Discovery date : 1829
Discovered by: Jöns Jacob Berzelius
Origin of the name: Thorium is named after Thor, the Scandinavian god of war.
Allotropes : -
~>THORIUM is a weakly radioactive metallic chemical element with symbol Th and atomic number 90. Thorium metal is silvery and tarnishes black when it is exposed to air, forming the dioxide; it is moderately hard, malleable, and has a high melting point. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state; it is quite reactive and can ignite in air when finely divided.
| FACT BOX | |||
| Group | Actinides | Melting point | 1750°C, 3182°F, 2023 K |
| Period | 7 | Boiling point | 4785°C, 8645°F, 5058 K |
| Block | f | Density (g cm−3) | 11.7 |
| Atomic number | 90 | Relative atomic mass | 232.038 |
| State at 20°C | Solid | Key isotopes | 230Th,232Th |
| Electron configuration | [Rn] 6d27s2 | CAS number | 7440-29-1 |
| ChemSpider ID | 22399 | ChemSpider is a free chemical structure database | |
In 1829, Jöns Jakob Berzelius of the Royal Karolinska Institute, Stockholm extracted thorium from a rock specimen sent to him by an amateur mineralogist who had discovered it near Brevig and realised that it had not previously been reported. The mineral turned out to be thorium silicate, and it is now known as thorite. Berzelius even produced a sample of metallic thorium by heating thorium fluoride with potassium, and confirmed it as a new metal.
The radioactivity of thorium was first demonstrated in 1898 by Gerhard Schmidt and confirmed by Marie Curie. Thorium, like uranium, survives on Earth because it has isotopes with long half-lives, such as the predominant one, thorium-232, whose half life is 14 billion years.