Thorium
Definition and meaning of Thorium in chemistry.
![Thorium element card: symbol Th, atomic number 90, atomic mass 232.04, electron configuration [Rn] 6d² 7s², oxidation states +4, Actinide, f-block, period 7, solid at room temperature.](/assets/images/terms/thorium-chemical-element.webp)
Thorium is a weakly radioactive metallic element with the symbol Th and atomic number 90. This dense, silvery white actinide metal slowly tarnishes in air and eventually turns black. It is one of the few radioactive elements found abundantly in the Earth's crust.
In more detail
Thorium sits near the beginning of the actinide series on the periodic table. It is actually much more abundant in the Earth's crust than uranium. Miners primarily extract it from rare earth minerals like monazite and thorite.
It has one major natural form, or isotope, known as thorium-232. This specific isotope decays incredibly slowly over a very long period of time. It takes about 14 billion years for half of a sample to disappear.
This long half-life makes its radioactivity extremely weak compared to other similar elements. The pure silvery metal naturally possesses an exceptionally high melting point. Its main compound, thorium dioxide, has one of the highest melting points of any oxide.
Thorium usually has a +4 charge in nearly all of its chemical compounds. This predictable charge helps it form highly stable oxides and halides. Scientists classify thorium as a fertile material rather than a fissile material.
A fissile material can split apart easily to create nuclear energy. A fertile material like thorium must absorb a neutron before it can split. When it absorbs a neutron, it changes into a fissile form of uranium.
This unique ability has sparked global research into new types of nuclear reactors. Many experts hope thorium can provide a sustainable alternative to traditional uranium power plants.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | Th |
| Atomic number | 90 |
| Atomic mass | 232.04 u |
| Category | Actinide |
| State at room temperature | Solid |
Manufacturers previously used thorium dioxide to make gas mantles for portable camping lanterns. A mantle is a small fabric bag that glows brightly over a flame. Thorium was perfect for this application because it produces a brilliant white light. It safely handles the intense heat without melting or breaking down.
Frequently asked questions
Can thorium be used directly to power a nuclear reactor?
No, it cannot power a reactor directly. It must first absorb a neutron to become uranium-233. This new uranium isotope then splits to generate nuclear power.
Is it safe to handle thorium without protective equipment?
Yes, it is generally safe to handle. Its extremely long half-life means it releases radiation very slowly. The external exposure risks are minimal compared to highly radioactive elements.
Related terms
Sources & references
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