Thorium (Th)


  • Symbol: Th
  • Atomic Number: 90
  • Atomic Weight: 232.03806
  • Element Classification: Actinide
  • Discovered By: Jöns Jacob Berzelius
  • Discovery Date: 1828
  • Name Origin: Named after Thor, the Norse god of thunder
  • Density(g/cc): 11.7
  • Melting Point: 1750°C
  • Boiling Point: 4788°C
  • Appearance: Silvery, often with a black tarnish when exposed to air
  • Atomic Radius(pm): 180


Thorium was discovered in 1828 by the Swedish chemist Jöns Jacob Berzelius. The discovery came from an analysis of a sample of a mineral sent to him by the mineralogist Jens Esmark, who had found it in Løvøya, Norway. Berzelius isolated a new silvery white metal and named it thorium after Thor, the Norse god of thunder, reflecting the element’s power and the Scandinavian mythology.

Relation to Other Elements

Thorium is a member of the actinide series, elements known for their radioactive properties and filling of the 5f electron shell. It shares similar chemical properties with other actinides but is somewhat unique due to its stability among them; thorium-232, its most stable and abundant isotope, has a half-life of about 14.05 billion years. Thorium is somewhat more abundant in the Earth’s crust than uranium, making it of interest as a potential nuclear fuel.

Natural Occurrence

Thorium is naturally occurring and is relatively abundant in the Earth’s crust, found in small amounts in most rocks and soils. It occurs in several minerals, the most significant being monazite and thorite, from which commercial thorium can be extracted. Thorium is more abundant than uranium and is considered an underutilized resource for nuclear energy.


Thorium has several applications, leveraging its radioactive properties and abundance:

  • Nuclear Energy: Thorium is considered a potential alternative to uranium for nuclear fuel due to its abundance and the possibility to breed uranium-233, a fissile material, from thorium-232. Thorium reactors, though not yet widely adopted, promise several advantages, including reduced waste and enhanced safety.
  • Gas Mantles: Historically, thorium was used in the manufacture of gas mantles for portable gas lights, as it emits a bright white light when heated. This use has declined due to health concerns related to radioactivity.
  • Materials Science: Thorium is used as an alloying agent in magnesium, imparting greater strength and high-temperature resistance to the metal, useful in aerospace applications.
  • Radiation Shields: Due to its high density and radioactivity, thorium can be used in radiation shielding materials.

The discovery and exploration of thorium’s properties have highlighted its potential as a safer and more abundant alternative for nuclear energy. Ongoing research into thorium-based nuclear reactors aims to harness this potential, addressing challenges related to technology, economics, and nuclear proliferation.

Actinium (Ac)

Protactinium (Pa)