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A period 8 element is any one of 46 hypothetical chemical elements (ununennium through unhexquadium]]) belonging to an eighth period of the periodic table of the elements. They may be referred to using IUPAC systematic element names. None of these elements have been synthesized, and it is possible that none have isotopes with stable enough nuclei to receive significant attention in the near future. It is also probable that, due to drip instabilities, only the lower period 8 elements are physically possible and the periodic table may end soon after the island of stability at unbihexium with atomic number 126. The names given to these unattested elements are all IUPAC systematic names.

If it were possible to produce sufficient quantities of sufficiently long-lived isotopes of these elements that would allow the study of their chemistry, these elements may well behave very differently from those of previous periods. This is because their electronic configurations may be altered by quantum and relativistic effects, as the energy levels of the 5g, 6f, 7d and 8p orbitals are so close to each other that they may well exchange electrons with each other. 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.

History

There are currently seven periods in the periodic table of chemical elements, culminating with atomic number 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 seventh period, as they are calculated to contain elements with filled g-orbitals in their ground state. An eight-period table containing these elements was suggested by Glenn T. Seaborg in 1969. No elements in this region have been synthesized or discovered in nature. While Seaborg's version of the extended period had the heavier elements following the pattern set by lighter elements, as it did not take into account relativistic effects, models that take relativistic effects into account do not. Pekka Pyykkö and B. Fricke used computer modeling to calculate the positions of elements up to Z = 172 (comprising periods 8 and 9), and found that several were displaced from the Madelung rule.

Attempts at synthesis

The first two period 8 elements are elements 119 and 120. The necessary condition for synthesising them is to have a sensitivity on the order of femtobarns, which is currently out of reach of even the most advanced facilities.

The synthesis of ununennium was attempted in 1985 by bombarding a target of einsteinium-254 with calcium-48 ions at the superHILAC accelerator at Berkeley, California. No atoms were identified, leading to a limiting yield of 300 nb.

${\displaystyle \,_{99}^{254}\mathrm {Es} +\,_{20}^{48}\mathrm {Ca} \to \,_{119}^{302}\mathrm {Uue} ^{*}\to \mathrm {no\ atoms} }$

It is highly unlikely that this reaction will be useful given the extremely difficult task of making sufficient amounts of Es-254 to make a large enough target to increase the sensitivity of the experiment to the required level, due to the rarity of the element, and extreme rarity of the isotope.

In March–April 2007, the synthesis of unbinilium was attempted at the Flerov Laboratory of Nuclear Reactions in Dubna by bombarding a plutonium-244 target with iron-58 ions. Initial analysis revealed that no atoms of element 120 were produced providing a limit of 400 fb for the cross section at the energy studied.

${\displaystyle \,_{94}^{244}\mathrm {Pu} +\,_{26}^{58}\mathrm {Fe} \to \,_{120}^{302}\mathrm {Ubn} ^{*}\to \mathrm {fission\ only} }$

The Russian team are planning to upgrade their facilities before attempting the reaction again.

In April 2007, the team at GSI attempted to create unbinilium using uranium-238 and nickel-64:

${\displaystyle \,_{92}^{238}\mathrm {U} +\,_{28}^{64}\mathrm {Ni} \to \,_{120}^{302}\mathrm {Ubn} ^{*}\to \mathrm {fission\ only} }$

No atoms were detected providing a limit of 1.6 pb on the cross section at the energy provided. The GSI repeated the experiment with higher sensitivity in three separate runs from April–May 2007, Jan–March 2008, and Sept–Oct 2008, all with negative results and providing a cross section limit of 90 fb.

The superactinides would only be detectable if they lie near the hypothesised island of stability. The stability of these elements depends on the location of the island of stability; if the island is centred around a low Z, most superactinides would be too unstable to be detected, but if it is centred around a higher Z, there is a possibility of detecting the lower superactinides. The only superactinides that have had attempts to synthesise them are elements 122, 124, 126 and 127.

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

${\displaystyle \,_{92}^{238}\mathrm {U} +\,_{30}^{66}\mathrm {Zn} \to \,_{122}^{304}\mathrm {Ubb} ^{*}\to \mathrm {no\ atoms} .}$

No atoms were detected and a yield limit of 5 mb (5,000,000 pb) 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:

${\displaystyle \,_{92}^{238}\mathrm {U} +\,_{30}^{70}\mathrm {Zn} \to \,_{122}^{308}\mathrm {Ubb} ^{*}\to \mathrm {no\ atoms} .}$

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 fb.

Another unsuccessful attempt to synthesize unbibium was carried out in 1978 at the GSI, where a natural erbium target was bombarded with xenon-136 ions:

${\displaystyle \,_{68}^{nat}\mathrm {Er} +\,_{54}^{136}\mathrm {Xe} \to \,^{298,300,302,303,304,306}\mathrm {Ubb} ^{*}\to \ {\mbox{no atoms}}.}$

The two attempts in the 1970s to synthesize unbibium were caused by research investigating whether superheavy elements could potentially be naturally occurring.

Several experiments have been performed between 2000–2004 at the Flerov laboratory of Nuclear Reactions studying the fission characteristics of the compound nucleus Ubb. Two nuclear reactions have been used, namely Cm+Fe and Pu+Ni. The results have revealed how nuclei such as this fission predominantly by expelling closed shell nuclei such as Sn (Z=50, N=82). It was also found that the yield for the fusion-fission pathway was similar between Ca and Fe projectiles, indicating a possible future use of Fe projectiles in superheavy element formation.

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 and 10, relative to thorium. 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 and Nature Physics but both turned it down without sending it for peer review.

A criticism of the technique, previously used in purportedly identifying lighter thorium isotopes by mass spectrometry, was published in Physical Review C in 2008. A rebuttal by the Marinov group was published in Physical Review C after the published comment.

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. 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 = 114, 120, and 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:

${\displaystyle \,_{92}^{238}\mathrm {U} +\,_{32}^{nat}\mathrm {Ge} \to \,^{308,310,311,312,314}\mathrm {Ubq} ^{*}\to \mathrm {fission} .}$

The team reported that they had been able to identify compound nuclei of unbiquadium fissioning with half-lives > 10 s. Although very short, the ability to measure such decays indicated a strong shell effect at Z=124. A similar phenomenon was found for Z=120 but not for Z=114.

The first attempt to synthesize unbihexium was performed in 1971 by Bimbot et al. using the hot fusion reaction:

${\displaystyle \,_{90}^{232}\mathrm {Th} +\,_{36}^{84}\mathrm {Kr} \to \,_{126}^{316}\mathrm {Ubh} ^{*}\to \mathrm {no\ atoms} }$

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.

${\displaystyle \,_{73}^{nat}\mathrm {Ta} +\,_{54}^{136}\mathrm {Xe} \to \,^{316,317}\mathrm {Ubs} ^{*}\to {\mbox{no atoms}}.}$

All other elements in this region of the periodic table and beyond have not received any attempts to synthesise them.

See also

• Extension of the periodic table beyond the seventh period
• Nucleon drip line

Notes

1. The heaviest element that has been synthesized to date is ununoctium with atomic number 118, which is the last period 7 element.
2. Element 122 was claimed to exist naturally in April 2008, but this claim was widely believed to be erroneous.

References

1. ^ Cite error: The named reference EB was invoked but never defined (see the help page).
2. ^ Emsley, John (2011). Nature's Building Blocks: An A-Z Guide to the Elements (New ed.). New York, NY: Oxford University Press. ISBN 978-0-19-960563-7.
3. Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1063/1.1672054, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1063/1.1672054 instead.
4. Seaborg, Glenn (August 26, 1996). "An Early History of LBNL".
5. Frazier, K. (1978). "Superheavy Elements". Science News. 113 (15): 236–238. doi:10.2307/3963006. JSTOR 3963006.
6. ^ Royal Society of Chemistry, "Heaviest element claim criticised", Chemical World.
7. "Extended elements: new periodic table". 2010.
8. Fricke, B.; Greiner, W.; Waber, J. T. (1971). "The continuation of the periodic table up to Z = 172. The chemistry of superheavy elements". Theoretica chimica acta. 21 (3). Springer-Verlag: 235–260. doi:10.1007/BF01172015. Retrieved 28 November 2012.
9. R. W. Lougheed, J. H. Landrum, E. K. Hulet, J. F. Wild, R. J. Dougan, A. D. Dougan, H. Gäggeler, M. Schädel, K. J. Moody, K. E. Gregorich, and G. T. Seaborg (1985). "Search for superheavy elements using Ca + Es reaction". Physical Reviews C. 32 (5): 1760–1763. Bibcode:1985PhRvC..32.1760L. doi:10.1103/PhysRevC.32.1760.{{cite journal}}: CS1 maint: multiple names: authors list (link)
10. THEME03-5-1004-94/2009
11. Oganessian; Samanta, C.; Basu, D.; et al. (2009). "Attempt to produce element 120 in the Pu+Fe reaction". Phys. Rev. C. 73: 024603. arXiv:nucl-th/0507054. Bibcode:2006PhRvC..73a4612C. doi:10.1103/PhysRevC.73.014612. {{cite journal}}: Explicit use of et al. in: |author= (help)
12. see Flerov lab annual reports 2000–2004 inclusive http://www1.jinr.ru/Reports/Reports_eng_arh.html
13. ^ Marinov, A. (2008). "Evidence for a long-lived superheavy nucleus with atomic mass number A=292 and atomic number Z=~122 in natural Th". International Journal of Modern Physics E. 19: 131. arXiv:0804.3869. Bibcode:2010IJMPE..19..131M. doi:10.1142/S0218301310014662. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
14. ^ A. Marinov; I. Rodushkin; Y. Kashiv; L. Halicz; I. Segal; A. Pape; R. V. Gentry; H. W. Miller; D. Kolb; R. Brandt (2007). "Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes". Phys. Rev. C. 76 (2): 021303(R). arXiv:nucl-ex/0605008. Bibcode:2007PhRvC..76b1303M. doi:10.1103/PhysRevC.76.021303.{{cite journal}}: CS1 maint: multiple names: authors list (link)
15. ^ Marinov, A.; Rodushkin, I.; Kashiv, Y.; Halicz, L.; Segal, I.; Pape, A.; Gentry, R.; Miller, H.; Kolb, D. (2007). "Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes". Physical Review C. 76 (2): 021303. arXiv:nucl-ex/0605008. Bibcode:2007PhRvC..76b1303M. doi:10.1103/PhysRevC.76.021303.
16. R. C. Barber; J. R. De Laeter (2009). "Comment on "Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes"". Phys. Rev. C. 79 (4): 049801. Bibcode:2009PhRvC..79d9801B. doi:10.1103/PhysRevC.79.049801.{{cite journal}}: CS1 maint: multiple names: authors list (link)
17. A. Marinov; I. Rodushkin; Y. Kashiv; L. Halicz; I. Segal; A. Pape; R. V. Gentry; H. W. Miller; D. Kolb; R. Brandt (2009). "Reply to "Comment on 'Existence of long-lived isomeric states in naturally-occurring neutron-deficient Th isotopes'"". Phys. Rev. C. 79 (4): 049802. Bibcode:2009PhRvC..79d9802M. doi:10.1103/PhysRevC.79.049802.{{cite journal}}: CS1 maint: multiple names: authors list (link)
18. J. Lachner; I. Dillmann; T. Faestermann; G. Korschinek; M. Poutivtsev; G. Rugel (2008). "Search for long-lived isomeric states in neutron-deficient thorium isotopes". Phys. Rev. C. 78 (6): 064313. arXiv:0907.0126. Bibcode:2008PhRvC..78f4313L. doi:10.1103/PhysRevC.78.064313.{{cite journal}}: CS1 maint: multiple names: authors list (link)
19. Marinov, A.; Rodushkin, I.; Pape, A.; Kashiv, Y.; Kolb, D.; Brandt, R.; Gentry, R. V.; Miller, H. W.; Halicz, L. (2009). "Existence of Long-Lived Isotopes of a Superheavy Element in Natural Au" (PDF). International Journal of Modern Physics E. 18 (3). World Scientific Publishing Company: 621–629. arXiv:nucl-ex/0702051. Bibcode:2009IJMPE..18..621M. doi:10.1142/S021830130901280X. Retrieved February 12, 2012.
20. http://hal.archives-ouvertes.fr/docs/00/12/91/31/PDF/WAPHE06_EPJ_preprint1.pdf

v t e Extended periodic table
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ① H He ② Li Be B C N O F Ne ③ Na Mg Al Si P S Cl Ar ④ K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr ⑤ Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe ⑥ Cs Ba La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn ⑦ Fr Ra Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og ⑧ 119 120 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 ‍ ‍ 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142
s-block g-block f-block d-block p-block

• Periodic table