Editing Period 7 element (section)

=== Transactinides ===
{{main|Transactinide elements}}
''Transactinide elements'' (also, '''transactinides''', or '''super-heavy elements''', or '''superheavies''') are the [[chemical element]]s with [[atomic number]]s greater than those of the [[actinide]]s, the heaviest of which is [[lawrencium]] (103).<ref>[http://www.iupac.org/reports/provisional/abstract04/connelly_310804.html IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004)] {{webarchive|url=https://web.archive.org/web/20061027174015/http://www.iupac.org/reports/provisional/abstract04/connelly_310804.html |date=2006-10-27 }} (online draft of an updated version of the "''Red Book''" IR 3–6)</ref><ref>{{cite book |editor1-first=Lester R. |editor1-last=Morss |editor2-first=Norman M. |editor2-last=Edelstein |editor3-first=Jean |editor3-last=Fuger |title=The Chemistry of the Actinide and Transactinide Elements |edition=3rd |year=2006 |publisher=Springer |location=Dordrecht, The Netherlands |isbn=978-1-4020-3555-5}}</ref> All transactinides of period 7 have been discovered, up to [[oganesson]] (element 118).

Superheavies are also [[transuranic element]]s, that is, have atomic number greater than that of [[uranium]] (92). The further distinction of having an atomic number greater than the actinides is significant in several ways:
*The transactinide elements all have electrons in the 6d [[Electron subshell|subshell]] in their ground state (and thus are placed in the [[d-block]]).
*Even the longest-lived known isotopes of many transactinides have extremely short half-lives, measured in seconds or smaller units.
*The [[element naming controversy]] involved the first five or six transactinides. These elements thus used three-letter [[Systematic element name|systematic names]] for many years after their discovery was confirmed. (Usually, the three-letter symbols are replaced with two-letter symbols relatively soon after a discovery has been confirmed.)

Transactinides are [[radioactive]] and have only been obtained synthetically in laboratories. None of these elements has ever been collected in a macroscopic sample. Transactinides are all named after scientists, or important locations involved in the synthesis of the elements.

Chemistry Nobel Prize winner [[Glenn T. Seaborg]], who first proposed the [[actinide concept]] which led to the acceptance of the [[actinide series]], also proposed the existence of a transactinide series ranging from element 104 to 121 and a [[superactinide series]] approximately spanning elements 122 to 153. The transactinide [[seaborgium]] is named in his honor.

IUPAC defines an element to exist if its lifetime is longer than 10{{sup|−14}} second, the time needed to form an electron cloud.<ref>{{Cite web | url=http://www.kernchemie.de/Transactinides/Transactinide-2/transactinide-2.html | title=Kernchemie}}</ref>