The Element Thorium
Atomic Number: 90
Atomic Weight: 232.0377
Melting Point: 2023 K (1750°C or 3182°F)
Boiling Point: 5061 K (4788°C or 8650°F)
Density: 11.72 grams per cubic centimeter
Phase at Room Temperature: Solid
Element Classification: Metal
Period Number: 7
Group Number: none
Group Name: Actinide
Special Notes: Radioactive
What's in a name? Named for the Scandinavian god of war, Thor.
Say what? Thorium is pronounced as THOR-ee-em or as THO-ree-em.
History and Uses:
Thorium was discovered by Jöns Jacob Berzelius, a Swedish chemist, in 1828. He discovered it in a sample of a mineral that was given to him by the Reverend Has Morten Thrane Esmark, who suspected that it contained an unknown substance. Esmark's mineral is now known as thorite (ThSiO4). Thorium makes up about 0.0007% of the earth's crust and is primarily obtained from thorite, thorianite (ThO2) and monazite ((Ce, La, Th, Nd, Y)PO4).
Thorium is used as an alloying agent to improve magnesium's strength at high temperatures. Thorium is also used to coat tungsten filaments used in electronic devices, such at television sets. When bombarded with neutrons, thorium-232 becomes thorium-233, which eventually decays into uranium-233 through a series of beta decays. Uranium-233 is a fissionable material and can be used as a nuclear fuel.
Thorium oxide (ThO2), one of thorium's compounds, has many uses. It is primarily used in a type of lantern mantel known as a Welsbach mantle. This mantle, which also contains about 1% cerium oxide, glows with a bright white light when it is heated in a gas flame. Thorium oxide has a very high melting point, about 3300°C, and is used to make high temperature crucibles. Thorium oxide is also used to make glass with a high index of refraction that is used to make high quality camera lenses. Thorium oxide is used as a catalyst in the production of sulfuric acid (H2SO4), in the cracking of petroleum products and in the conversion of ammonia (NH3) to nitric acid (HNO3).
Estimated Crustal Abundance: 9.6 milligrams per kilogram
Estimated Oceanic Abundance: 1×10-6 milligrams per liter
Number of Stable Isotopes: 0 (View all isotope data)
Ionization Energy: 6.08 eV
Oxidation States: +4
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d10
6s2 6p6 6d2