PTL:Thorium
From ChemEd Collaborative
Thorium is the second member of the actinide series of elements, which stretches from actinium (Ac) to lawrencium (Lr).
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Discovered
The Reverend Hans Morten Thrane Esmark (1802-1882) sent the great Swedish chemist Berzelius what he took to be a new mineral containing tantalum. However, in 1829 Berzelius found that it was in fact a silicate of a new element,
Name
which he named thorium in honor of the Norse god Thor.
Characteristics
Pure thorium metal is bright and silvery. It has a relatively high density (11.72 g/cc) and is very high melting (1750°C). It is also weaker than structural metals and softer than steel.
Prepared
The metal is obtained by reduction of the oxide or fluoride with calcium or potassium.
ThO2(s) + Ca(s) 
Th(s) + 2 CaO(s)
Found
Thorium is not a very rare element, since it comprises 0.001-0.002% of the earth's crust. In fact, it is roughly twice as abundant as tin, a commercially important metal. Its chief source is the mineral monazite [(Ce,Y,La,Nd,Th)PO4], a phosphate of thorium and lanthanide elements.
Emission Spectra
This is the emission spectra for Thorium.
Reactions
Thorium is very reactive chemically. It is attacked by oxygen to give thorium(IV) oxide, ThO2 and reacts with HCl but not with nitric acid.
The element has at least 25 isotopes. All are radioactive, but only three have relatively long half-lives. Thorium--232 decays by alpha emission with a half life of 14,100,000,000 years.
Uses
Although mildly radioactive, thorium(IV) oxide is used commercially in the [mantles of gas lamps and in lamp filaments]. When heated by even a weak flame, the refractory oxide emits a brilliant white light.
The main commercial interest in thorium has been as a fuel in breeder reactors. The reason for this is that it has been known for some time that the product of neutron absorption by thorium is 233U, which undergoes fission even by slow or low energy neutrons. It is thought that there is more energy available for use from thorium in the earth's minerals than from uranium and fossil fuels.
Much of the heat within the earth is thought to come from the radioactive decay of thorium and uranium.
A more recently discovered use of thorium is as an alloying agent with magnesium, which leads to considerably greater strength of the light weight magnesium. The oxide is also a common ingredient in high-quality lenses.
