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thorium (Th)





A silvery-white radioactive metallic element , one of the actinides. Its chief ore is monazite. Thorium is tetravalent, resembling zirconium and hafnium. It is used in magnesium alloys and to produce uranium-233 for atomic fuel.

Thorium has 13 radioactive isotopes only one of which, thorium-232, occurs naturally.

The refractory thorium (IV) oxide was used to make incandescent gas mantles; it is added in small amounts to the tungsten filaments in electric lights.


atomic number 90
relative atomic mass 232.04
relative density 14.66
melting point 1,700°C (3,100°F)
boiling point 4,000°C (7,200°F)


Related categories

   • ATOMIC AND NUCLEAR PHYSICS
   • INORGANIC CHEMISTRY