View source for Thorium

{{Infobox element
|name = thorium
|symbol = Th
|left = [[actinium]]
|right = [[protactinium]]
|above = [[Cerium|Ce]]
|below = —
|atomic-number = 90
|configuration = [Rn] 6d<sup>2</sup> 7s<sup>2</sup>
|phys-ref = <ref name="WFD">{{citation | last1 = Wickleder | first1 = Mathias S. | last2 = Fourest | first2 = Blandine | last3 = Dorhout | first3 = Peter K. | contribution = Thorium | title = The Chemistry of the Actinide and Transactinide Elements | editor1-first = Lester R. | editor1-last = Morss | editor2-first = Norman M. | editor2-last = Edelstein | editor3-first = Jean | editor3-last = Fuger | edition = 3rd | year = 2006 | volume = 1 | publisher = Springer | location = Dordrecht, the Netherlands | chapter = 3 | pages = 52–160 | url = http://radchem.nevada.edu/classes/rdch710/files/thorium.pdf | doi = 10.1007/1-4020-3598-5_3}}.</ref><ref name="G&E">{{Greenwood&Earnshaw1st|pages=1450–86}}.</ref>
|melting-point = 1750&nbsp;°C (2023&nbsp;K)
|boiling-point = 4850&nbsp;°C (5123&nbsp;K)
|density = 11.72 g cm<sup>−3</sup>
|resistivity = 15.7{{e|−6}} Ω cm
|chem-ref = 
|electronegativity = 
|IE-ref = <ref>{{citation | last1 = Köhler | first1 = S. | last2 = Deißenberger | first2 = R. | last3 = Eberhardt | first3 = K. | last4 = Erdmann | first4 = N. | last5 = Herrmann | firat5 = G. | last6 = Huber | first6 = G. | last7 = Kratz | first7 = J. V. | last8 = Nunnemann | first8 = M. | last9 = Passler | first9 = G. | last10 = Rao | first10 = P. M. | last11 = Riegel | first11 = J. | last12 = Trautmann | first12 = N. | last13 = Wendt | first13 = K. | year = 1997 | title = Determination of the first ionization potential of actinide elements by resonance ionization mass spectroscopy  | journal = Spectrochim. Acta, Part B | volume = 52 | issue = 6 | pages = 717–26 | doi = 10.1016/S0584-8547(96)01670-9}}.</ref>
|IE1 = 6.3067(2) eV<br/>608.50(2) kJ mol<sup>−1</sup>
|IE2 = 
|IE3 = 
|EA-ref = 
|EA1 = 
|thermo-ref = <ref name="WFD"/><ref name="NIST">{{NIST chemistry | name = Thorium | id = 1S/Th | accessdate = 2011-01-10}}.</ref>
|entropy = 51.8(5) J K<sup>−1</sup> mol<sup>−1</sup>
|enthalpy-vaporization = 602(6) kJ mol<sup>−1</sup>
|enthalpy-atomization = 
|entropy-atomization = 
|enthalpy-fusion = 14 kJ mol<sup>−1</sup>
|radius-ref = <ref name="WFD"/><ref>{{Cordero et al. (2008)}}.</ref><ref>{{Shannon (1976)}}.</ref>
|metallic-radius = 180 pm
|covalent-radius = 206 pm
|ionic-radius = 108 pm (Th<sup>4+</sup>, ''O<sub>h</sub>'')
|CAS-number = 7440-29-1
|EC-number = 231-139-7
|StdInChIkey = ZSLUVFAKFWKJRC-UHFFFAOYSA-N
}}
'''Thorium''' (symbol: '''Th''') is a member of the [[actinoid]] series of [[chemical element]]s. Although all [[isotope]]s of thorium are [[Radioactivity|unstable]], [[thorium-232]] has a sufficiently long [[half-life]] (14 billion years) that a substantial amount of primordial thorium has survived since the formation of the Solar System. The natural material is only very slightly radioactive, and thorium and its compounds have a number of commercial uses, although some precautions must be taken over its decay products.

Thorium was identified as a new element in 1828, and named after Thor, the Norse god of strength. Its chemistry resembles that of [[zirconium]] and [[hafnium]], with a preponderance of the +4 [[oxidation state]], and [[periodic table]]s from before the Second World War often placed thorium as a [[transition metal]].

==Discovery and history==
Thorium was first identified in a sample of a new mineral (now called [[thorite]]) from the island of Løvøy in Vestfold, Norway. The sample was collected by the Lutheran pastor and amateur mineralogist Hans Morten Thrane Esmark; unable to identify it, he sent it to Christiana (modern-day Oslo) where his father Jens Esmark was professor of mineralogy and geology at the university. When Esmark Sr. had no more success than his son, he passed the sample on to the reknowned Swedish chemist [[Jöns Jacob Berzelius]], who correctly ascertained that the mineral contained a new chemical element.<ref>{{citation | first = J. J. | last = Berzelius | authorlink = Jöns Jacob Berzelius | title = Ueber den Thorit, ein neues Mineral, und eine darin enthaltene neue Erde, die Thorerde | journal = Ann. Phys. Chem. | year = 1829 | volume = 91 | issue = 4 | pages = 633–34 | doi = 10.1002/andp.18290910412}}.</ref><ref>{{citation | last = Berzelius | first = J. J. | authorlink = Jöns Jacob Berzelius | year = 1829 | title = Undersökning af ett nytt mineral (Thorit), som innehåller en förut obekant jord | journal = K. Sven. Vetenskapsakad. Handl. | volume = 9 | pages = 1–30}}; {{citation | title = Untersuchung eines neuen Minerals und einer darin enthaltenen zuvor unbekannten Erde | journal = Ann. Phys. Chem. | year = 1829 | volume = 92 | issue = 7 | pages = 385–415 | doi = 10.1002/andp.18290920702}}.</ref>

Thorium remained something of a curiosity until the invention of the incandescent gas mantle in 1885 by [[Carl Auer von Welsbach]].

==Occurance and extraction==

==Notes and references==
===Notes===
{{reflist|group=note}}

===References===
{{reflist}}

==External links==
{{wikipedia|Thorium}}
*[http://www.webelements.com/thorium/ WebElements]

[[Category:Thorium| ]]
[[Category:Chemical elements]]
[[Category:Actinoids]]