Editing Thorium (section)

===Discovery===
In 1828, [[Morten Thrane Esmark]] found a black mineral on [[Løvøya, Telemark|Løvøya]] island, [[Telemark]] county, Norway. He was a Norwegian [[priest]] and amateur [[mineralogist]] who studied the minerals in Telemark, where he served as [[vicar]]. He commonly sent the most interesting specimens, such as this one, to his father, [[Jens Esmark]], a noted mineralogist and professor of mineralogy and geology at the [[Royal Frederick University]] in Christiania (today called [[Oslo]]).<ref name="snl">{{cite encyclopedia|year=2007|title=Morten Thrane Esmark|encyclopedia=[[Store norske leksikon]]<!--|editor-last=Henriksen |editor-first=P. is this correct? -->|first=R. S.|last=Selbekk|publisher=[[Kunnskapsforlaget]]|url=http://www.snl.no/Morten_Thrane_Esmark|access-date=16 May 2009|language=no|archive-date=28 April 2021|archive-url=https://web.archive.org/web/20210428144944/https://snl.no/Morten_Thrane_Esmark|url-status=live}}</ref> The elder Esmark determined that it was not a known mineral and sent a sample to Berzelius for examination. Berzelius determined that it contained a new element.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=52–53}} He published his findings in 1829, having isolated an impure sample by reducing {{chem2|K[ThF5]}} (potassium pentafluorothorate(IV)) with [[potassium]] metal.<ref name="Weeks" /><ref>{{cite journal|last=Berzelius|first=J. J.|language=de|date=1829|url=http://gallica.bnf.fr/ark:/12148/bpt6k151010.pleinepage.r=Annalen+der+Physic.f395.langFR|title=Untersuchung eines neues Minerals und einer darin erhalten zuvor unbekannten Erde|trans-title=Investigation of a new mineral and of a previously unknown earth contained therein|journal=Annalen der Physik und Chemie|volume=16|pages=385–415|doi=10.1002/andp.18290920702|bibcode=1829AnP....92..385B|issue=7|archive-date=27 April 2021|access-date=20 July 2009|archive-url=https://web.archive.org/web/20210427143538/https://gallica.bnf.fr/ark:/12148/bpt6k151010.pleinepage.r=Annalen+der+Physic.f395.langFR|url-status=live}} (modern citation: ''Annalen der Physik'', vol. 92, no. 7, pp. 385–415).</ref><ref>{{cite journal|last=Berzelius |first=J. J. |date= 1829|title=Undersökning af ett nytt mineral (Thorit), som innehåller en förut obekant jord |trans-title=Investigation of a new mineral (thorite), as contained in a previously unknown earth|journal=Kungliga Svenska Vetenskaps Akademiens Handlingar |pages=1–30 |language=sv}}</ref> Berzelius reused the name of the previous supposed element discovery<ref name="Weeks">{{cite journal |doi= 10.1021/ed009p1231|bibcode= 1932JChEd...9.1231W |title= The discovery of the elements. XI. Some elements isolated with the aid of potassium and sodium: Zirconium, titanium, cerium, and thorium |date= 1932 |last1= Weeks |first1= M. E. |author-link1=Mary Elvira Weeks| journal= Journal of Chemical Education |volume= 9 |issue= 7 |page= 1231}}</ref><ref>{{cite journal |doi= 10.1002/ange.19020153703 |title= Die eigentlichen Thorit-Mineralien (Thorit und Orangit) |trans-title= The actual thoritic minerals (thorite and orangite) |language= de |date= 1902 |last1= Schilling |first1= J. |journal= Zeitschrift für Angewandte Chemie |volume= 15 |issue= 37 |pages= 921–929 |bibcode= 1902AngCh..15..921S |url= https://zenodo.org/record/1424433 |archive-date= 13 April 2023 |access-date= 24 August 2019 |archive-url= https://web.archive.org/web/20230413111147/https://zenodo.org/record/1424433 |url-status= live }}</ref> and named the source mineral thorite.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=52–53}}

[[File:J J Berzelius.jpg|thumb|upright|alt=Jöns Jacob Berzelius|[[Jöns Jacob Berzelius]], who first identified thorium as a new element]]

Berzelius made some initial characterisations of the new metal and its chemical compounds: he correctly determined that the thorium–oxygen mass ratio of thorium oxide was 7.5 (its actual value is close to that, ~7.3), but he assumed the new element was divalent rather than tetravalent, and so calculated that the atomic mass was 7.5 times that of oxygen (120 [[atomic mass unit|amu]]); it is actually 15 times as large.{{efn|At the time, the [[rare-earth element]]s, among which thorium was found and with which it is closely associated in nature, were thought to be divalent; the rare earths were given [[atomic weight]] values two-thirds of their actual ones, and thorium and uranium are given values half of the actual ones.}} He determined that thorium was a very [[Electronegativity#Electropositivity|electropositive]] metal, ahead of cerium and behind zirconium in electropositivity.<ref name="leach2">{{cite web |url=http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=453 |title=The Internet Database of Periodic Tables: Berzelius' Electronegativity Table |last=Leach |first=M. R. |access-date=16 July 2016 |archive-date=28 April 2021 |archive-url=https://web.archive.org/web/20210428202351/https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=453 |url-status=live }}</ref> Metallic thorium was isolated for the first time in 1914 by Dutch entrepreneurs Dirk Lely Jr. and Lodewijk Hamburger.{{efn|The main difficulty in isolating thorium lies not in its chemical electropositivity, but in the close association of thorium in nature with the rare-earth elements and uranium, which collectively are difficult to separate from each other. Swedish chemist [[Lars Fredrik Nilson]], the discoverer of scandium, had previously made an attempt to isolate thorium metal in 1882, but was unsuccessful at achieving a high degree of purity.<ref>{{cite journal |last=Nilson |first=L. F. |date=1882 |title=Über metallisches Thorium |trans-title=About metallic thorium |journal=Berichte der Deutschen Chemischen Gesellschaft |volume=15 |issue=2 |pages=2537–2547 |doi=10.1002/cber.188201502213 |language=de |url=https://zenodo.org/record/1425272 |archive-date=13 April 2023 |access-date=24 August 2019 |archive-url=https://web.archive.org/web/20230413114159/https://zenodo.org/record/1425272 |url-status=live }}</ref> Lely and Hamburger obtained 99% pure thorium metal by reducing thorium chloride with sodium metal.<ref name="Meister" /> A simpler method leading to even higher purity was discovered in 1927 by American engineers John Marden and Harvey Rentschler, involving the reduction of thorium oxide with calcium in presence of calcium chloride.<ref name="Meister">{{cite report |year=1948 |last=Meister |first=G. |url=http://www.lm.doe.gov/Considered_Sites/F/Foote_Mineral_Co_-_PA_27/PA_27-3.pdf |title=Production of Rarer Metals |publisher=[[United States Atomic Energy Commission]] |access-date=22 September 2017 |archive-date=24 February 2017 |archive-url=https://web.archive.org/web/20170224180301/https://www.lm.doe.gov/Considered_Sites/F/Foote_Mineral_Co_-_PA_27/PA_27-3.pdf }}</ref>}}