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#REDIRECT ] |
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A '''period 8 element''' is any one of 46 hypothetical ]s (] through unhexquadium) belonging to an eighth ] of the ]. They may be referred to using ] ]s. None of these elements have been ],<ref group="note">The heaviest element that has been synthesized to date is ] with atomic number 118, which is the last ].</ref> 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 ], only the lower period 8 elements are physically possible and the periodic table may end soon after the ] at ] with atomic number 126.<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}}</ref>{{Rp|593|date=November 2012}} The names given to these unattested elements are all ]. |
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{{R with possibilities}} |
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{{R printworthy}} |
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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 ]s may be altered by ] and ] effects, as the energy levels of the 5g, 6f, 7d and 8p<sub>1/2</sub> ] 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 ] series that would have extremely similar chemical properties that would be quite unrelated to elements of lower atomic number.<ref name="Fricke"/> |
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==History== |
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There are currently seven ]s in the ] of ], culminating with ] 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-]s in their ground state. An eight-period table containing these elements was suggested by ] 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. 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 ], models that take relativistic effects into account do not. ] and B. Fricke used computer modeling to calculate the positions of elements up to '']'' = 172 (comprising periods 8 and ]), 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><ref name="Fricke">{{cite journal |last1=Fricke |first1=B. |last2=Greiner |first2=W. |last3=Waber |first3=J. T. |year=1971 |title=The continuation of the periodic table up to Z = 172. The chemistry of superheavy elements |journal=Theoretica chimica acta |volume=21 |issue=3 |pages=235–260 |publisher=Springer-Verlag |doi=10.1007/BF01172015 |url=http://link.springer.com/article/10.1007%2FBF01172015?LI=true# |accessdate=28 November 2012}}</ref> Fricke predicted the structure of the extended periodic table up to ''Z'' = 172 to be: |
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{{Compact extended periodic table}} |
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==Predicted properties== |
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===8s elements=== |
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<div style="float: right; margin: 1px; font-size:85%;"> |
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:{| class="wikitable sortable" |
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|+ Some predicted properties of elements 119 and 120<ref name="Fricke"/><ref name="Haire"/> |
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! Property |
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! 119 |
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! 120 |
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! ] |
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! ] |
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| ] |
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| ] |
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! Valence ] |
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| 8s<sup>1</sup> |
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| 8s<sup>2</sup> |
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! Stable ]s |
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| '''1''', 3 |
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| '''2''', 4 |
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! First ] |
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| 437.1 ] |
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| 578.9 kJ/mol |
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! ] |
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| 260 pm |
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| 200 pm |
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! ] |
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| 3 g/cm<sup>3</sup> |
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| 7 g/cm<sup>3</sup> |
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! ] |
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| 0–30 ] |
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| 680 °C |
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</div> |
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The first two elements of period 8 are expected to be ] and ], elements 119 and 120. Their electron configurations should have the 8s shell being filled. However, the 8s orbital is relativistically stabilized and contracted and thus, elements 119 and 120 should be more like ] and ] than their immediate neighbours above, ] and ]. Another effect of the relativistic contraction of the 8s orbital is that the ] of these two elements should be about the same of those of francium and radium. They should behave like normal ] and ]s, normally forming +1 and +2 ]s respectively, but the relativistic destabilization of the 7p<sub>3/2</sub> subshell and the relatively low ] 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| last = Haire|first = Richard G.| chapter = Transactinides and the future elements| publisher = ]| year = 2006| isbn = 1-4020-3555-1| location = Dordrecht, The Netherlands| edition = 3rd| ref = CITEREFHaire2006}}</ref> |
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===Superactinides=== |
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The superactinide series is expected to contain elements ] to 155. In the superactinide series, the 7d<sub>3/2</sub>, 8p<sub>1/2</sub>, 6f<sub>5/2</sub> and 5g<sub>7/2</sub> shells should all fill simultaneously. The first superactinide, unbiunium (element 121), should be a ] of ] and ] and should have similar properties to them. 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, ] (element 126) would usually form a +8 oxidation state, and even higher oxidation states for the next few elements may be possible. 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 ] orbitals to form and influence the chemistry of the superactinides in new ways, although the absence of ''g'' electrons in known elements makes predicting their chemistry more difficult.<ref name=Fricke/> |
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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</sub> 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</sub> 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 ]s outside the chemically inactive 8s and 8p<sub>1/2</sub> shells. This would cause element 154 to be very ], so that it may exhibit properties similar to those of the noble gases.<ref name=Fricke/><ref name=Haire/> |
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Similarly to the ], there should be a superactinide contraction in the superactinide series where the ] of the superactinides are smaller than expected. In the ]s, the contraction is about 4.4 pm per element; in the ]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/> |
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===Transition metals=== |
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{{empty section|date=December 2012}} |
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==Synthesis== |
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{{empty section|date=November 2012}} |
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<!--here we can write about E119 and E120 being close by, and the non-feasibility of the rest – Zagrebaev on User talk:Double sharp--> |
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==See also== |
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* ] |
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* ] |
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==Notes== |
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{{reflist|group=note}} |
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==References== |
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{{reflist}} |
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{{Compact extended periodic table}} |
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{{DEFAULTSORT:Period 8 Element}} |
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