Symbol: Th
Atomic number: 90
Category: actinides
Group: n/a
Period: 7
Block: f
Atomic weight: 232.0381 g/mol
Electrons per shell: 2, 8, 18, 32, 18, 10, 2
CAS number: 7440-29-1
Phase: solid
Density: 11.7 kg/dm3 (near room temperature)
Melting point: 2115 K (1842 C, 3348 F)
Boiling point: 5061 K (4788 C, 8650 F)
Crystal structure: cubic face centered
Oxidation states: 4
Electronegativity: 1.3 (Pauling scale)
Name's origin: Thor
Name's meaning: the Norse god of thunder - the element was discovered in Norway
- is a silvery-white metal which is air-stable and retains its luster for several months
- when contaminated with the oxide, thorium slowly tarnishes in air, becoming gray and finally black
- is soft, very ductile, and can be cold-rolled, swaged, and drawn
- powdered thorium metal is often pyrophoric and should be carefully handled
- is used e.g. as an alloying agent in magnesium, in uranium-thorium age dating and as a radiation shield
- is found in small amounts in most rocks and soils, where it is about four times more abundant than uranium, and is about as common as lead
- decays very slowly compared to many other radioactive materials, and the alpha radiation emitted cannot penetrate human skin
- owning and handling small amounts of thorium, such as a gas mantle, is considered safe if care is taken not to ingest the thorium - lungs and other internal organs can be penetrated by alpha radiation
- exposure to an aerosol of thorium can lead to increased risk of cancers of the lung, pancreas and blood