An Overview about the Chemical Element Thorium


Symbol: Th

Atomic Number: 90

Atomic Mass: 232.0381 amu (atomic mass units)

Melting Point: 1750.0 C (2023.15 K, 3182.0 F)

Boiling Point: 4790.0 C (5063.15 K, 8654.0 F)

Number of Protons: 90

Number of Electrons: 90

Number of Neutrons: 142

Classification: Rare Earth Metal

Crystal Structure: Cubic

Density @ 293 K: 11.72 grams per cubic centimeter

Color: Silver

In 1828 the Swedish chemist Jons Jacob Berzelius working on a mineral sample given to him by the Reverend Has Morten Thrane Esmark discovered a new element. The element was given the name thorium after Thor the god of war from Scandinavian legend. The mineral that it was originally isolated from is now known as thorite. In addition to thorite thorium is extracted in commercially viable amounts from the mineral thorianite and monazite sands

Thorium is a rare earth element of the actinide or actinoid series. It is one of only four naturally occurring actinides. The other three naturally occurring actinides are uranium, actinium and protactinium.

It has been estimated that there is more energy stored within the thorium present in the rocks forming earth’s crust than in the total of the fossil fuel and uranium reserves. The heat produced within the earth’s mantle is thought to be mainly derived from thorium and uranium.

All of thorium’s isotopes are unstable. Thorium-232 makes up the total of the naturally occurring thorium and has a half life of 14,050,000,000 years. It undergoes a series of alpha decays to become radium-228. There are nearly 30 man-made isotopes of Thorium currently identified. Thorium-218 has the shortest half life of them all at 109 nanoseconds.

Thorium is a silvery metal which is air-stable. As such it retains its luster for several months. If thorium is contaminated with thorium oxide then it will tarnish slowly in air first becoming grey before turning black. Thorium oxide has a high melting point 3300 C (3272 K, 5970 F). This is the highest melting point of all oxides of any element. Very few elements or compounds have melting points in excess of 3000 C

(3573 K, 5432 F); the element tungsten does as does the compound tantalum carbide.

Thorium does not dissolve readily in most acids with the exception of hydrochloric acid. It is attacked slowly by water. Shavings or powdered thorium can ignite in air when heated and will burn with a bright white flame.

There are a number of uses for thorium metal

* Uses as alloying agent thorium will improve the strength of magnesium at high temperatures.

* Thorium can be coated on to the tungsten filaments which are used in a variety of electronic equipment such as televisions.

* If it is bombarded with neutrons thorium-232 becomes the isotope thorium-233 this will decay in a series of beta decays to form uranium-233 which can be used as a nuclear fuel.

Thorium oxide also has a number of very valuable uses.

* It is used in the production of the Welsbach mantle. This lantern mantle will glow with a very bright white light if it is heated by a gas flame. The Welsbach mantle also contains 1% cerium oxide.

* It is used to manufacture crucibles used at high temperatures.

* Thorium oxide can produce glass with a high refractive index which is suitable for the manufacture of high quality lenses for cameras.

* Thorium oxide is used as a catalyst in a number of industries such as a catalyst in sulfuric acid production, petroleum cracking and the conversion of ammonia into nitric acid.