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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 ]. Sometimes, elements 169 to 172 are also considered to be in period 8 as their outermost electrons fill the 8p<sub>3/2</sub> subshells, despite behaving chemically more like the ]s. 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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{{Redirect category shell| |
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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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{{R from merge}} |
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{{R with possibilities}} |
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{{R from subtopic}} |
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{{R printworthy}} |
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}} |
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] |
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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="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><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> Fricke predicted the structure of the extended periodic table up to ''Z'' = 172 to be: |
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{{Extended periodic table (by Fricke, 32 columns, compact)}} |
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==Predicted properties== |
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===Chemical and physical 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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! ] |
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| 630 ] |
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| 1700 °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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The transition metals in period 8 are expected to be element 156 to 164. 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 such that these elements will still behave chemically like their lighter ] in the periodic table, showing the same oxidation states as they do, in contrast to earlier predictions which predicted the period 8 transition metals to have main oxidation states two less than those of their lighter congeners.<ref name=Fricke/><ref name=Haire/> |
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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. Calculations predict that the 7d electrons of element 164 (unhexquadium) should participate very readily in chemical reactions, so that unhexquadium should be able to show +6 and +4 oxidation states in addition to the normal +2 state in ]s with strong ]s. Unhexquadium should thus be able to form compounds like Uhq(])<sub>4</sub>, Uhq(])<sub>4</sub> (both ]), and {{chem|Uhq(])|2|2-}} (]), which is very different behavior from that of ], which unhexquadium would be a heavier ] of if not for relativistic effects. Unhexquadium should be a ] metal like ], and metallic unhexquadium should have a high melting point as it is predicted to bond ]. It should also have some similarities to ] as well as to the other group 12 elements. The eighth period of the periodic table is expected to end here.<ref name=Fricke/><ref name=Haire/> |
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<div style="float: center; margin: 1px; font-size:85%;"> |
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:{| class="wikitable sortable" |
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|+ Some predicted properties of the 7d transition metals. The metallic radii and densities are first approximations.<ref name="Fricke"/><ref name="Haire"/> |
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! Property |
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! 156 |
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! 157 |
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! 158 |
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! 159 |
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! 160 |
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! 161 |
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! 162 |
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! 163 |
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! 164 |
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! ] |
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! ] |
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| ] |
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| ] |
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| ] |
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| ] |
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| ] |
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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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| 7d<sup>2</sup> |
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| 7d<sup>3</sup> |
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| 7d<sup>4</sup> |
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| 7d<sup>5</sup> |
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| 7d<sup>6</sup> |
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| 7d<sup>7</sup> |
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| 7d<sup>8</sup> |
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| 7d<sup>9</sup> |
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| 7d<sup>10</sup> |
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|- |
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! Stable ]s |
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| 2, 4 |
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| 3, 5 |
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| 4, 6 |
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| 1, 5, 7 |
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| 2, 6, 8 |
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| 3, 7 |
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| 4, 8 |
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| 3, 5 |
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| 0, 2, 4, 6 |
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! First ] |
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| 395.6 kJ/mol |
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| 453.5 kJ/mol |
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| 521.0 kJ/mol |
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| 337.7 kJ/mol |
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| 424.5 kJ/mol |
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| 472.8 kJ/mol |
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| 559.6 kJ/mol |
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| 617.5 kJ/mol |
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| 685.0 kJ/mol |
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! ] |
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| 170 pm |
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| 163 pm |
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| 157 pm |
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| 152 pm |
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| 148 pm |
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| 148 pm |
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| 149 pm |
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| 152 pm |
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| 158 pm |
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! ] |
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| 26 g/cm<sup>3</sup> |
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| 28 g/cm<sup>3</sup> |
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| 30 g/cm<sup>3</sup> |
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| 33 g/cm<sup>3</sup> |
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| 36 g/cm<sup>3</sup> |
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| 40 g/cm<sup>3</sup> |
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| 45 g/cm<sup>3</sup> |
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| 47 g/cm<sup>3</sup> |
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| 46 g/cm<sup>3</sup> |
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</div> |
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===Nuclear properties=== |
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The first ] is expected to be centered around ]-306 (with 122 protons and 184 neutrons),<ref name=Kratz> |
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{{cite conference |
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|last1=Kratz |first1=J. V. |
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|date=5 September 2011 |
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|title=The Impact of Superheavy Elements on the Chemical and Physical Sciences |
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|url=http://tan11.jinr.ru/pdf/06_Sep/S_1/02_Kratz.pdf |
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|conference=4th International Conference on the Chemistry and Physics of the Transactinide Elements |
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|accessdate=27 August 2013 |
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}}</ref> and the second is expected to be center around ]-482 (with 164 protons and 318 neutrons).<ref>http://www.eurekalert.org/pub_releases/2008-04/acs-nse031108.php</ref><ref>http://link.springer.com/article/10.1007%2FBF01406719/lookinside/000.png</ref> |
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==Synthesis== |
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The only period 8 elements that have had synthesis attempts were elements 119, 120, 122, 124, 126, and 127. So far, none of these synthesis attempts were successful. |
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===Ununennium=== |
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The synthesis of ununennium was attempted in 1985 by bombarding a target of ]-254 with ]-48 ions at the superHILAC accelerator at Berkeley, California: |
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:<math>\,^{254}_{99}\mathrm{Es} + \,^{48}_{20}\mathrm{Ca} \to \,^{302}_{119}\mathrm{Uue} ^{*} </math> |
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No atoms were identified, leading to a limiting yield of 300 ].<ref>{{cite journal|title=Search for superheavy elements using <sup>48</sup>Ca + <sup>254</sup>Es<sup>g</sup> reaction|author=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 ]|journal=Physical Reviews C|year=1985|pages=1760–1763|url=http://link.aps.org/abstract/PRC/v32/p1760|doi=10.1103/PhysRevC.32.1760|volume=32|issue=5|bibcode = 1985PhRvC..32.1760L }}</ref> |
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As of May 2012, plans are under way to attempt to synthesize the isotopes <sup>295</sup>Uue and <sup>296</sup>Uue by bombarding a target of ] with ] at the ] in ], Germany:<ref name="economist">, ]</ref><ref>http://fias.uni-frankfurt.de/kollo/Duellmann_FIAS-Kolloquium.pdf</ref> |
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:<math>\,^{249}_{97}\mathrm{Bk} + \,^{50}_{22}\mathrm{Ti} \to \,^{296}_{119}\mathrm{Uue} \,+3\,^{1}_{0}\mathrm{n}</math> |
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:<math>\,^{249}_{97}\mathrm{Bk} + \,^{50}_{22}\mathrm{Ti} \to \,^{295}_{119}\mathrm{Uue} \,+4\,^{1}_{0}\mathrm{n}</math> |
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====Target-projectile combinations leading to Z=119 compound nuclei==== |
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The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with an atomic number of 119. |
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{|class="wikitable" style="text-align:center" |
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!Target!!Projectile!!CN!!Attempt result |
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!<sup>254</sup>Es |
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|<sup>48</sup>Ca||<sup>302</sup>Uue||{{no|Failure to date}} |
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!<sup>249</sup>Bk |
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|<sup>50</sup>Ti||<sup>299</sup>Uue||{{unk|Planned reaction}} |
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===Unbinilium=== |
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Attempts to date to synthesize the element using fusion reactions at low excitation energy have met with failure, although there are reports that the fission of nuclei of unbinilium at very high excitation has been successfully measured, indicating a strong shell effect at Z=120. |
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In March–April 2007, the synthesis of unbinilium was attempted at the ] in ] by bombarding a ]-244 target with ]-58 ]s.<ref></ref> Initial analysis revealed that no atoms of element 120 were produced providing a limit of 400 ] for the cross section at the energy studied.<ref>{{cite journal|journal=Phys. Rev. C|volume=79|page=024603|year=2009|title=Attempt to produce element 120 in the <sup>244</sup>Pu+<sup>58</sup>Fe reaction|doi=10.1103/PhysRevC.79.024603|last1=Oganessian|first1=Yu. Ts.|last2=Utyonkov|first2=V.|last3=Lobanov|first3=Yu.|last4=Abdullin|first4=F.|last5=Polyakov|first5=A.|last6=Sagaidak|first6=R.|last7=Shirokovsky|first7=I.|last8=Tsyganov|first8=Yu.|last9=Voinov|first9=A.|last10=N.N.|displayauthors=9|issue=2 |bibcode = 2009PhRvC..79b4603O }}</ref> |
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:<math>\,^{244}_{94}\mathrm{Pu} + \,^{58}_{26}\mathrm{Fe} \to \,^{302}_{120}\mathrm{Ubn} ^{*} \to \ \mathit{fission\ only}</math> |
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The Russian team are planning to upgrade their facilities before attempting the reaction again.<ref name=Duellmann>>http://fias.uni-frankfurt.de/kollo/Duellmann_FIAS-Kolloquium.pdf</ref> |
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In April 2007, the team at ] attempted to create unbinilium using ]-238 and ]-64:<ref name=Duellmann/> |
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:<math>\,^{238}_{92}\mathrm{U} + \,^{64}_{28}\mathrm{Ni} \to \,^{302}_{120}\mathrm{Ubn} ^{*} \to \ \mathit{fission\ only}</math> |
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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.<ref name=Duellmann/> |
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In June–July 2010, scientists at the GSI attempted the fusion reaction:<ref name=Duellmann/> |
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:<math>\,^{248}_{96}\mathrm{Cm} + \,^{54}_{24}\mathrm{Cr} \to \,^{302}_{120}\mathrm{Ubn} ^{*} </math> |
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They were unable to detect any atoms but exact details are not currently available.<ref name=Duellmann/> |
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In August–October 2011, a different team at the GSI using the TASCA facility tried the new reaction:<ref name=Duellmann/> |
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:<math>\,^{249}_{98}\mathrm{Cf} + \,^{50}_{22}\mathrm{Ti} \to \,^{299}_{120}\mathrm{Ubn} ^{*} </math> |
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Results from this experiment are not yet available.<ref name=Duellmann/> |
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In 2008, the team at GANIL, France, described the results from a new technique which attempts to measure the fission ] of a compound nucleus at high excitation energy, since the yields are significantly higher than from neutron evaporation channels. It is also a useful method for probing the effects of shell closures on the survivability of compound nuclei in the super-heavy region, which can indicate the exact position of the next proton shell (Z=114, 120, 124, or 126). |
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The team studied the nuclear fusion reaction between uranium ions and a target of natural nickel: |
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::::<math>\,^{238}_{92}\mathrm{U} + \,^{nat}_{28}\mathrm{Ni} \to \,^{296,298,299,300,302}\mathrm{Ubn} ^{*} \to \ \mathit{fission}.</math> |
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The results indicated that nuclei of unbinilium were produced at high (~70 MeV) excitation energy which underwent fission with measurable half-lives > 10<sup>−18</sup> s. Although very short, the ability to measure such a process indicates a strong shell effect at Z=120. At lower excitation energy (see neutron evaporation), the effect of the shell will be enhanced and ground-state nuclei can be expected to have relatively long half-lives. This result could partially explain the relatively long half-life of <sup>294</sup>] measured in experiments at Dubna. Similar experiments have indicated a similar phenomenon at Z=124 (see ]) but not for ], suggesting that the next proton shell does in fact lie at Z>120.<ref>{{cite journal|doi=10.1103/Physics.1.12|title=How stable are the heaviest nuclei?|year=2008|author=Natowitz, Joseph|journal=Physics|volume=1|pages=12|bibcode = 2008PhyOJ...1...12N }}</ref><ref>{{cite journal|journal=Phys. Rev. Lett.|volume=101|year=2008|page=072701|title=Fission Time Measurements: A New Probe into Superheavy Element Stability|author=Morjean, M. et al.|doi=10.1103/PhysRevLett.101.072701|pmid=18764526|bibcode=2008PhRvL.101g2701M|issue=7}}</ref> |
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The team at RIKEN have begun a program utilizing <sup>248</sup>Cm targets and have indicated future experiments to probe the possibility of Z=120 being the next magic number using the aforementioned nuclear reactions to form <sup>302</sup>Ubn.<ref>see slide 11 in </ref> |
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====Target-projectile combinations leading to Z=120 compound nuclei==== |
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The below table contains various combinations of targets and projectiles which could be used to form compound nuclei with an atomic number of 120. |
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{|class="wikitable" style="text-align:center" |
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! Target !! Projectile !! CN !! Attempt result |
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!<sup>208</sup>Pb |
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|<sup>88</sup>Sr||<sup>296</sup>Ubn||{{unk|Reaction yet to be attempted<ref name=Haire/>}} |
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!<sup>238</sup>U |
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|<sup>64</sup>Ni||<sup>302</sup>Ubn||{{no|Failure to date, σ < 94 fb}} |
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!<sup>244</sup>Pu |
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|<sup>58</sup>Fe||<sup>302</sup>Ubn||{{no|Failure to date, σ < 0.4 pb}} |
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!<sup>248</sup>Cm |
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|<sup>54</sup>Cr||<sup>302</sup>Ubn||{{no|Failure to date, not all details available}} |
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!<sup>250</sup>Cm |
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|<sup>54</sup>Cr||<sup>304</sup>Ubn||{{unk|Reaction yet to be attempted}} |
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!<sup>249</sup>Cf |
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|<sup>50</sup>Ti||<sup>299</sup>Ubn||{{unk|Results are not yet available}} |
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!<sup>252</sup>Cf |
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|<sup>50</sup>Ti||<sup>302</sup>Ubn||{{unk|Reaction yet to be attempted}} |
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!<sup>257</sup>Fm |
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|<sup>48</sup>Ca||<sup>305</sup>Ubn||{{unk|Reaction yet to be attempted}} |
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===Unbibium=== |
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The first attempt to synthesize unbibium was performed in 1972 by ] ''et al.'' at ], using the hot fusion reaction:<ref name="emsley"/> |
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:<math>\,^{238}_{92}\mathrm{U} + \,^{66}_{30}\mathrm{Zn} \to \,^{304}_{122}\mathrm{Ubb} ^{*} \to \ \mbox{no atoms}.</math> |
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No atoms were detected and a yield limit of 5 ] (5,000,000,000 ]) was measured. Current results (see ]) have shown that the sensitivity of this experiment was too low by at least 6 orders of magnitude.{{Citation needed|date=February 2012}} |
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In 2000, the ] (GSI) performed a very similar experiment with much higher sensitivity:<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=588}}</ref> |
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:<math>\,^{238}_{92}\mathrm{U} + \,^{70}_{30}\mathrm{Zn} \to \,^{308}_{122}\mathrm{Ubb} ^{*} \to \ \mbox{no atoms}.</math> |
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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 ].{{Citation needed|date=February 2012}} |
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Another unsuccessful attempt to synthesize unbibium was carried out in 1978 at the GSI, where a natural ] target was bombarded with ] ions:<ref name="emsley"/> |
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:<math>\,^{nat}_{68}\mathrm{Er} + \,^{136}_{54}\mathrm{Xe} \to \,^{298,300,302,303,304,306}\mathrm{Ubb} ^{*} \to \ \mbox{no atoms}.</math> |
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The two attempts in the 1970s to synthesize unbibium were caused by research investigating whether superheavy elements could potentially be naturally occurring.<ref name="emsley"/> |
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Several experiments have been performed between 2000-2004 at the Flerov laboratory of Nuclear Reactions studying the fission characteristics of the compound nucleus <sup>306</sup>Ubb. Two nuclear reactions have been used, namely <sup>248</sup>Cm + <sup>58</sup>Fe and <sup>242</sup>Pu + <sup>64</sup>Ni.<ref name="emsley"/> The results have revealed how nuclei such as this fission predominantly by expelling ] nuclei such as <sup>132</sup>Sn (Z=50, N=82). It was also found that the yield for the fusion-fission pathway was similar between <sup>48</sup>Ca and <sup>58</sup>Fe projectiles, indicating a possible future use of <sup>58</sup>Fe projectiles in superheavy element formation.<ref>see Flerov lab annual reports 2000–2004 inclusive http://www1.jinr.ru/Reports/Reports_eng_arh.html</ref> |
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===Unbiquadium=== |
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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 ] effects in this region and to pinpoint the next spherical proton shell. This is because having complete nuclear shells (or, equivalently, having a ] of ]s or ]s) would confer more stability on the nuclei of such superheavy elements, thus moving closer to the ]. 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: |
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:<math>\,^{238}_{92}\mathrm{U} + \,^{nat}_{32}\mathrm{Ge} \to \,^{308,310,311,312,314}\mathrm{Ubq} ^{*} \to \ fission.</math> |
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The team reported that they had been able to identify compound nuclei fissioning with half-lives > 10<sup>−18</sup> s. A compound nucleus is a loose combination of ]s that have not arranged themselves into nuclear shells yet. It has no internal structure and is held together only by the collision forces between the target and projectile nuclei. It is estimated that it requires around 10<sup>−14</sup> s for the nucleons to arrange themselves into nuclear shells, at which point the compound nucleus becomes an ], and this number is used by ] as the minimum ] a claimed isotope must have to potentially be recognised as being discovered. Thus, the GANIL experiments do not count as a discovery of element 124.<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=590}}</ref> |
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===Unbihexium=== |
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The first and only attempt to synthesize unbihexium, which was unsuccessful, was performed in 1971 at ] by ] and John M. Alexander<!--don't link; the article titled "John M. Alexander" goes to a different John M. Alexander--> using the hot fusion reaction:<ref name="emsley"/> |
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: {{nuclide2|thorium|232|link=y}} + {{nuclide2|krypton|84|link=y}} → {{nuclide2|unbihexium|316}}* → ''no atoms''<!-- please, drop the attitude to use the resource-consuming <math> for any (non-mathematical) crap which one cannot easily type-as-it-reads on an en-US keyboard. learn templates, HTML and Unicode --> |
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A high energy ] was observed and taken as possible evidence for the synthesis of unbihexium. Recent research{{which|date=October 2011}} 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. |
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===Unbiseptium=== |
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Unbiseptium has had one failed attempt at ] in 1978 at the Darmstadt UNILAC accelerator by bombarding a natural ] target with ] ions:<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> |
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:<math>\,^{nat}_{73}\mathrm{Ta} + \,^{136}_{54}\mathrm{Xe} \to \,^{316, 317}\mathrm{Ubs} ^{*} \to \mbox{no atoms}.</math> |
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====Target-projectile combinations leading to Z=127 compound nuclei==== |
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The below table shows various combinations of targets and projectiles leading to compound nuclei with an atomic number of 127. |
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{|class="wikitable" style="text-align:center" |
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! Target !! Projectile !! CN !! Attempt result |
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!<sup>180m</sup>Ta |
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|<sup>136</sup>Xe||<sup>316</sup>Ubs||{{no|Failure to date}} |
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!<sup>181</sup>Ta |
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|<sup>136</sup>Xe||<sup>317</sup>Ubs||{{no|Failure to date}} |
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==See also== |
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* ]: extension of the table beyond the 7th period |
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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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{{Navbox periodic table}} |
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{{Extended periodic table (by Fricke, 32 columns, compact)}} |
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{{DEFAULTSORT:Period 08}} |
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] |
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] |
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] |