Thorium
Definition and meaning of Thorium in chemistry.
Thorium is a weakly radioactive metallic element designated by the symbol Th and atomic number 90. It is a dense, silvery white actinide metal that tarnishes slowly when exposed to air, eventually turning black. Thorium is considered one of the few radioactive elements that exist in substantial quantities in the Earth crust.
In more detail
Positioned early in the actinide series of the periodic table, thorium is notably more abundant in the Earth crust than uranium and is primarily extracted from rare earth minerals such as monazite and thorite. It features a single major natural isotope, thorium-232, which decays incredibly slowly with a half-life of roughly 14 billion years, rendering its specific radioactivity exceptionally weak compared to other actinides. The pure silvery metal possesses an exceptionally high melting point, and its compound thorium dioxide boasts one of the highest melting points of all known oxides. Thorium chemistry is heavily characterized by a dominant +4 oxidation state in nearly all its chemical compounds, forming highly stable oxides and halides. It is classified as a fertile rather than fissile material, meaning it can absorb a neutron to eventually transmute into the fissile isotope uranium-233. This unique transmutation capability has driven extensive global research into developing closed thorium based nuclear fuel cycles as a sustainable alternative to conventional uranium reactors.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | Th |
| Atomic number | 90 |
| Atomic mass | 232.04 u |
| Category | Actinide |
| State at room temperature | Solid |
| Melting point | 1750 degrees Celsius |
| Boiling point | 4788 degrees Celsius |
Thorium dioxide was previously used extensively in gas mantles for portable camping lanterns because it produces a brilliant white light when heated by a flame.
Frequently asked questions
Can thorium be used directly to power a nuclear reactor?
No, it must first be used as a fertile fuel in an advanced reactor to produce uranium-233, which then undergoes nuclear fission to generate power.
Is it safe to handle thorium without protective equipment?
Due to its extremely long half-life, its specific radioactivity is very low, making external exposure risks relatively minimal compared to highly radioactive elements.