Thorium

Thorium,  ₉₀Th

General properties
Name, symbol	Thorium, Th
Appearance	Silvery-grey, often black tarnish
Thorium in the periodic table
Ce ↑ Th ↓ Uqq Actinium ← Thorium → Protactinium
Atomic number	90
Standard atomic weight (Ar)	232.0377(4)
Element category	Actinides
Group, block	n/a; f-block
Period	period 7
Electron configuration	[Rn] 6d2 7s2
per shell	2, 8, 18, 32, 18, 10, 2
Physical properties
Silvery-gray
Phase	Solid
Melting point	2023 K ​(1750 °C, ​3182 °F)
Boiling point	5061 K ​(4788 °C, ​8650 °F)
Density near r.t.	11.7 g/cm3
Heat of fusion	13.81 kJ/mol
Heat of	514 kJ/mol
Molar heat capacity	26.23 J/(mol·K)
pressure
Atomic properties
Oxidation states	4, 3, 2, 1 ​(a weakly basic oxide)
Electronegativity	Pauling scale: 1.3
energies	1st: 587 kJ/mol 2nd: 1110 kJ/mol 3rd: 1930 kJ/mol
Atomic radius	empirical: 179.8 pm
Covalent radius	206±6 pm
Miscellanea
Crystal structure	​Face-centred cubic (fcc)
Speed of sound thin rod	2490 m/s (at 20 °C)
Thermal expansion	11 µm/(m·K) (at 25 °C)
Thermal conductivity	54 W/(m·K)
Electrical resistivity	157 Ω·m (at 0 °C)
Magnetic ordering	Paramagnetic
Young's modulus	79 GPa
Shear modulus	31 GPa
Bulk modulus	54 GPa
Poisson ratio	0.27
Mohs hardness	3.0
Vickers hardness	295–685 MPa
Brinell hardness	390–1500 MPa
CAS Registry Number	7440-29-1
History
Naming	After Thor, the Norse god of thunder
Discovery	Jöns Jakob Berzelius (1829)

Thorium is a chemical element with the symbol Th and atomic number 90.

Properties

Chemical

Thorium is a highly reactive metal. At room temperature, thorium is slowly attacked by water but does not readily dissolve in most common acids, the exception being hydrochloric acid. It will dissolve in concentrated nitric acid containing a small amount of catalytic fluoride or fluorosilicate ions. At high temperatures, it is easily attacked by oxygen, hydrogen, nitrogen, the halogens, and sulfur. Finely divided thorium is highly pyrophoric. Thorium burns with a bright white flame in the air.

Physical

Thorium is a soft, paramagnetic, bright silvery radioactive actinide metal. Pure thorium is soft, very ductile. Because thorium melts at 1750 °C and boils at 4788 °C, it has one of the widest liquid range of all metals.

Availability

Thorium was available in the past as thorium dioxide in gas mantles. Certain heat resistant ceramics contain thoria. Small amounts of thorium are added in TIG welding rods. Old gas mantles can contain amounts of thorium dioxide.

The acquisition of pure metal is problematic, as there are almost no companies that will sell very small samples to individuals. Element collector Max Whitby explained in a YT video that there are extremely few companies that will sell small samples of thorium, even chemical lab suppliers. He also discovered that shipping it outside requires a heavy-duty license for radioactive materials, as he discovered when he was visited by authorities.

Isolation

Metallic thorium can be extracted by reducing thorium dioxide with calcium in an inert atmosphere:

ThO₂ + 2 Ca → 2 CaO + Th

Dissolving TIG welding rods in acids or alkali is difficult, as tungsten is very resistant to most reagents, and bulk metal is even more inert. However, one can successfully dissolve them in concentrated H₂O₂, which forms tungstic acid and ThO₂.

Projects

• Thorium halides
• Make thorium dioxide
• Firestarters

Handling

Safety

Thorium is highly reactive and pyrophoric. It is only mildly radioactive (²³²Th has a half-life of 14.05 billion years and is alpha radioactive), the radiation is too weak to penetrate the skin. Soluble thorium compounds are toxic and should be handled with proper protection.

Bulk thorium is difficult to ignite, but finely divided metal is highly pyrophoric.

Storage

As thorium will slowly react with the air, it should be stored under oil or under an inert atmosphere, in a container. Sealing it is not necessary. Being weak radioactive, thorium does not require radiation shielding (the storage container walls will effectively absorb the weak alpha radiation).

Disposal

Thorium and its compounds, are toxic, and it is recommended to avoid dumping the compounds in the environment and instead should be taken to waste disposal facilities.

If the thorium was extracted from its natural ore that was taken from an area where the said ore can be easily collected, it's not entirely a bad idea to dispose of the ore wastes as well as thorium compounds residues in the said area, as the said area is already naturally contaminated and radioactive and the amount of ore waste is (almost) the same as the one you originally picked it up.

References

Relevant Sciencemadness threads

• The trials and tribulations of Thorium production
• Thorium Separation From TIG Electrodes
• Thorium from monazite sand