Thorium

Thorium (symbol: Th) is a member of the actinoid series of chemical elements. Although all isotopes of thorium are 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 tables from before the Second World War often placed thorium as a transition metal.

Discovery

Thorium was first identified in a sample of a new mineral (now called thorite) from the island of Løvø in 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.

Notes and references

Further reading

• Wickleder, Mathias S.; Fourest, Blandine; Dorhout, Peter K. Thorium. In The Chemistry of the Actinide and Transactinide Elements, 3rd ed.; Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean, Eds.; Springer: Dordrecht, the Netherlands, 2006; Vol. 1, Chapter 3, pp 52–160. doi:10.1007/1-4020-3598-5_3, <http://radchem.nevada.edu/classes/rdch710/files/thorium.pdf>.

External links

• WebElements