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The Element Thorium

[Click for Isotope Data]





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


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).

Thorium's most stable isotope, thorium-232, has a half-life of about 14,050,000,000 years. It decays into radium-228 through alpha decay or decays through spontaneous fission.

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

Electron Shell Configuration:


2s2   2p6

3s2   3p6   3d10

4s2   4p6   4d10   4f14

5s2   5p6   5d10

6s2   6p6   6d2