Chemistry - Thorium



  • Thorium is one of the radioactive actinide metals that occur naturally in large quantities.

  • The symbol of thorium is ‘Th’ and atomic number is ’90.’

  • In 1829, a Norwegian mineralogist Morten Thrane Esmark, first discovered thorium.

  • Jöns Jacob Berzelius, the Swedish chemist, identified and named it ‘thorium’ after the name of ‘Thor’, the Norse god of thunder.

Salient Features of Thorium

  • Thorium is paramagnetic and soft radioactive actinide metal.

  • Thorium metal’s color is silvery; when it exposed to air, it tarnishes black and form dioxide.

  • All isotopes of thorium are unstable and it is a weak radioactive element.

  • Among all the significant radioactive elements, the half-life of thorium is the longest, i.e. about 14.05 billion years.

  • The melting point of thorium is about 17500C.

Occurrence of Thorium

  • Thorium is primordial element that exists existed in its current form since before the Earth was formed.

  • Thorium, found in the earth’s crust, is refined from the monazite sands.

  • Monazite that occurs in large amounts across the world is the most important source of thorium.

Alloys of Thorium

  • Mag-Thor and thorium-aluminum are the most significant alloys of thorium, Magnesium, and aluminum.

Compounds of Thorium

  • Following are the major compounds of Thorium −

    • Thorium dioxide - ThO2

    • Thorium (IV) sulfide - ThS2

    • Thorium (IV) iodide - ThI4

    • Thorium tetrafluoride - ThF4

    • Thorium (IV chloride - ThCl4

    • Thorium (IV) carbide - ThC

  • Some others are −

    • Thorite

    • Thorium (IV) nitrate

    • Thorium (IV) orthosilicate

Uses of Thorium

  • Thorium is normally used in gas tungsten arc welding (GTAW) because it (thorium) increases the high-temperature strength of tungsten electrodes and accordingly improve arc stability.

  • In electronic equipment, the application of thorium coating on tungsten wire, increases the electron emission of heated cathodes.

  • In chemical industry, the dioxide of thorium namely ‘thoria’ is commonly used.