ref name=Haire/><ref name="BFricke"/> Theoretical interest in the chemistry of unhexquadium is largely motivated by theoretical predictions that it, especially the isotopes <sup>472</sup>164 and <sup>482</sup>164 (with 164 [[proton]]s and 308 or 318 [[neutron]]s), would be at the center of a hypothetical second [[island of stability]] (the first being centered on [[copernicium]], particularly the isotopes <sup>291</sup>Cn, <sup>293</sup>Cn, and <sup>296</sup>Cn which are expected to have half-lives of centuries or millennia).<ref name=magickoura/><ref name="Kratz"> {{cite conference |last1=Kratz |first1=J. V. |date=5 September 2011 |title=The Impact of Superheavy Elements on the Chemical and Physical Sciences |url=http://tan11.jinr.ru/pdf/06_Sep/S_1/02_Kratz.pdf |conference=4th International Conference on the Chemistry and Physics of the Transactinide Elements |access-date=27 August 2013 }}</ref><ref name="eurekalert.org">{{cite web|url=http://www.eurekalert.org/pub_releases/2008-04/acs-nse031108.php|title=Nuclear scientists eye future landfall on a second 'island of stability'|date=6 April 2008|website=EurekAlert!|access-date=2015-12-17}}</ref><ref name="link.springer.com">{{cite journal | doi = 10.1007/BF01406719 | volume = 228 | issue = 5 | title = Investigation of the stability of superheavy nuclei aroundZ=114 andZ=164 | journal = Zeitschrift für Physik | pages = 371–386 | bibcode = 1969ZPhy..228..371G | year = 1969 | last1 = Grumann | first1 = Jens | last2 = Mosel | first2 = Ulrich | last3 = Fink | first3 = Bernd | last4 = Greiner | first4 = Walter | s2cid = 120251297 }}</ref> Calculations predict that the 7d electrons of element 164 (unhexquadium) should participate very readily in chemical reactions, so that it should be able to show stable +6 and +4 oxidation states in addition to the normal +2 state in [[aqueous solution]]s with strong [[ligand]]s. Element 164 should thus be able to form compounds like 164([[carbonyl|CO]])<sub>4</sub>, 164([[phosphorus trifluoride|PF<sub>3</sub>]])<sub>4</sub> (both [[tetrahedral molecular geometry|tetrahedral]] like the corresponding palladium compounds), and {{chem|164([[cyanide|CN]])|2|2-}} ([[linear molecular geometry|linear]]), which is very different behavior from that of [[lead]], which element 164 would be a heavier [[Homologous series|homologue]] of if not for relativistic effects. Nevertheless, the divalent state would be the main one in aqueous solution (although the +4 and +6 states would be possible with stronger ligands), and unhexquadium(II) should behave more similarly to lead than unhexquadium(IV) and unhexquadium(VI).<ref name=Haire/><ref name="BFricke">{{Cite journal |last1=Fricke |first1=Burkhard |year=1975 |title=Superheavy elements: a prediction of their chemical and physical properties |journal=Recent Impact of Physics on Inorganic Chemistry |volume=21 |pages=[https://archive.org/details/recentimpactofph0000unse/page/89 89–144] |doi=10.1007/BFb0116498 |url=https://archive.org/details/recentimpactofph0000unse/page/89 |access-date=4 October 2013 |series=Structure and Bonding |isbn=978-3-540-07109-9 }}</ref> Element 164 is expected to be a soft [[Lewis acid]] and have Ahrlands softness parameter close to 4 [[electronvolt|eV]]. It should be at most moderately reactive, having a first ionization energy that should be around 685 kJ/mol, comparable to that of [[molybdenum]].<ref name="Fricke"/><ref name="BFricke"/> Due to the [[lanthanide contraction|lanthanide, actinide, and superactinide contractions]], element 164 should have a metallic radius of only 158 [[picometer|pm]], very close to that of the much lighter [[magnesium]], despite its expected atomic weight of around 474 [[atomic mass unit|u]] which is about 19.5 times the atomic weight of magnesium.<ref name="Fricke"/> This small radius and high weight cause it to be expected to have an extremely high density of around 46 g·cm<sup>−3</sup>, over twice that of [[osmium]], currently the most dense element known, at 22.61 g·cm<sup>−3</sup>; element 164 should be the second most dense element in the first 172 elements in the periodic table, with only its neighbor unhextrium (element 163) being more dense (at 47 g·cm<sup>−3</sup>).<ref name="Fricke"/> Metallic element 164 should have a very large cohesive energy ([[enthalpy]] of crystallization) due to its [[Covalent bond|covalent]] bonds, most probably resulting in a high melting point. In the metallic state, element 164 should be quite noble and analogous to palladium and [[platinum]]. Fricke et al. suggested some formal similarities to [[oganesson]], as both elements have closed-shell configurations and similar ionisation energies, although they note that while oganesson would be a very bad noble gas, element 164 would be a good noble metal.<ref name="BFricke"/> Elements 165 (unhexpentium) and 166 (unhexhexium), the last two 7d metals, should behave similarly to [[alkali metal|alkali]] and [[alkaline earth metal]]s when in the +1 and +2 oxidation states, respectively. The 9s electrons should have ionization energies comparable to those of the 3s electrons of [[sodium]] and [[magnesium]], due to relativistic effects causing the 9s electrons to be much more strongly bound than non-relativistic calculations would predict. Elements 165 and 166 should normally exhibit the +1 and +2 oxidation states, respectively, although the ionization energies of the 7d electrons are low enough to allow higher oxidation states like +3 for element 165. The oxidation state +4 for element 166 is less likely, creating a situation similar to the lighter elements in groups 11 and 12 (particularly [[gold]] and [[mercury (element)|mercury]]).<ref name="Fricke"/><ref name=Haire/> As with mercury but not copernicium, ionization of element 166 to 166<sup>2+</sup> is expected to result in a 7d<sup>10</sup> configuration corresponding to the loss of the s-electrons but not the d-electrons, making it more analogous to the lighter "less relativistic" group 12 elements zinc, cadmium, and mercury.<ref name=PT172/> <div style="float: center; margin: 1px; font-size:85%;"> :{| class="wikitable" |+ Some predicted properties of elements 156–166<br/>The metallic radii and densities are first approximations.<ref name="Fricke"/><ref name="PT172"/><ref name=Haire/><br/>Most analogous group is given first, followed by other similar groups.<ref name="BFricke"/> ! Property ! 156 ! 157 ! 158 ! 159 ! 160 ! 161 ! 162 ! 163 ! 164 ! 165 ! 166 |- ! [[Standard atomic weight]] | [445] | [448] | [452] | [456] | [459] | [463] | [466] | [470] | [474] | [477] | [481] |- ! [[Periodic table group|Group]] | [[ytterbium|Yb]] group | [[group 3 element|3]] | [[group 4 element|4]] | [[group 5 element|5]] | [[group 6 element|6]] | [[group 7 element|7]] | [[group 8 element|8]] | [[group 9 element|9]] | [[group 10 element|10]] | [[group 11 element|11]]<br/>(1) | [[group 12 element|12]]<br/>(2) |- ! Valence [[electron configuration]] | 7d<sup>2</sup> | 7d<sup>3</sup> | 7d<sup>4</sup> | 7d<sup>5</sup> | 7d<sup>6</sup> | 7d<sup>7</sup> | 7d<sup>8</sup> | 7d<sup>9</sup> | 7d<sup>10</sup> | 7d<sup>10</sup> 9s<sup>1</sup> | 7d<sup>10</sup> 9s<sup>2</sup> |- ! Stable [[oxidation state]]s | '''2''' | '''3''' | '''4''' | '''1''', '''5''' | '''2''', '''6''' | '''3''', '''7''' | '''4''', '''8''' | '''5''' | '''0''', '''2''', '''4''', '''6''' | '''1''', '''3''' | '''2''' |- ! First [[ionization energy]] | 400 kJ/mol | 450 kJ/mol | 520 kJ/mol | 340 kJ/mol | 420 kJ/mol | 470 kJ/mol | 560 kJ/mol | 620 kJ/mol | 690 kJ/mol | 520 kJ/mol | 630 kJ/mol |- ! [[Metallic radius]] | 170 pm | 163 pm | 157 pm | 152 pm | 148 pm | 148 pm | 149 pm | 152 pm | 158 pm | 250 pm | 200 pm |- ! [[Density]] | 26 g/cm<sup>3</sup> | 28 g/cm<sup>3</sup> | 30 g/cm<sup>3</sup> | 33 g/cm<sup>3</sup> | 36 g/cm<sup>3</sup> | 40 g/cm<sup>3</sup> | 45 g/cm<sup>3</sup> | 47 g/cm<sup>3</sup> | 46 g/cm<sup>3</sup> | 7 g/cm<sup>3</sup> | 11 g/cm<sup>3</sup> |} </div> ====Elements 167 to 172==== The next six elements on the periodic table are expected to be the last main-group elements in their period,<ref name="PT172"/> and are likely to be similar to the 5p elements [[indium]] through [[xenon]].<ref name=primefan/> In elements 167 to 172, the 9p<sub>1/2</sub> and 8p<sub>3/2</sub> shells will be filled. Their energy [[eigenvalue]]s are so close together that they behave as one combined p-subshell, similar to the non-relativistic 2p and 3p subshells. Thus, the [[inert-pair effect]] does not occur and the most common oxidation states of elements 167 to 170 are expected to be +3, +4, +5, and +6, respectively. Element 171 (unseptunium) is expected to show some similarities to the [[halogen]]s, showing various oxidation states ranging from −1 to +7, although its physical properties are expected to be closer to that of a metal. Its electron affinity is expected to be 3.0 [[electronvolt|eV]], allowing it to form H171, analogous to a [[hydrogen halide]]. The 171<sup>−</sup> ion is expected to be a [[HSAB|soft base]], comparable to [[iodide]] (I<sup>−</sup>). Element 172 (unseptbium) is expected to be a [[noble gas]] with chemical behaviour similar to that of xenon, as their ionization energies should be very similar (Xe, 1170.4 kJ/mol; element 172, 1090 kJ/mol). The only main difference between them is that element 172, unlike xenon, is expected to be a [[liquid]] or a [[solid]] at [[standard temperature and pressure]] due to its much higher atomic weight.<ref name="Fricke"/> Unseptbium is expected to be a strong [[Lewis acid]], forming fluorides and oxides, similarly to its lighter congener xenon.<ref name="BFricke"/> Because of some analogy of elements 165–172 to periods 2 and 3, Fricke et al. considered them to form a ninth period of the periodic table, while the eighth period was taken by them to end at the noble metal element 164. This ninth period would be similar to the second and third period in having no transition metals.<ref name="BFricke"/> That being said, the analogy is incomplete for elements 165 and 166; although they do start a new s-shell (9s), this is above a d-shell, making them chemically more similar to groups 11 and 12.<ref name=actrev/> <div style="float: center; margin: 1px; font-size:85%;"> :{| class="wikitable" |+ Some predicted properties of elements 167–172<br/>The metallic or covalent radii and densities are first approximations.<ref name="Fricke"/><ref name=Haire/><ref name="BFricke"/> ! Property ! 167 ! 168 ! 169 ! 170 ! 171 ! 172 |- ! [[Standard atomic weight]] | [485] | [489] | [493] | [496] | [500] | [504] |- ! [[Periodic table group|Group]] | [[boron group|13]] | [[carbon group|14]] | [[pnictogen|15]] | [[chalcogen|16]] | [[halogen|17]] | [[noble gas|18]] |- ! Valence [[electron configuration]] | 9s<sup>2</sup> 9p<sup>1</sup> | 9s<sup>2</sup> 9p<sup>2</sup> | 9s<sup>2</sup> 9p<sup>2</sup> 8p<sup>1</sup> | 9s<sup>2</sup> 9p<sup>2</sup> 8p<sup>2</sup> | 9s<sup>2</sup> 9p<sup>2</sup> 8p<sup>3</sup> | 9s<sup>2</sup> 9p<sup>2</sup> 8p<sup>4</sup> |- ! Stable [[oxidation state]]s | '''3''' | '''4''' | '''5''' | '''6''' | '''−1''', '''3''', '''7''' | '''0''', '''4''', '''6''', '''8''' |- ! First [[ionization energy]] | 620 kJ/mol | 720 kJ/mol | 800 kJ/mol | 890 kJ/mol | 984 kJ/mol | 1090 kJ/mol |- ! [[Metallic radius|Metallic]] or [[covalent radius]] | 190 pm | 180 pm | 175 pm | 170 pm | 165 pm | 220 pm |- ! [[Density]] | 17 g/cm<sup>3</sup> | 19 g/cm<sup>3</sup> | 18 g/cm<sup>3</sup> | 17 g/cm<sup>3</sup> | 16 g/cm<sup>3</sup> | 9 g/cm<sup>3</sup> |} </div> ====Beyond element 172==== Beyond element 172, there is the potential to fill the 6g, 7f, 8d, 10s, 10p<sub>1/2</sub>, and perhaps 6h<sub>11/2</sub> shells. These electrons would be very loosely bound, potentially rendering extremely high oxidation states reachable, though the electrons would become more tightly bound as the ionic charge rises. Thus, there will probably be another very long transition series, like the superactinides.<ref name="BFricke"/> In element 173 (unsepttrium), the outermost electron might enter the 6g<sub>7/2</sub>, 9p<sub>3/2</sub>, or 10s subshells. Because spin–orbit interactions would create a very large energy gap between these and the 8p<sub>3/2</sub> subshell, this outermost electron is expected to be very loosely bound and very easily lost to form a 173<sup>+</sup> cation. As a result, element 173 is expected to behave chemically like an alkali metal, and one that might be far more reactive than even [[caesium]] (francium and element 119 being less reactive than caesium due to relativistic effects):<ref name="BFricke1977">{{cite journal |last1=Fricke |first1=Burkhard |author-link=Burkhard Fricke |year=1977 |title=Dirac–Fock–Slater calculations for the elements Z = 100, fermium, to Z = 173 |url=http://kobra.bibliothek.uni-kassel.de/bitstream/urn:nbn:de:hebis:34-2008071622807/1/Fricke_Dirac_1977.pdf |journal=Recent Impact of Physics on Inorganic Chemistry |volume=19 |pages=83–192 |bibcode=1977ADNDT..19...83F |doi=10.1016/0092-640X(77)90010-9 |access-date=25 February 2016}}</ref><ref name=primefan>{{cite book |editor-last=Kolevich |editor-first=T. A. |last1=Kulsha |first1=Andrey |chapter=Есть ли граница у таблицы Менделеева? |trans-chapter=Is there a boundary to the Mendeleev table? |date=2011 |title=Удивительный мир веществ и их превращений |trans-title=The wonderful world of substances and their transformations |url=http://www.primefan.ru/stuff/chem/ptable/ptable.pdf |location=Minsk |publisher=Национальный институт образования (National Institute of Education) |pages=5–19 |isbn=978-985-465-920-6 |language=ru |access-date=8 September 2018}}</ref> the calculated ionisation energy for element 173 is 3.070 eV,<ref name=eliav2023/> compared to the experimentally known 3.894 eV for caesium. Element 174 (unseptquadium) may add an 8d electron and form a closed-shell 174<sup>2+</sup> cation; its calculated ionisation energy is 3.614 eV.<ref name=eliav2023/> Element 184 (unoctquadium) was significantly targeted in early predictions, as it was originally speculated that 184 would be a proton magic number: it is predicted to have an electron configuration of [172] 6g<sup>5</sup> 7f<sup>4</sup> 8d<sup>3</sup>, with at least the 7f and 8d electrons chemically active. Its chemical behaviour is expected to be similar to [[uranium]] and [[neptunium]], as further ionisation past the +6 state (corresponding to removal of the 6g electrons) is likely to be unprofitable; the +4 state should be most common in aqueous solution, with +5 and +6 reachable in solid compounds.<ref name="Fricke"/><ref name="BFricke"/><ref name=Penneman>{{cite journal |last1=Penneman |first1=R. A. |last2=Mann |first2=J. B. |last3=Jørgensen |first3=C. K. |date=February 1971 |title=Speculations on the chemistry of superheavy elements such as Z = 164 |journal=Chemical Physics Letters |volume=8 |issue=4 |pages=321–326 |doi=10.1016/0009-2614(71)80054-4 |bibcode=1971CPL.....8..321P }}</ref> ===End of the periodic table=== The number of physically possible elements is unknown. A low estimate is that the periodic table may end soon after the [[island of stability]],<ref name=EB>{{cite encyclopedia|last1=Seaborg|first1=Glenn T.|url=https://www.britannica.com/EBchecked/topic/603220/transuranium-element|title=transuranium element (chemical element)|encyclopedia=Encyclopædia Britannica|date=c. 2006|access-date=2010-03-16}}</ref> which is expected to center on ''Z'' = 126, as the extension of the periodic and [[nuclide]] tables is restricted by the proton and the neutron [[Nuclear drip line|drip lines]] and stability toward alpha decay and spontaneous fission.<ref>{{cite journal | first1=S. |last1=Cwiok|first2=P.-H.|last2=Heenen |first3=W.|last3=Nazarewicz |year=2005|title=Shape coexistence and triaxiality in the superheavy nuclei|journal=Nature|volume=433|bibcode = 2005Natur.433..705C |doi = 10.1038/nature03336 | issue=7027 | pmid=15716943 | pages=705–9|s2cid=4368001}}</ref> One calculation by Y. Gambhir ''et al.'', analyzing [[nuclear binding energy]] and stability in various decay channels, suggests a limit to the existence of bound nuclei at ''Z'' = 146.<ref name=limit146>{{cite journal|last1=Gambhir|first1=Y. K.|last2=Bhagwat|first2=A.|last3=Gupta|first3=M.|title=The highest limiting Z in the extended periodic table|date=2015|journal=Journal of Physics G: Nuclear and Particle Physics|volume=42|issue=12|pages=125105|doi=10.1088/0954-3899/42/12/125105|url= https://www.researchgate.net/publication/284213926|bibcode=2015JPhG...42l5105G}}</ref> Other predictions of an end to the periodic table include ''Z'' = 128 ([[John Emsley]]) and ''Z'' = 155 (Albert Khazan).<ref name="emsley"/> ====Elements above the atomic number 137==== It is a "folk legend" among physicists that [[Richard Feynman]] suggested that neutral atoms could not exist for atomic numbers greater than ''Z'' = 137, on the grounds that the [[Theory of relativity|relativistic]] [[Dirac equation]] predicts that the ground-state energy of the innermost electron in such an atom would be an [[imaginary number]]. Here, the number 137 arises as the inverse of the [[fine-structure constant]]. By this argument, neutral atoms cannot exist beyond atomic number 137, and therefore a periodic table of elements based on electron orbitals breaks down at this point. However, this argument presumes that the atomic nucleus is pointlike. A more accurate calculation must take into account the small, but nonzero, size of the nucleus, which is predicted to push the limit further to ''Z'' ≈ 173.<ref name="rsc">{{cite web |url=https://www.chemistryworld.com/opinion/column-the-crucible/3005076.article |title=Would element 137 really spell the end of the periodic table? Philip Ball examines the evidence|author=Philip Ball |date=November 2010 |website=[[Chemistry World]]|publisher=[[Royal Society of Chemistry]] |access-date=2012-09-30}}</ref> =====Bohr model===== The [[Bohr model]] exhibits difficulty for atoms with atomic number greater than 137, for the speed of an electron in a [[Atomic orbital|1s electron orbital]], ''v'', is given by :<math>v = Z \alpha c \approx \frac{Z c}{137.04}</math> where ''Z'' is the [[atomic number]], and ''α'' is the [[fine-structure constant]], a measure of the strength of electromagnetic interactions.<ref>{{cite book|first1=R. |last1=Eisberg|first2= R.|last2= Resnick|year=1985|title=Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles|url=https://archive.org/details/quantumphysicsof00eisb |url-access=registration |publisher=[[John Wiley & Sons|Wiley]]|isbn=9780471873730}}</ref> Under this approximation, any element with an atomic number of greater than 137 would require 1s electrons to be traveling faster than ''c'', the [[speed of light]]. Hence, the non-relativistic Bohr model is inaccurate when applied to such an element. =====Relativistic Dirac equation===== [[File:1s negative continuum.svg|thumb|right|540px|Energy eigenvalues for the 1s, 2s, 2p<sub>1/2</sub> and 2p<sub>3/2</sub> shells from solutions of the [[Dirac equation]] (taking into account the finite size of the nucleus) for ''Z'' = 135–175 (–·–), for the Thomas-Fermi potential (—) and for ''Z'' = 160–170 with the self-consistent potential (---)<ref name=Fricke/>]] The [[Theory of relativity|relativistic]] [[Dirac equation]] gives the ground state energy as :<math>E=\frac{m c^2}{\sqrt{1+\dfrac{Z^2 \alpha^2}{\bigg({n-\left(j+\frac12\right)+\sqrt{\left(j+\frac12\right)^2-Z^ 2\alpha^2}\bigg)}^2}}},</math> where ''m'' is the rest mass of the electron.<ref>{{cite web |title=Solution of the Dirac Equation for Hydrogen |url=https://quantummechanics.ucsd.edu/ph130a/130_notes/node501.html}}</ref> For ''Z'' > 137, the wave function of the Dirac ground state is oscillatory, rather than bound, and there is no gap between the positive and negative energy spectra, as in the [[Klein paradox]].<ref>{{cite book|first1=J. D.|last1= Bjorken|first2=S. D.|last2= Drell|year=1964|title=Relativistic Quantum Mechanics|url=https://archive.org/details/relativisticquan0000bjor|url-access=registration|publisher=[[McGraw-Hill]]}}</ref> More accurate calculations taking into account the effects of the finite size of the nucleus indicate that the binding energy first exceeds 2''mc''<sup>2</sup> for ''Z'' > ''Z''<sub>cr</sub> probably between 168 and 172.<ref name=gamowstates/> For ''Z'' > ''Z''<sub>cr</sub>, if the innermost orbital (1s) is not filled, the electric field of the nucleus will [[pair production|pull an electron out of the vacuum]], resulting in the spontaneous emission of a [[positron]].<ref>{{cite journal|first1=W. |last1=Greiner|first2= S. |last2=Schramm |year=2008|title=Resource Letter QEDV-1: The QED vacuum |journal=[[American Journal of Physics]] |volume=76 |issue=6|pages=509 |doi=10.1119/1.2820395|bibcode=2008AmJPh..76..509G}}, and references therein</ref><ref>{{cite journal|last1=Wang|first1=Yang|last2=Wong|first2=Dillon|last3=Shytov|first3=Andrey V.|last4=Brar|first4=Victor W.|last5=Choi|first5=Sangkook|last6=Wu|first6=Qiong|last7=Tsai|first7=Hsin-Zon|last8=Regan|first8=William|last9=Zettl|first9=Alex|author9-link=Alex Zettl|last10=Kawakami|first10=Roland K.|last11=Louie|first11=Steven G.|last12=Levitov|first12=Leonid S.|last13=Crommie|first13=Michael F.|title=Observing Atomic Collapse Resonances in Artificial Nuclei on Graphene|journal=Science|date=May 10, 2013|volume=340|issue=6133|pages=734–737|doi=10.1126/science.1234320|arxiv = 1510.02890 |bibcode = 2013Sci...340..734W|pmid=23470728|s2cid=29384402}}</ref> This diving of the 1s subshell into the negative continuum has often been taken to constitute an "end" to the periodic table,<ref name=PT172/><ref name="rsc"/><ref>{{Cite journal|last1=Indelicato|first1=Paul|last2=Bieroń|first2=Jacek|last3=Jönsson|first3=Per|date=2011-06-01|title=Are MCDF calculations 101% correct in the super-heavy elements range?|url=https://dspace.mah.se/handle/2043/12984|journal=Theoretical Chemistry Accounts|language=en|volume=129|issue=3–5|pages=495–505|doi=10.1007/s00214-010-0887-3|issn=1432-881X|hdl=2043/12984|s2cid=54680128|hdl-access=free}}</ref> but in fact it does not impose such a limit, as such resonances can be interpreted as [[Gamow state]]s. Nonetheless, the accurate description of such states in a multi-electron system, needed to extend calculations and the periodic table past ''Z''<sub>cr</sub> ≈ 172, are still open problems.<ref name=gamowstates>{{cite journal |last1=Smits |first1=O. R. |last2=Indelicato |first2=P. |first3=W. |last3=Nazarewicz |first4=M. |last4=Piibeleht |first5=P. |last5=Schwerdtfeger |date=2023 |title=Pushing the limits of the periodic table—A review on atomic relativistic electronic structure theory and calculations for the superheavy elements |url= |journal=Physics Reports |volume=1035 |issue= |pages=1–57 |doi=10.1016/j.physrep.2023.09.004 |access-date=|arxiv=2301.02553 |bibcode=2023PhR..1035....1S }}</ref> Atoms with atomic numbers above ''Z''<sub>cr</sub> ≈ 172 have been termed ''supercritical'' atoms. Supercritical atoms cannot be totally ionised because their 1s subshell would be filled by spontaneous pair creation in which an electron-positron pair is created from the negative continuum, with the electron being bound and the positron escaping. However, the strong field around the atomic nucleus is restricted to a very small region of space, so that the [[Pauli exclusion principle]] forbids further spontaneous pair creation once the subshells that have dived into the negative continuum are filled. Elements 173–184 have been termed ''weakly supercritical'' atoms as for them only the 1s shell has dived into the negative continuum; the 2p<sub>1/2</sub> shell is expected to join around element 185 and the 2s shell around element 245. Experiments have so far not succeeded in detecting spontaneous pair creation from assembling supercritical charges through the collision of heavy nuclei (e.g. colliding lead with uranium to momentarily give an effective ''Z'' of 174; uranium with uranium gives effective ''Z'' = 184 and uranium with californium gives effective ''Z'' = 190).<ref>{{cite book|last1=Reinhardt|first1=Joachim|title = Nuclear Physics: Present and Future|pages=195–210|last2=Greiner|first2=Walter|doi=10.1007/978-3-319-10199-6_19|date=2015|chapter=Probing Supercritical Fields with Real and with Artificial Nuclei|isbn=978-3-319-10198-9}}</ref> Even though passing ''Z''<sub>cr</sub> does not mean elements can no longer exist, the increasing concentration of the 1s density close to the nucleus would likely make these electrons more vulnerable to [[electron capture|''K'' electron capture]] as ''Z''<sub>cr</sub> is approached. For such heavy elements, these 1s electrons would likely spend a significant fraction of time so close to the nucleus that they are actually inside it. This may pose another limit to the periodic table.<ref name=colloq>{{cite journal |title=Colloquium: Superheavy elements: Oganesson and beyond |first1=S. A. |last1=Giuliani |first2=Z. |last2=Matheson |first3=W. |last3=Nazarewicz |first4=E. |last4=Olsen |first5=P.-G. |last5=Reinhard |first6=J. |last6=Sadhukhan |first7=B. |last7=Schtruempf |first8=N. |last8=Schunck |first9=P. |last9=Schwerdtfeger |date=2019 |journal=Reviews of Modern Physics |volume=91 |issue=1 |pages=011001-1–011001-25 |doi=10.1103/RevModPhys.91.011001|bibcode=2019RvMP...91a1001G |s2cid=126906074 |doi-access=free }}</ref> Because of the factor of ''m'', [[muonic atom]]s become supercritical at a much larger atomic number of around 2200, as [[muon]]s are about 207 times as heavy as electrons.<ref name=gamowstates/> =====Quark matter===== {{main|Continent of stability|QCD matter}} It has also been posited that in the region beyond ''A'' > 300, an entire "[[continent of stability]]" consisting of a hypothetical phase of stable [[quark matter]], comprising freely flowing [[up quark|up]] and [[down quark|down]] quarks rather than [[quark]]s bound into protons and neutrons, may exist. Such a form of matter is theorized to be a ground state of [[baryonic matter]] with a greater binding energy per [[baryon]] than [[nuclear matter]], favoring the decay of nuclear matter beyond this mass threshold into quark matter. If this state of matter exists, it could possibly be synthesized in the same fusion reactions leading to normal superheavy nuclei, and would be stabilized against fission as a consequence of its stronger binding that is enough to overcome Coulomb repulsion.<ref name="udQM">{{cite journal |last1=Holdom |first1=B. |last2=Ren |first2=J. |last3=Zhang |first3=C. |title=Quark matter may not be strange |date=2018 |journal=Physical Review Letters |volume=120 |issue=1 |pages=222001-1–222001-6 <!-- Deny Citation Bot-->|doi=10.1103/PhysRevLett.120.222001|pmid=29906186 |arxiv=1707.06610 |bibcode=2018PhRvL.120v2001H |s2cid=49216916 }}</ref> Calculations published in 2020<ref name=udQMnew>{{cite journal |last1=Cheng-Jun |first1=Xia |last2=She-Sheng |first2=Xue |last3=Ren-Xin |first3=Xu |last4=Shan-Gui |first4=Zhou |title=Supercritically charged objects and electron-positron pair creation |doi=10.1103/PhysRevD.101.103031 |journal=Physical Review D |year=2020 |volume=101 |issue=10 |pages=103031|arxiv=2001.03531 |bibcode=2020PhRvD.101j3031X |s2cid=210157134 }}</ref> suggest stability of up-down quark matter (udQM) nuggets against conventional nuclei beyond ''A'' ~ 266, and also show that udQM nuggets become supercritical earlier (''Z''<sub>cr</sub> ~ 163, ''A'' ~ 609) than conventional nuclei (''Z''<sub>cr</sub> ~ 177, ''A'' ~ 480). ===Nuclear properties=== {{multiple image | direction =vertical | width = 540 | image1 = Island of Stability derived from Zagrebaev.svg | image2 = Superheavy decay modes predicted.png | footer = Predicted half-lives (top) and decay modes (bottom) of superheavy nuclei. The line of synthesized proton-rich nuclei is expected to be broken soon after ''Z'' = 120, because of half-lives shorter than 1 microsecond from ''Z'' = [[unbiunium|121]], the increasing contribution of spontaneous fission instead of alpha decay from ''Z'' = [[unbibium|122]] onward until it dominates from ''Z'' = 125, and the proton [[nuclear drip line|drip line]] around ''Z'' = 130. The white rings denote the expected location of the island of stability; the two squares outlined in white denote <sup>291</sup>[[copernicium|Cn]] and <sup>293</sup>Cn, predicted to be the longest-lived nuclides on the island with half-lives of centuries or millennia.<ref name=Karpov/> The black square near the bottom of the second picture is [[uranium-238]], the heaviest confirmed [[primordial nuclide]] (a nuclide stable enough to have survived from the Earth's formation to the present day). }} ====Magic numbers and the island of stability==== The stability of nuclei decreases greatly with the increase in atomic number after [[curium]], element 96, so that all isotopes with an atomic number above [[mendelevium|101]] [[radioactive decay|decay radioactively]] with a [[half-life]] under a day. No elements with [[atomic number]]s above 82 (after [[lead]]) have stable isotopes.<ref>{{cite journal|last = Marcillac|first = Pierre de |author2= Noël Coron|author3= Gérard Dambier|author4= Jacques Leblanc|author5= Jean-Pierre Moalic|date=April 2003|title = Experimental detection of α-particles from the radioactive decay of natural bismuth|journal = Nature|volume = 422|pages = 876–878|pmid=12712201|doi = 10.1038/nature01541|issue = 6934|bibcode = 2003Natur.422..876D|s2cid = 4415582 }}</ref> Nevertheless, because of [[magic number (physics)|reasons]] not very well understood yet, there is a slight increased nuclear stability around atomic numbers [[darmstadtium|110]]–[[flerovium|114]], which leads to the appearance of what is known in nuclear physics as the "[[island of stability]]". This concept, proposed by [[University of California, Berkeley|University of California]] professor [[Glenn Seaborg]], explains why [[superheavy element]]s last longer than predicted.<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> Calculations according to the [[Hartree–Fock method|Hartree–Fock–Bogoliubov method]] using the non-relativistic [[Skyrme interaction]] have proposed ''Z'' = 126 as a [[nuclear shell model|closed proton shell]]. In this region of the periodic table, ''N'' = 184, ''N'' = 196, and ''N'' = 228 have been suggested as closed neutron shells. Therefore, the isotopes of most interest are <sup>310</sup>126, <sup>322</sup>126, and <sup>354</sup>126, for these might be considerably longer-lived than other isotopes. Element 126, having a [[magic number (physics)|magic number]] of [[proton]]s, is predicted to be more stable than other elements in this region, and may have [[nuclear isomer]]s with very long [[half-life|half-lives]].<ref name="emsley2"/> It is also possible that the [[island of stability]] is instead centered at <sup>306</sup>[[unbibium|122]], which may be spherical and [[doubly magic]].<ref name="Kratz"/> Probably, the island of stability occurs around ''Z'' = 114–126 and ''N'' = 184, with lifetimes probably around hours to days. Beyond the shell closure at ''N'' = 184, spontaneous fission lifetimes should drastically drop below 10<sup>−15</sup> seconds – too short for a nucleus to obtain an electron cloud and participate in any chemistry. That being said, such lifetimes are very model-dependent, and predictions range across many orders of magnitude.<ref name=gamowstates/> Taking nuclear deformation and relativistic effects into account, an analysis of single-particle levels predicts new magic numbers for superheavy nuclei at ''Z'' = 126, 138, 154, and 164 and ''N'' = 228, 308, and 318.<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|access-date=2018-12-07}}</ref><ref name=magickoura>{{cite journal|last1=Koura|first1=H.|last2=Chiba|first2=S.|date=2013|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|issue=1|pages=014201|url=https://www.researchgate.net/publication/258799250 |doi=10.7566/JPSJ.82.014201|bibcode=2013JPSJ...82a4201K}}</ref> Therefore, in addition to the island of stability centered at <sup>291</sup>Cn, <sup>293</sup>Cn,<ref name=Zagrebaev/> and <sup>298</sup>Fl, further islands of stability may exist around the doubly magic <sup>354</sup>126 as well as <sup>472</sup>164 or <sup>482</sup>164.<ref name="eurekalert.org"/><ref name="link.springer.com"/> These nuclei are predicted to be [[beta-decay stable isobars|beta-stable]] and decay by alpha emission or spontaneous fission with relatively long half-lives, and confer additional stability on neighboring ''N'' = 228 [[isotone]]s and elements 152–168, respectively.<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|url=http://tan11.jinr.ru/pdf/10_Sep/S_2/05_Koura.pdf|conference=4th International Conference on the Chemistry and Physics of the Transactinide Elements|access-date=18 November 2018}}</ref> On the other hand, the same analysis suggests that proton shell closures may be relatively weak or even nonexistent in some cases such as <sup>354</sup>126, meaning that such nuclei might not be doubly magic and stability will instead be primarily determined by strong neutron shell closures.<ref name=magickoura/> Additionally, due to the enormously greater forces of [[coulomb repulsion|electromagnetic repulsion]] that must be overcome by the strong force at the second island (''Z'' = 164),<ref name=greinernuclei>{{cite journal|last=Greiner|first=W.|date=2013|title=Nuclei: superheavy-superneutronic-strange-and of antimatter|url=http://inspirehep.net/record/1221632/files/jpconf13_413_012002.pdf|journal=Journal of Physics: Conference Series|volume=413|issue=1|pages=012002|doi=10.1088/1742-6596/413/1/012002|bibcode=2013JPhCS.413a2002G|doi-access=free}}</ref> it is possible that nuclei around this region only exist as [[resonance (particle physics)|resonances]] and cannot stay together for a meaningful amount of time. It is also possible that some of the superactinides between these series may not actually exist because they are too far from both islands,<ref name=greinernuclei/> in which case the periodic table might end around ''Z'' = 130.<ref name="BFricke"/> The area of elements 121–156 where periodicity is in abeyance is quite similar to the gap between the two islands.<ref name=primefan/> Beyond element 164, the [[fissility]] line defining the limit of stability with respect to spontaneous fission may converge with the [[neutron drip line]], posing a limit to the existence of heavier elements.<ref name=SHlimit/> Nevertheless, further magic numbers have been predicted at ''Z'' = 210, 274, and 354 and ''N'' = 308, 406, 524, 644, and 772,<ref name=Denisov>{{cite journal|last=Denisov|first=V.|date=2005|title=Magic numbers of ultraheavy nuclei|journal=Physics of Atomic Nuclei|url= https://www.researchgate.net/publication/225734594|volume=68|issue=7|pages=1133–1137|doi=10.1134/1.1992567|bibcode=2005PAN....68.1133D|s2cid=119430168}}</ref> with two beta-stable doubly magic nuclei found at <sup>616</sup>210 and <sup>798</sup>274; the same calculation method reproduced the predictions for <sup>298</sup>Fl and <sup>472</sup>164. (The doubly magic nuclei predicted for ''Z'' = 354 are beta-unstable, with <sup>998</sup>354 being neutron-deficient and <sup>1126</sup>354 being neutron-rich.) Although additional stability toward alpha decay and fission are predicted for <sup>616</sup>210 and <sup>798</sup>274, with half-lives up to hundreds of microseconds for <sup>616</sup>210,<ref name=Denisov/> there will not exist islands of stability as significant as those predicted at ''Z'' = 114 and 164. As the existence of superheavy elements is very strongly dependent on stabilizing effects from closed shells, nuclear instability and fission will likely determine the end of the periodic table beyond these islands of stability.<ref name="BFricke"/><ref name=limit146/><ref name=SHlimit/> The International Union of Pure and Applied Chemistry (IUPAC) defines an element to exist if its lifetime is longer than 10<sup>−14</sup> seconds, which is the time it takes for the nucleus to form an electron cloud. However, a [[nuclide]] is generally considered to exist if its lifetime is longer than about 10<sup>−22</sup> seconds, which is the time it takes for [[nuclear structure]] to form. Consequently, it is possible that some ''Z'' values can only be realised in nuclides and that the corresponding elements do not exist.<ref name=colloq/> It is also possible that no further islands actually exist beyond 126, as the nuclear shell structure gets smeared out (as the electron shell structure already is expected to be around oganesson) and low-energy decay modes become readily available.<ref name=relqed>{{cite journal |last1=Schwerdtfeger |first1=Peter |last2=Pašteka |first2=Lukáš F. |last3=Punnett |first3=Andrew |last4=Bowman |first4=Patrick O. |date=2015 |title=Relativistic and quantum electrodynamic effects in superheavy elements |journal=Nuclear Physics A |volume=944 |issue=December 2015 |pages=551–577 |doi=10.1016/j.nuclphysa.2015.02.005|bibcode=2015NuPhA.944..551S }}</ref> In some regions of the table of nuclides, there are expected to be additional regions of stability due to non-spherical nuclei that have different magic numbers than spherical nuclei do; the egg-shaped <sup>270</sup>[[Hassium|Hs]] {{nowrap|1=(''Z'' = 108, ''N'' = 162)}} is one such deformed doubly magic nucleus.<ref>{{cite journal|last1=Dvorak|first1=J.|last2=Brüchle|first2=W.|last3=Chelnokov|first3=M.|last4=Dressler|first4=R.|last5=Düllmann|first5=Ch. E.|last6=Eberhardt|first6=K.|last7=Gorshkov|first7=V.|last8=Jäger|first8=E.|last9=Krücken|first9=R.|last10=Kuznetsov|first10=A.|last11=Nagame|first11=Y.|last12=Nebel|first12=F.|last13=Novackova|first13=Z.|last14=Qin|first14=Z.|last15=Schädel|first15=M.|last16=Schausten|first16=B.|last17=Schimpf|first17=E.|last18=Semchenkov|first18=A.|last19=Thörle|first19=P.|last20=Türler|first20=A.|last21=Wegrzecki|first21=M.|last22=Wierczinski|first22=B.|last23=Yakushev|first23=A.|last24=Yeremin|first24=A.|title=Doubly Magic Nucleus <sub>108</sub><sup>270</sup>Hs<sub>162</sub> |journal=Physical Review Letters|volume=97|issue=24|pages=242501|year=2006|doi=10.1103/PhysRevLett.97.242501|pmid=17280272|bibcode=2006PhRvL..97x2501D|url=https://www.dora.lib4ri.ch/psi/islandora/object/psi%3A16351}}</ref> In the superheavy region, the strong Coulomb repulsion of protons may cause some nuclei, including isotopes of oganesson, to assume a bubble shape in the ground state with a reduced central density of protons, unlike the roughly uniform distribution inside most smaller nuclei.<ref>{{cite journal |last1=LaForge |first1=Evan |last2=Price |first2=Will |last3=Rafelski |first3=Johann |title=Superheavy elements and ultradense matter |journal=The European Physical Journal Plus |date=15 September 2023 |volume=138 |issue=9 |page=812 |doi=10.1140/epjp/s13360-023-04454-8|arxiv=2306.11989 |bibcode=2023EPJP..138..812L }}</ref><ref>{{cite news |title=Physicists are pushing the periodic table to its limits {{!}} Science News |url=https://www.sciencenews.org/article/physics-periodic-table-future-superheavy-elements |access-date=25 December 2023 |date=27 February 2019}}</ref> Such a shape would have a very low fission barrier, however.<ref>{{cite journal |last1=Dechargé |first1=J. |last2=Berger |first2=J.-F. |last3=Girod |first3=M. |last4=Dietrich |first4=K. |title=Bubbles and semi-bubbles as a new kind of superheavy nuclei |journal=Nuclear Physics A |date=March 2003 |volume=716 |pages=55–86 |doi=10.1016/S0375-9474(02)01398-2|bibcode=2003NuPhA.716...55D }}</ref> Even heavier nuclei in some regions, such as <sup>342</sup>136 and <sup>466</sup>156, may instead become [[torus|toroidal]] or [[red blood cell]]-like in shape, with their own magic numbers and islands of stability, but they would also fragment easily.<ref>{{cite journal |last1=Agbemava |first1=S. E. |last2=Afanasjev |first2=A. V. |title=Hyperheavy spherical and toroidal nuclei: The role of shell structure |journal=Physical Review C |date=25 March 2021 |volume=103 |issue=3 |pages=034323 |doi=10.1103/PhysRevC.103.034323 |arxiv=2012.13799|bibcode=2021PhRvC.103c4323A }}</ref><ref>{{cite journal |last1=Afanasjev |first1=A.V. |last2=Agbemava |first2=S.E. |last3=Gyawali |first3=A. |title=Hyperheavy nuclei: Existence and stability |journal=Physics Letters B |date=July 2018 |volume=782 |pages=533–540 |doi=10.1016/j.physletb.2018.05.070|doi-access=free |arxiv=1804.06395 |bibcode=2018PhLB..782..533A }}</ref> ====Predicted decay properties of undiscovered elements==== As the main island of stability is thought to lie around <sup>291</sup>Cn and <sup>293</sup>Cn, undiscovered elements beyond [[oganesson]] may be very unstable and undergo [[alpha decay]] or [[spontaneous fission]] in microseconds or less. The exact region in which half-lives exceed one microsecond is unknown, though various models suggest that isotopes of elements heavier than [[unbinilium]] that may be produced in fusion reactions with available targets and projectiles will have half-lives under one microsecond and therefore may not be detected.<ref name=Karpov/> It is consistently predicted that there will exist regions of stability at ''N'' = 184 and ''N'' = 228, and possibly also at ''Z'' ~ 124 and ''N'' ~ 198. These nuclei may have half-lives of a few seconds and undergo predominantly alpha decay and spontaneous fission, though minor [[positron emission|beta-plus decay]] (or [[electron capture]]) branches may also exist.<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|issn=1062-8738|url=http://nrv.jinr.ru/karpov/publications/Palenzuela12_BRAS.pdf|doi=10.3103/S1062873812110172|bibcode=2012BRASP..76.1165P|s2cid=120690838}}</ref> Outside these regions of enhanced stability, [[fission barrier]]s are expected to drop significantly due to loss of stabilization effects, resulting in fission half-lives below [[attosecond|10<sup>−18</sup>]] seconds, especially in [[even and odd atomic nuclei|even–even nuclei]] for which hindrance is even lower due to [[nucleon pair breaking in fission|nucleon pairing]].<ref name=SHlimit/> In general, alpha decay half-lives are expected to increase with neutron number, from nanoseconds in the most neutron-deficient isotopes to seconds closer to the [[beta-stability line]].<ref name="sciencedirect1"/> For nuclei with only a few neutrons more than a magic number, [[nuclear binding energy|binding energy]] substantially drops, resulting in a break in the trend and shorter half-lives.<ref name="sciencedirect1"/> The most neutron deficient isotopes of these elements may also be unbound and undergo [[proton emission]]. [[Cluster decay]] (heavy particle emission) has also been proposed as an alternative decay mode for some isotopes,<ref>{{cite journal |last1=Poenaru |first1=Dorin N. |last2=Gherghescu |first2=R. A. |last3=Greiner |first3=W. |date=2012 |title=Cluster decay of superheavy nuclei |url=https://www.researchgate.net/publication/235507943 |journal=Physical Review C |volume=85 |issue=3 |pages=034615 |doi=10.1103/PhysRevC.85.034615 |access-date=2 May 2017|bibcode=2012PhRvC..85c4615P }}</ref> posing yet another hurdle to identification of these elements. ===Electron configurations=== The following are expected electron configurations of elements 119–174 and 184. The symbol [Og] indicates the probable electron configuration of oganesson (Z = 118), which is currently the last known element. The configurations of the elements in this table are written starting with [Og] because oganesson is expected to be the last prior element with a closed-shell (inert gas) configuration, 1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>6</sup> 3s<sup>2</sup> 3p<sup>6</sup> 3d<sup>10</sup> 4s<sup>2</sup> 4p<sup>6</sup> 4d<sup>10</sup> 4f<sup>14</sup> 5s<sup>2</sup> 5p<sup>6</sup> 5d<sup>10</sup> 5f<sup>14</sup> 6s<sup>2</sup> 6p<sup>6</sup> 6d<sup>10</sup> 7s<sup>2</sup> 7p<sup>6</sup>. Similarly, the [172] in the configurations for elements 173, 174, and 184 denotes the likely closed-shell configuration of element 172. Beyond element 123, no complete calculations are available and hence the data in this table must be taken as [[wiktionary:tentative|tentative]].<ref name="BFricke"/><ref name="BFricke1977"/><ref name="E123-vdSchoor2011">{{cite thesis|last=van der Schoor|first=K.|title=Electronic structure of element 123|url=http://fse.studenttheses.ub.rug.nl/14531/1/report.pdf|date=2016|publisher=Rijksuniversiteit Groningen}}</ref> In the case of element 123, and perhaps also heavier elements, several possible electron configurations are predicted to have very similar energy levels, such that it is very difficult to predict the [[ground state]]. All configurations that have been proposed (since it was understood that the Madelung rule probably stops working here) are included.<ref name="Umemoto"/><ref name="E123-vdSchoor2011"/><ref>{{Cite journal|url=https://link.springer.com/article/10.1007/s00214-010-0887-3|doi = 10.1007/s00214-010-0887-3|title = Are MCDF calculations 101% correct in the super-heavy elements range?|year = 2011|last1 = Indelicato|first1 = Paul|last2 = Bieroń|first2 = Jacek|last3 = Jönsson|first3 = Per|journal = Theoretical Chemistry Accounts|volume = 129|issue = 3–5|pages = 495–505|hdl = 2043/12984|s2cid = 54680128|hdl-access = free}}</ref> The predicted block assignments up to 172 are Kulsha's,<ref name=dications>{{Cite web|url=http://www.primefan.ru/stuff/chem/ptable/dications.html|title = Feasible electron configurations of dications up to Z = 172|access-date=2021-07-04}}</ref> following the expected available valence orbitals. There is, however, not a consensus in the literature as to how the blocks should work after element 138. :{| class="wikitable" ! colspan="3" | [[Chemical element]] !! [[Block (periodic table)|Block]] !! Predicted [[electron configuration]]s<ref name=Haire/><ref name="BFricke"/><ref name=nefedov/><ref name="BFricke1977"/> |-bgcolor="{{element color|s-block}}" || 119 || '''Uue''' || [[Ununennium]] ||s-block ||[Og] 8s<sup>1</sup> |-bgcolor="{{element color|s-block}}" || 120 || '''Ubn''' || [[Unbinilium]] ||s-block ||[Og] 8s<sup>2</sup> |-bgcolor="{{element color|g-block}}" || 121 || '''Ubu''' || [[Unbiunium]] ||g-block || [Og] 8s<sup>2</sup> 8p{{su|p=1|b=1/2}}<ref name=Umemoto/> |-bgcolor="{{element color|g-block}}" || 122 || '''Ubb''' || [[Unbibium]] ||g-block || [Og] 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=Umemoto/><br/>[Og] 7d<sup>1</sup> 8s<sup>2</sup> 8p{{su|p=1|b=1/2}} |-bgcolor="{{element color|g-block}}" || 123 || '''Ubt''' || Unbitrium ||g-block || [Og] 6f<sup>1</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig>{{cite web |url=http://www.primefan.ru/stuff/chem/ptable/ptable.html |title=Archived copy |website=primefan.ru |access-date=15 January 2022 |archive-url=https://web.archive.org/web/20160305034205/http://www.primefan.ru/stuff/chem/ptable/ptable.html |archive-date=5 March 2016 |url-status=dead}}</ref><br/>[Og] 6f<sup>1</sup> 7d<sup>1</sup> 8s<sup>2</sup> 8p{{su|p=1|b=1/2}}<ref name=Umemoto/><ref name="E123-vdSchoor2011"/><br/>[Og] 6f<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=1|b=1/2}}<br/>[Og] 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 8p{{su|p=1|b=3/2}}<ref name="E123-vdSchoor2011"/> |-bgcolor="{{element color|g-block}}" || 124 || '''Ubq''' || [[Unbiquadium]] ||g-block || [Og] 6f<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=Umemoto/><ref name=econfig/><br/>[Og] 6f<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=1|b=1/2}} |-bgcolor="{{element color|g-block}}" || 125 || '''Ubp''' || Unbipentium ||g-block || [Og] 6f<sup>4</sup> 8s<sup>2</sup> 8p{{su|p=1|b=1/2}}<ref name=Umemoto/><br/>[Og] 5g<sup>1</sup> 6f<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/><br/>[Og] 5g<sup>1</sup> 6f<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=1|b=1/2}}<br/>[Og] 8s<sup>2</sup> 0.81(5g<sup>1</sup> 6f<sup>2</sup> 8p{{su|p=2|b=1/2}}) + 0.17(5g<sup>1</sup> 6f<sup>1</sup> 7d<sup>2</sup> 8p{{su|p=1|b=1/2}}) + 0.02(6f<sup>3</sup> 7d<sup>1</sup> 8p{{su|p=1|b=1/2}}) |-bgcolor="{{element color|g-block}}" || 126 || '''Ubh''' || [[Unbihexium]] ||g-block || [Og] 5g<sup>1</sup> 6f<sup>4</sup> 8s<sup>2</sup> 8p{{su|p=1|b=1/2}}<ref name=Umemoto/><br/>[Og] 5g<sup>2</sup> 6f<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/><br/>[Og] 5g<sup>2</sup> 6f<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=1|b=1/2}}<br/>[Og] 8s<sup>2</sup> 0.998(5g<sup>2</sup> 6f<sup>3</sup> 8p{{su|p=1|b=1/2}}) + 0.002(5g<sup>2</sup> 6f<sup>2</sup> 8p{{su|p=2|b=1/2}}) |-bgcolor="{{element color|g-block}}" || 127 || '''Ubs''' || Unbiseptium ||g-block || [Og] 5g<sup>2</sup> 6f<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=Umemoto/><br/>[Og] 5g<sup>3</sup> 6f<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/><br/>[Og] 8s<sup>2</sup> 0.88(5g<sup>3</sup> 6f<sup>2</sup> 8p{{su|p=2|b=1/2}}) + 0.12(5g<sup>3</sup> 6f<sup>1</sup> 7d<sup>2</sup> 8p{{su|p=1|b=1/2}}) |-bgcolor="{{element color|g-block}}" || 128 || '''Ubo''' ||Unbioctium||g-block || [Og] 5g<sup>3</sup> 6f<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=Umemoto/><br/>[Og] 5g<sup>4</sup> 6f<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/><br/>[Og] 8s<sup>2</sup> 0.88(5g<sup>4</sup> 6f<sup>2</sup> 8p{{su|p=2|b=1/2}}) + 0.12(5g<sup>4</sup> 6f<sup>1</sup> 7d<sup>2</sup> 8p{{su|p=1|b=1/2}}) |-bgcolor="{{element color|g-block}}" || 129 || '''Ube''' || Unbiennium ||g-block || [Og] 5g<sup>4</sup> 6f<sup>3</sup> 7d<sup>1</sup> 8s<sup>2</sup> 8p{{su|p=1|b=1/2}}<br/>[Og] 5g<sup>4</sup> 6f<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=Umemoto/><ref name=econfig/><br/>[Og] 5g<sup>5</sup> 6f<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>4</sup> 6f<sup>3</sup> 7d<sup>1</sup> 8s<sup>2</sup> 8p{{su|p=1|b=1/2}} |-bgcolor="{{element color|g-block}}" || 130 || '''Utn''' || Untrinilium ||g-block || [Og] 5g<sup>5</sup> 6f<sup>3</sup> 7d<sup>1</sup> 8s<sup>2</sup> 8p{{su|p=1|b=1/2}}<br/>[Og] 5g<sup>5</sup> 6f<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=Umemoto/><ref name=econfig/><br/>[Og] 5g<sup>6</sup> 6f<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>5</sup> 6f<sup>3</sup> 7d<sup>1</sup> 8s<sup>2</sup> 8p{{su|p=1|b=1/2}} |-bgcolor="{{element color|g-block}}" || 131 || '''Utu''' || Untriunium ||g-block || [Og] 5g<sup>6</sup> 6f<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=Umemoto/><ref name=econfig/><br/>[Og] 5g<sup>7</sup> 6f<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 8s<sup>2</sup> 0.86(5g<sup>6</sup> 6f<sup>3</sup> 8p{{su|p=2|b=1/2}}) + 0.14(5g<sup>6</sup> 6f<sup>2</sup> 7d<sup>2</sup> 8p{{su|p=1|b=1/2}}) |-bgcolor="{{element color|g-block}}" || 132 || '''Utb''' || Untribium ||g-block || [Og] 5g<sup>7</sup> 6f<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/><br/>[Og] 5g<sup>8</sup> 6f<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} |-bgcolor="{{element color|g-block}}" || 133 || '''Utt''' || Untritrium ||g-block || [Og] 5g<sup>8</sup> 6f<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|g-block}}" || 134 || '''Utq''' || Untriquadium ||g-block || [Og] 5g<sup>8</sup> 6f<sup>4</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|g-block}}" || 135 || '''Utp''' || Untripentium ||g-block || [Og] 5g<sup>9</sup> 6f<sup>4</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|g-block}}" || 136 || '''Uth''' || Untrihexium ||g-block || [Og] 5g<sup>10</sup> 6f<sup>4</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|g-block}}" || 137 || '''Uts''' || Untriseptium ||g-block || [Og] 5g<sup>11</sup> 6f<sup>4</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|g-block}}" || 138 || '''Uto''' || Untrioctium ||g-block || [Og] 5g<sup>12</sup> 6f<sup>4</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/><br/>[Og] 5g<sup>12</sup> 6f<sup>3</sup> 7d<sup>1</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} |-bgcolor="{{element color|g-block}}" || 139 || '''Ute''' || Untriennium ||g-block || [Og] 5g<sup>13</sup> 6f<sup>3</sup> 7d<sup>1</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/><br/>[Og] 5g<sup>13</sup> 6f<sup>2</sup> 7d<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} |-bgcolor="{{element color|g-block}}" || 140 || '''Uqn''' || Unquadnilium ||g-block || [Og] 5g<sup>14</sup> 6f<sup>3</sup> 7d<sup>1</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/><br/>[Og] 5g<sup>15</sup> 6f<sup>1</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 8p{{su|p=2|b=3/2}} |-bgcolor="{{element color|g-block}}" || 141 || '''Uqu''' || Unquadunium ||g-block || [Og] 5g<sup>15</sup> 6f<sup>2</sup> 7d<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|g-block}}" || 142 || '''Uqb''' || Unquadbium ||g-block || [Og] 5g<sup>16</sup> 6f<sup>2</sup> 7d<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|f-block}}" || 143 || '''Uqt''' || Unquadtrium ||f-block || [Og] 5g<sup>17</sup> 6f<sup>2</sup> 7d<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|f-block}}" || 144 || '''Uqq''' || Unquadquadium ||f-block || [Og] 5g<sup>18</sup> 6f<sup>2</sup> 7d<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/><br/>[Og] 5g<sup>18</sup> 6f<sup>1</sup> 7d<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>17</sup> 6f<sup>2</sup> 7d<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 8s<sup>2</sup> 0.95(5g<sup>17</sup> 6f<sup>2</sup> 7d<sup>3</sup> 8p{{su|p=2|b=1/2}}) + 0.05(5g<sup>17</sup> 6f<sup>4</sup> 7d<sup>1</sup> 8p{{su|p=2|b=1/2}}) |-bgcolor="{{element color|f-block}}" || 145 || '''Uqp''' || Unquadpentium ||f-block || [Og] 5g<sup>18</sup> 6f<sup>3</sup> 7d<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|f-block}}" || 146 || '''Uqh''' || Unquadhexium ||f-block || [Og] 5g<sup>18</sup> 6f<sup>4</sup> 7d<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|f-block}}" || 147 || '''Uqs''' || Unquadseptium ||f-block || [Og] 5g<sup>18</sup> 6f<sup>5</sup> 7d<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|f-block}}" || 148 || '''Uqo''' || Unquadoctium ||f-block || [Og] 5g<sup>18</sup> 6f<sup>6</sup> 7d<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|f-block}}" || 149 || '''Uqe''' || Unquadennium ||f-block || [Og] 5g<sup>18</sup> 6f<sup>6</sup> 7d<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|f-block}}" || 150 || '''Upn''' || Unpentnilium ||f-block || [Og] 5g<sup>18</sup> 6f<sup>6</sup> 7d<sup>4</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>7</sup> 7d<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|f-block}}" || 151 || '''Upu''' || Unpentunium ||f-block || [Og] 5g<sup>18</sup> 6f<sup>8</sup> 7d<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|f-block}}" || 152 || '''Upb''' || Unpentbium ||f-block || [Og] 5g<sup>18</sup> 6f<sup>9</sup> 7d<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|f-block}}" || 153 || '''Upt''' || Unpenttrium ||f-block || [Og] 5g<sup>18</sup> 6f<sup>10</sup> 7d<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>11</sup> 7d<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|f-block}}" || 154 || '''Upq''' || Unpentquadium ||f-block || [Og] 5g<sup>18</sup> 6f<sup>11</sup> 7d<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>12</sup> 7d<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|f-block}}" || 155 || '''Upp''' || Unpentpentium ||f-block || [Og] 5g<sup>18</sup> 6f<sup>12</sup> 7d<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>13</sup> 7d<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|f-block}}" || 156 || '''Uph''' || Unpenthexium ||f-block|| [Og] 5g<sup>18</sup> 6f<sup>13</sup> 7d<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>2</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|d-block}}" || 157 || '''Ups''' || Unpentseptium ||d-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>3</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|d-block}}" || 158 || '''Upo''' || Unpentoctium ||d-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>4</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|d-block}}" || 159 || '''Upe''' || Unpentennium ||d-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>5</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>4</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 9s<sup>1</sup><ref name=econfig/> |-bgcolor="{{element color|d-block}}" {{Anchor|Uhn|Unhexnilium}} || 160 || '''Uhn''' || Unhexnilium ||d-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>6</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>5</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 9s<sup>1</sup><ref name=econfig/> |-bgcolor="{{element color|d-block}}" || 161 || '''Uhu''' || Unhexunium ||d-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>7</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>6</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 9s<sup>1</sup><ref name=econfig/> |-bgcolor="{{element color|d-block}}" || 162 || '''Uhb''' || Unhexbium ||d-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>8</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>7</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 9s<sup>1</sup><ref name=econfig/> |-bgcolor="{{element color|d-block}}" || 163 || '''Uht''' || Unhextrium ||d-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>9</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>8</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 9s<sup>1</sup><ref name=econfig/> |-bgcolor="{{element color|d-block}}" || 164 || '''Uhq''' || Unhexquadium ||d-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|d-block}}" || 165 || '''Uhp''' || Unhexpentium ||d-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 9s<sup>1</sup><ref name=econfig/> |-bgcolor="{{element color|d-block}}" || 166 || '''Uhh''' || Unhexhexium ||d-block ||[Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 9s<sup>2</sup><ref name=econfig/> |-bgcolor="{{element color|p-block}}" || 167 || '''Uhs''' || Unhexseptium ||p-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 9s<sup>2</sup> 9p{{su|p=1|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 8p{{su|p=1|b=3/2}} 9s<sup>2</sup><ref name=econfig/> |-bgcolor="{{element color|p-block}}" || 168 || '''Uho''' || Unhexoctium ||p-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 9s<sup>2</sup> 9p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 8p{{su|p=2|b=3/2}} 9s<sup>2</sup><ref name=econfig/> |-bgcolor="{{element color|p-block}}" || 169 || '''Uhe''' || Unhexennium ||p-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 8p{{su|p=1|b=3/2}} 9s<sup>2</sup> 9p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 8p{{su|p=3|b=3/2}} 9s<sup>2</sup><ref name=econfig/> |-bgcolor="{{element color|p-block}}" || 170 || '''Usn''' || Unseptnilium ||p-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 8p{{su|p=2|b=3/2}} 9s<sup>2</sup> 9p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 8p{{su|p=4|b=3/2}} 9s<sup>2</sup><ref name=econfig/> |-bgcolor="{{element color|p-block}}" || 171 || '''Usu''' || Unseptunium ||p-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 8p{{su|p=3|b=3/2}} 9s<sup>2</sup> 9p{{su|p=2|b=1/2}}<br/>[Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 8p{{su|p=4|b=3/2}} 9s<sup>2</sup> 9p{{su|p=1|b=1/2}}<ref name=econfig/> |-bgcolor="{{element color|p-block}}" || 172 || '''{{Not a typo|Usb}}''' || Unseptbium ||p-block || [Og] 5g<sup>18</sup> 6f<sup>14</sup> 7d<sup>10</sup> 8s<sup>2</sup> 8p{{su|p=2|b=1/2}} 8p{{su|p=4|b=3/2}} 9s<sup>2</sup> 9p{{su|p=2|b=1/2}}<ref name=econfig/> |- || 173 || '''Ust''' || Unsepttrium || ? || [172] 6g<sup>1</sup><br/>[172] 9p{{su|p=1|b=3/2}}<br/>[172] 10s<sup>1</sup><ref name=eliav2023>{{cite web |url=https://indico.jinr.ru/event/3622/contributions/20027/attachments/15317/25832/Ephraim%20Eliav%20Yerevan-2023F.pptx |title=Benchmark atomic electronic structures calculations at the edge of Periodic Table |last=Eliav |first=Ephraim |date=26 April 2023 |website=jinr.ru |publisher=JINR |access-date=29 July 2023 |quote=}}</ref> |- || 174 || '''Usq''' || Unseptquadium || ? || [172] 8d<sup>1</sup> 10s<sup>1</sup><ref name=eliav2023/> |- || ... || ... || ... || ... || ... |- || 184 || '''Uoq''' || Unoctquadium || ? || [172] 6g<sup>5</sup> 7f<sup>4</sup> 8d<sup>3</sup> |}
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