Molecular Structure:

Molecular Formula: Th
Molecular Weight: 232.0381
IUPAC Name: Thorium
Synonyms of Thorium (CAS NO.7440-29-1): 232Th ; EINECS 231-139-7 ; HSDB 864 ; Thorium-232 ; Thorium metal, pyrophoric ; Thorium metal, pyrophoric [UN2975] [Radioactive] ; Thorium-232 and its decay products, dministered intravenously as a colloidal dispersion of 232ThO2 ; UN2975
CAS NO: 7440-29-1
Classification Code:  2007 CERCLA Priority List, Rank: 101
Density: 1.03 g/mL at 25 °C

     M. T. Esmark found a black mineral on a  Island, Norway and gave a sample to Professor Jens Esmark, a noted mineralogist who was not able to identify it, so he sent a sample to the Swedish chemist Jons Jakob Berzelius for examination in 1828.
    Berzelius analyzed it and named it after Thor, the Norse god of thunder. The metal had virtually no uses until the invention of the gas mantle in 1885.
    The crystal bar process (or Iodide process) was discovered by Anton Eduard van Arkel and Jan Hendrik de Boer in 1925 to produce high-purity metallic thorium.
    The name ionium was given early in the study of radioactive elements to the 230Th isotope produced in the decay chain of 238U before it was realized that ionium and thorium were chemically identical. The symbol Io was used for this supposed element.   

Reported in EPA TSCA Inventory.

Hazard Codes of Thorium (CAS NO.7440-29-1): T
Risk Statements: 23/24/25-34 
R23/24/25: Toxic by inhalation, in contact with skin and if swallowed. 
R34: Causes burns.
Safety Statements: 26-27-28-36/37/39-45 
S26: In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. 
S27: Take off immediately all contaminated clothing. 
S28: After contact with skin, wash immediately with plenty of soap-suds. 
S36/37/39: Wear suitable protective clothing, gloves and eye/face protection. 
S45: In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.)
RIDADR: UN 3264 8/PG 3
HazardClass: 7
PackingGroup: Commercial
Suspected carcinogen. Taken internally as ThO₂, it has proven to be carcinogenic due to its radioactivity. On an acute basis it has caused dermatitis. Flammable in the form of dust when exposed to heat or flame, or by chemical reaction with oxidizers. The powder may ignite spontaneously in air. Potentially hazardous reactions with chlorine, fluorine, bromine, oxygen, phosphorus, silver, sulfur, air, nitryl fluoride, peroxyformic acid.

DOT Classification:  7; Label: RADIOACTIVE, SPONT Combustible

    Thorium (CAS NO.7440-29-1) is slowly attacked by water, but does not dissolve readily in most common acids, except hydrochloric. It dissolves in concentrated nitric acid containing a small amount of catalytic fluoride ion.Thorium is dimorphic, changing at 1400 °C from a face-centered cubic to a body-centered cubic structure. 
    Pure thorium is a silvery-white metal which is air-stable and can retains its luster for several months. Pure thorium is soft, very ductile, and can be cold-rolled, swaged, and drawn,and  often contain several tenths of a percent of the oxide. 
    Powdered thorium metal is often pyrophoric and should be carefully handled. When heated in air, thorium metal turnings ignite and burn brilliantly with a white light. Thorium has the largest liquid range of any element: 2946 °C between the melting point and boiling point.
    If thorium is contaminated with the oxide, it will  slowly tarnishes in air, becoming gray and finally black.