thorium

Name thorium
Symbol Th
Atomic Weight 232.0381
Atomic Number 90
CAS ID 7440-29-1
Group Number
Group Name Actinoid
Period Number 7
Origin of Name Named after Thor, Scandinavian god of war.
Year Discovered 1815
Discovery Credits J. J Berzelisu at Stockholm, Sweden..
Class Metallic
Color Silvery White
Standard State Solid at 77 F & 298 K
Description Radioactive silvery metal. Metal protected by oxide coating. Attached by steam and slowly by acids. Metal itself is soft an ductile but alloys can be strong. Used in refractory materials, nuclear fuel elements, and incandescent gas mantles.

Diagnostic tests: 
Thorium is usually detected by radioactivity (due, in part, to the daughter elements such as radium). Uranium is also naturally radioactive; however, many uranium minerals are generally yellow or green and fluorescent, so if not, then suspect Th. Any radioactive mineral with a negative reaction to uranium tests is probably thorium.

Thorium is usually associated with the rare earth elements and use complicated schemes to identify the element. Basically, the rare earths and thorium are precipitated as hydroxides from acid solutions. The precipitate is dissolved in HCl and precipitated as insoluble oxalates, washed, filtered and ignited to the oxides. The oxide is dissolved in H2SO4 and ignited to dryness. Dissolve the sulphates in water and precipitate Th using boiling sodium thiosulfate solution.  Repeat the thiosulfate step if necessary to eliminate excess Ce, Zr, and Hf.

Infusible thorium minerals glow with exaggerated incandescence in the flame test (along with Sr, Mg, Zr, Zn, Ca - the "lime light effect").

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