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A bluish-gray metallic element. Thallium was first identified by William Crookes in 1861. It has an abundance of about 0.7 ppm in the earth's crust and occurs mainly in the minerals crookesite, lorandite and hutchinsonite. Thallium is recovered as a byproduct of lead and zinc smelting. The soft metal can be cut with a knife. Thallium tarnishes on exposure to air forming highly toxic oxides, carbonates and hydroxides. Metallic thallium has been used in the manufacture of photocells, infrared detectors, low-melting point glasses and low-temperature thermometers, relays and switches. Thallium salts have been used in to make artificial diamonds, green pyrotechnics as well as for ant and rodent poisons.

Synonyms and Related Terms

Tl; ramor

Other Properties

Soluble in nitric and sulfuric acids. Insoluble in water, but reacts with air and water to become soluble. Flame color is greenish blue.

Composition Tl (atomic no. 81)
CAS 7440-28-0
Melting Point 302-303
Density 11.85
Molecular Weight atomic wt. = 204.37
Boiling Point 1457

Hazards and Safety

Forms toxic compounds on contact with moisture. Can be absorbed through the skin. Reacts violently with halogens. Hazardous to the environment.

LINK: International Chemical Safety Card