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71.174.208.245: Hyperlinked some key terms

{{disputed|date=November 2012}}
{{periodic table (superactinides location)}}
A '''superactinide''' is any one of 32 hypothetical [[chemical element]]s from [[atomic number]]s 121 ([[unbiunium]]) through 153 ([[unpenttrium]]), at which the 5g and 6f [[electron shell]]s are filled up. They may be referred to using [[IUPAC]] [[systematic element name]]s. None of these elements have been [[synthetic element|synthesized]],<ref group="note">The heaviest element that has been synthesized to date is [[ununoctium]] with atomic number 118, which is the last [[period 7 element]].</ref> and it is possible that none have isotopes with stable enough nuclei to receive significant attention in the near future. Synthesis has only been attempted for elements [[unbibium|122]], [[unbiquadium|124]], [[unbihexium|126]], and [[unbiseptium|127]]. It is also probable that, due to [[Proton drip line|drip instabilities]], only the lighter superactinides are physically possible and the periodic table may end soon after the [[island of stability]] expected to be centered at element 126.<ref name=EB/> The theoretical existence of the series was proposed by [[Glenn T. Seaborg]], winner of the 1951 [[Nobel Prize in Chemistry]].

If it were possible to produce sufficient quantities of these elements that would allow the study of their chemistry, these elements might well behave very differently from those of previous periods. This is because their [[electronic configuration]]s may be altered by [[quantum mechanics|quantum]] and [[Theory of relativity|relativistic]] effects, as the energy levels of the 5g, 6f and 7d [[atomic orbital|orbitals]] are so close to each other that they may well exchange electrons with each other.<ref>{{cite doi|10.1063/1.1672054}}</ref> This would result in a large number of elements in the superactinide series that would have extremely similar chemical properties that would be quite unrelated to elements of lower [[atomic number]]s.<ref name=EB/>

==History==
There are currently seven [[period (periodic table)|period]]s in the [[periodic table]] of [[chemical elements]], culminating with [[atomic number]] [[ununoctium|118]]. If further elements with higher atomic numbers than this are discovered, they will be placed in additional periods, laid out (as with the existing periods) to illustrate periodically recurring trends in the properties of the elements concerned. Any additional periods are expected to contain a larger number of elements than the [[Period 7 element|seventh period]], as they are calculated to have an additional so-called [[g-block]], containing 18 elements with partially filled g-[[atomic orbital|orbital]]s in each period. An [[Period 8 element|eight-period]] table containing this block was suggested by [[Glenn T. Seaborg]] in 1969.<ref name="LBNL">{{ cite web |url=http://www.lbl.gov/LBL-PID/Nobelists/Seaborg/65th-anniv/29.html |title= An Early History of LBNL|first=Glenn |last=Seaborg |date=August 26, 1996}}</ref><ref>{{cite journal | doi = 10.2307/3963006 | last1 = Frazier | first1 = K. | title = Superheavy Elements | journal = Science News | volume = 113 | issue = 15 | pages = 236–238 | year = 1978 | jstor = 3963006}}</ref> No elements in this region have been synthesized or discovered in nature.{{#tag:ref|[[Unbibium|Element 122]] was claimed to exist naturally in April 2008 by [[Amnon Marinov]], but this claim was widely believed to be erroneous.<ref name="RSC-Ubb">[[Royal Society of Chemistry]], "[http://rsc.org/chemistryworld/News/2008/May/02050802.asp Heaviest element claim criticised]", Chemical World.</ref>|name=natural-122|group=note}} While Seaborg's version of the extended period had the heavier elements following the pattern set by lighter elements, other models do not. [[Pekka Pyykkö]], for example, used computer modeling to calculate the positions of elements up to ''[[Atomic number|Z]]'' = [[unseptbium|172]], and found that several were displaced from the Madelung rule.<ref name="rsc.org">{{Cite web|url=http://www.rsc.org/Publishing/ChemScience/Volume/2010/11/Extended_elements.asp |title=Extended elements: new periodic table |year=2010}}</ref>

== Expected properties ==
The first element of the g-block may have [[atomic number]] 121, and thus would have the [[Systematic element name|systematic name]] [[unbiunium]]. Elements in this region are likely to be highly unstable with respect to [[radioactive decay]], and have extremely short [[half life|half lives]], although [[unbihexium|element 126]] is hypothesized to be within an [[island of stability]] that is resistant to fission but not to [[alpha decay]]. It is not clear how many elements beyond the expected island of stability are physically possible, or even if the superactindes are complete.

According to the orbital approximation in [[quantum mechanics|quantum mechanical]] descriptions of atomic structure, the g-block would correspond to elements with partially filled g-orbitals. However, [[spin-orbit coupling]] effects reduce the validity of the orbital approximation substantially for elements of high [[atomic number]]s.

== Elements ==
If [[superheavy element]]s continue to follow the [[Aufbau principle]], the superactinide series contains the following elements:

{{wide template|periodic table (superactinides)}}

If the [[Extended periodic table#Pyykkö model|Pyykkö model]] is correct, the superactinide series contains the following elements instead:<ref name="pyykko">{{Cite journal|last1=Pyykkö|first1=Pekka|title=A suggested periodic table up to Z≤ 172, based on Dirac–Fock calculations on atoms and ions|journal=Physical Chemistry Chemical Physics|volume=13|issue=1|pages=161–8|year=2011|pmid=20967377|doi=10.1039/c0cp01575j|bibcode = 2011PCCP...13..161P }}</ref>

{{wide template|periodic table (superactinides, by Pyykkö)}}
{{periodic table legend|
|child=no|caption=Legend
|theme1=block|predicted1=yes}}

All of these hypothetical undiscovered elements are named by the [[International Union of Pure and Applied Chemistry]] (IUPAC) [[systematic element name]] standard which creates a generic name for use until the element has been discovered, confirmed, and an official name approved.

=== g-block superactinides ===

==== Attempts at synthesis ====
[[File:GSI-Darmstadt-Südbau.jpg|thumb|right|250px|The GSI Helmholtz Centre for Heavy Ion Research, a heavy ion research center in [[Darmstadt, Germany]]]]
The only elements in this region of the [[periodic table]] that have had attempts to synthesise them are elements [[Unbibium|122]], [[Unbiquadium|124]], [[Unbihexium|126]], and [[Unbiseptium|127]].

The first attempt to synthesize [[unbibium]] was performed in 1972 by Flerov ''et al.'' at [[JINR]], using the hot fusion reaction:

: <math>\,^{238}_{92}\mathrm{U} + \,^{66}_{30}\mathrm{Zn} \to \,^{304}_{122}\mathrm{Ubb} ^{*} \to \ \mbox{no atoms}.</math>

No atoms were detected and a yield limit of 5 [[Barn (unit)|mb]] (5,000,000 [[barn (unit)|pb]]){{Dubious|reason=5mb=5,000,000,000 pb, so one of the values must be wrong |date=August 2010}} was measured. Current results (see [[flerovium]]) have shown that the sensitivity of this experiment was too low by at least 6 orders of magnitude.

In 2000, the [[Gesellschaft für Schwerionenforschung]] performed a very similar experiment with much higher sensitivity:

: <math>\,^{238}_{92}\mathrm{U} + \,^{70}_{30}\mathrm{Zn} \to \,^{308}_{122}\mathrm{Ubb} ^{*} \to \ \mbox{no atoms}.</math>

These results indicate that the synthesis of such heavier elements remains a significant challenge and further improvements of beam intensity and experimental efficiency is required. The sensitivity should be increased to 1 [[barn (unit)|fb]].

Several experiments have been performed between 2000 and 2004 at the Flerov laboratory of Nuclear Reactions studying the fission characteristics of the compound nucleus 306Ubb. Two nuclear reactions have been used, namely 248Cm+58Fe and 242Pu+64Ni. The results have revealed how nuclei such as this fission predominantly by expelling [[nuclear shell model|closed shell]] nuclei such as 132Sn (Z=50, N=82). It was also found that the yield for the fusion-fission pathway was similar between 48Ca and 58Fe projectiles, indicating a possible future use of 58Fe projectiles in superheavy element formation.<ref>see Flerov lab annual reports 2000–2004 inclusive http://www1.jinr.ru/Reports/Reports_eng_arh.html</ref>

On April 24, 2008, a group led by Amnon Marinov at the [[Hebrew University of Jerusalem]] claimed to have found single atoms of unbibium in naturally occurring [[thorium]] deposits at an abundance of between 10−11 and 10−12, relative to thorium.<ref>{{cite journal |last=Marinov |first=A. |coauthors=Rodushkin, I.; Kolb, D.; Pape, A.; Kashiv, Y.; Brandt, R.; Gentry, R. V.; Miller, H. W. |title=Evidence for a long-lived superheavy nucleus with atomic mass number A=292 and atomic number Z=~122 in natural Th |journal= International Journal of Modern Physics E|year=2008 |arxiv=0804.3869 |bibcode = 2010IJMPE..19..131M |doi = 10.1142/S0218301310014662 |volume=19 |pages=131 }}</ref> The claim of Marinov ''et al.'' was criticized by a part of the scientific community, and Marinov says he has submitted the article to the journals ''[[Nature (journal)|Nature]]'' and ''[[Nature Physics]]'' but both turned it down without sending it for peer review.<ref name="RSC-Ubb"/>

A criticism of the technique, previously used in purportedly identifying lighter [[thorium]] isotopes by mass spectrometry,<ref>{{cite journal |journal=Phys. Rev. C |title=Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes |year=2007 |volume=76 |page=021303(R)|doi=10.1103/PhysRevC.76.021303 |author=A. Marinov; I. Rodushkin; Y. Kashiv; L. Halicz; I. Segal; A. Pape; R. V. Gentry; H. W. Miller; D. Kolb; R. Brandt |arxiv = nucl-ex/0605008 |bibcode = 2007PhRvC..76b1303M |issue=2}}</ref><ref>{{cite journal |arxiv=nucl-ex/0605008 |doi=10.1103/PhysRevC.76.021303 |title=Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes |year=2007 |journal=Physical Review C |volume=76 |pages=021303 |last1=Marinov|first1=A.|last2=Rodushkin |first2=I. |last3=Kashiv |first3=Y.|last4=Halicz |first4=L. |last5=Segal |first5=I. |last6=Pape |first6=A. |last7=Gentry |first7=R. |last8=Miller|first8=H. |last9=Kolb |first9=D. |first10=R.|last10=Brandt |displayauthors=10|bibcode = 2007PhRvC..76b1303M |issue=2 }}</ref>
was published in Physical Review C in 2008.<ref>{{cite journal |journal=Phys. Rev. C |title=Comment on "Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes" |year=2009 |volume=79|pages=049801 |doi=10.1103/PhysRevC.79.049801 |author=R. C. Barber; J. R. De Laeter |bibcode = 2009PhRvC..79d9801B|issue=4 }}</ref> A rebuttal by the Marinov group was published in Physical Review C after the published comment.<ref>{{cite journal |journal=Phys. Rev. C |title=Reply to "Comment on 'Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes'" |year=2009 |volume=79 |pages=049802|doi=10.1103/PhysRevC.79.049802 |author=A. Marinov; I. Rodushkin; Y. Kashiv; L. Halicz; I. Segal; A. Pape; R. V. Gentry; H. W. Miller; D. Kolb; R. Brandt |bibcode = 2009PhRvC..79d9802M |issue=4 }}</ref>

A repeat of the [[thorium]]-experiment using the superior method of Accelerator Mass Spectrometry (AMS) failed to confirm the results, despite a 100-fold better sensitivity.<ref>{{cite journal |journal=Phys. Rev. C |title=Search for long-lived isomeric states in neutron-deficient thorium isotopes |year=2008 |volume=78 |page= 064313|doi=10.1103/PhysRevC.78.064313 |author=J. Lachner; I. Dillmann; T. Faestermann; G. Korschinek; M. Poutivtsev; G. Rugel |bibcode = 2008PhRvC..78f4313L |issue=6 |arxiv = 0907.0126 }}</ref> This result throws considerable doubt on the results of the Marinov collaboration with regards to their claims of long-lived isotopes of [[thorium]], [[roentgenium]] and [[unbibium]].

In a series of experiments, scientists at GANIL have attempted to measure the direct and delayed fission of compound nuclei of elements with Z=[[Flerovium|114]], [[Unbinilium|120]], and [[Unbiquadium|124]] in order to probe shell effects in this region and to pinpoint the next spherical [[proton]] shell. In 2006, with full results published in 2008, the team provided results from a reaction involving the bombardment of a natural [[germanium]] target with [[uranium]] ions:

: <math>\,^{238}_{92}\mathrm{U} + \,^{nat}_{32}\mathrm{Ge} \to \,^{308,310,311,312,314}\mathrm{Ubq} ^{*} \to \ fission.</math>

The team reported that they had been able to identify compound nuclei fissioning with half-lives > 10−18 s. Although very short, the ability to measure such decays indicated a strong shell effect at [[unbiquadium|Z=124]]. A similar phenomenon was found for [[unbinilium|Z=120]] but not for [[flerovium|Z=114]].<ref>{{cite journal| journal=European Physical Journal D |title=Direct experimental evidence for very long fission times of super-heavy elements |year=2007 |author=M. Morjean; J. L. Charvet; A. Chbini; M. Chevallier; C. Cohen; D. Dauvergne; R. Dayras; A. Drouart; J. D. Frankland; D. Jacquet; R. Kirsch; M. Laget; P. Lautesse; A. L'hoir; A. Marchix; L. Naplas; M. Parlog; C. Ray; C. Schmitt; C. Stodel; L. Tassan-Got; C. Volant |url=http://hal.archives-ouvertes.fr/docs/00/12/91/31/PDF/WAPHE06_EPJ_preprint1.pdf}}</ref>

[[File:Island of Stability.svg|thumb|400px|right|alt=A 3D graph of stability of elements vs. number of protons Z and neutrons N, showing a "mountain chain" running diagonally through the graph from the low to high numbers, as well as an "island of stability" at high N and Z.|3-dimensional rendering of the theoretical island of stability around N=178 and Z=118]]
The first attempt to synthesize [[unbihexium]] was performed in 1971 by Bimbot ''et al.'' using the hot fusion reaction:

: <math>\,^{232}_{90}\mathrm{Th} + \,^{84}_{36}\mathrm{Kr} \to \,^{316}_{126}\mathrm{Ubh} ^{*} \to \ no \ atoms</math>

A high energy [[alpha particle]] was observed and taken as possible evidence for the synthesis of [[unbihexium]]. Recent research suggests that this is highly unlikely as the sensitivity of experiments performed in 1971 would have been several orders of magnitude too low according to current understanding. To date, no other attempt has been made to synthesize unbihexium.

[[Unbiseptium]] has had one failed attempt at synthesis in 1978 at the Darmstadt UNILAC accelerator by bombarding a natural [[tantalum]] target with [[xenon]] ions. No atoms were detected.<ref name="emsley">{{cite book|last=Emsley|first=John|title=Nature's Building Blocks: An A-Z Guide to the Elements|edition=New|year=2011|publisher=Oxford University Press|location=New York, NY|isbn=978-0-19-960563-7|page=593}}</ref>

:<math>\,^{nat}_{73}\mathrm{Ta} + \,^{136}_{54}\mathrm{Xe} \to \,^{316, 317}\mathrm{Ubs} ^{*} \to \mbox{no atoms}.</math>

==== Element 137 ====
[[Untriseptium]], element 137, is sometimes called '''[[feynmanium]]''' (symbol Fy) because [[Richard Feynman]] noted<ref>
{{cite web
|author=G. Elert
|date=
|title=Atomic Models
|url=http://physics.info/atomic-models/
|work=The Physics Hypertextbook
|accessdate=2009-10-09
}}</ref> that a simplistic interpretation of the [[Theory of relativity|relativistic]] [[Dirac equation]] runs into problems with electron orbitals at ''Z'' > 1/α = 137, suggesting that neutral atoms cannot exist beyond untriseptium, and that a [[periodic table of elements]] based on [[Atomic orbital|electron orbitals]] therefore breaks down at this point. However, a more rigorous analysis calculates the limit to be ''Z'' ≈ 173, indicating that [[unsepttrium]] (element 173) is in fact the last possible neutral atom.

===== Bohr model breakdown {{Anchor|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}{137.036}</math>

where ''Z'' is the [[atomic number]], and ''α'' is the [[fine structure constant]], a measure of the strength of electromagnetic interactions.<ref>See for example {{cite book
|author=R. Eisberg, R. Resnick
|year=1985
|title=Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles
|publisher=[[John Wiley & Sons|Wiley]]
|isbn=
}}</ref> Under this approximation, any element with an [[atomic number]] greater than 137 would require 1s [[electrons]] to be traveling faster than ''c'', the [[speed of light]]. Hence the non-relativistic Bohr model is clearly inaccurate when applied to such an element.

===== The Dirac equation =====
The [[Theory of relativity|relativistic]] [[Dirac equation]] also has problems for ''Z'' > 137, for the ground state energy is

: <math>E=m c^2 \sqrt{1-Z^2 \alpha^2}</math>

where ''m'' is the rest mass of the electron. 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
|author=J.D. Bjorken, S.D. Drell
|year=1964
|title=Relativistic Quantum Mechanics
|publisher=[[McGraw-Hill]]
|isbn=
}}</ref>

More accurate calculations including the effects of the finite size of the nucleus indicate that the binding energy first exceeds 2''mc''2 for ''Z'' > ''Z''cr ≈ 173. For''Z'' > ''Z''cr, if the innermost orbital is not filled, the electric field of the nucleus will pull an electron out of the vacuum, resulting in the spontaneous emission of a positron.<ref>
{{cite journal
|author=W. Greiner, S. Schramm
|year=2008
|title=[[American Journal of Physics]]
|volume=76 |pages=509
|doi=
}}, and references therein.</ref>

=== f-block and d-block superactinides ===
The [[Relativistic quantum chemistry|relativistic]] and [[quantum effects]] for the electron clouds of the f-block elements are expected to be even greater than those for the g-block elements, because these elements have higher atomic number. If these elements could actually be observed, they would likely be observed to have similar chemical properties, but the effect of the closeness of the 5g and 6f (and possibly also the 7d and 8p) subshells is unclear and difficult to predict because of the relativistic and quantum effects. These orbitals, being so close in energy, may fill together all at the same time, resulting in a series of very similar elements with many barely distinguishable [[oxidation state]]s. The basis of [[periodic trends]] based on [[electron configuration]]s may thus no longer hold.<ref name=EB>{{cite web|author=Seaborg|url=http://www.britannica.com/EBchecked/topic/603220/transuranium-element|title=transuranium element (chemical element)|publisher=Encyclopædia Britannica|date=c. 2006|accessdate=2010-03-16}}</ref>

The existence of such atoms is probably theoretically possible as the upper limit for atomic number is likely ''Z'' = 173 due to the [[speed of light|light-speed limit]],<ref name=Greiner>{{cite journal |author=Walter Greiner and Stefan Schramm |title=Resource Letter QEDV-1: The QED vacuum |journal=American Journal of Physics |volume=76 |page=509 |year=2008 |doi=10.1119/1.2820395 |bibcode = 2008AmJPh..76..509G |issue=6 }}, and references therein.</ref> after which assigning electron shells would be nonsensical and elements would only be able to exist as ions, but it is not clear if our technology will ever be enough to synthesise them.

Although [[Unpenttrium|element 153]] would likely be taken to be the last superactinide based on previous periods, the electron configurations for the [[d-block]] and [[p-block]] [[period 8 element]]s would likely be nothing more than mathematical extrapolation because of the extreme [[quantum effects|quantum]] and [[Relativistic quantum chemistry|relativistic effects]] the electron clouds will experience. In the unlikely case that their chemical properties may eventually be studied, it is likely that all existing classifications will be inadequate to describe them. Due to the breakdown of periodic trends expected in this region due to the closeness of energy of the 5g, 6f, 7d and 8p orbitals and other [[relativistic quantum chemistry|relativistic effects]], it seems likely that the properties and placement in the periodic table of these elements may be of only formal significance.<ref name=EB />

== Related substances ==

=== Lanthanides and actinides ===
{{Empty section|date=November 2012}}

=== Eka-superactinides ===
{{periodic table (eka-superactinides location)}}
Related to the superactinides are the [[Mendeleev's predicted elements|eka]]-superactinides, one row further down in the periodic table, which are elements 171 through 203.<ref name=Greiner/>

== See also ==
*[[Lanthanide]]
*[[Actinide]]
*[[Period 8 element]]

== Notes ==
{{Reflist|group=note}}

== Bibliography ==
*J. Huheey: ''Anorganische Chemie'', 2. Auflage, 1995

== References ==
{{Reflist|30em}}

{{PeriodicTablesFooter}}
{{Compact extended periodic table}}

[[Category:Nuclear physics]]
[[Category:Chemical element groups]]
[[Category:Periodic table]]

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