Editing Extended periodic table (section)

===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&nbsp;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&nbsp;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&nbsp;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&nbsp;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}}</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&nbsp;[[electronvolt|eV]]; element 122: 5.6&nbsp;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&nbsp;[[Atomic orbital|orbital]] on element 126 and the 2[[p-orbital|p]]&nbsp;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&nbsp;pm per element; in the [[actinide]]s, it is about 3&nbsp;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&nbsp;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&nbsp;kJ/mol and its metallic radius approximately 170&nbsp;picometers. With a relative atomic mass of around 445&nbsp;u,<ref name=Fricke/> it should be a very heavy metal with a density of around 26&nbsp;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&nbsp;[[electronvolt|eV]]. It should be at most moderately reactive, having a first ionization energy that should be around 685&nbsp;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&nbsp;[[picometer|pm]], very close to that of the much lighter [[magnesium]], despite its expected atomic weight of around 474&nbsp;[[atomic mass unit|u]] which is about 19.5&nbsp;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&nbsp;g·cm<sup>−3</sup>, over twice that of [[osmium]], currently the most dense element known, at 22.61&nbsp;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&nbsp;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&nbsp;[[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&nbsp;kJ/mol; element 172, 1090&nbsp;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&nbsp;eV,<ref name=eliav2023/> compared to the experimentally known 3.894&nbsp;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&nbsp;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>