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For insecticides. | Atomic Number: | 81 | Atomic Symbol: | Tl | | Atomic Weight: | 204.37 | Electron Configuration: | 2-8-18--32-18-3 | | Shells: | 2,8,18,32,18,3 | Filling Orbital: | 6p1 | | Melting Point: | 303.5oC | Boiling Point: | 1457oC | | Description: | Soft bluish gray metal that looks like lead. |
| Uses: | Its compounds are used in rat and ant poisons.
Also used for
detecting infrared radiation. |
History(Gr. thallos, a green shoot or twig) Thallium was discovered
spectroscopically in 1861 by Crookes. the element was named after the beautiful
green spectral line, which identified the element. The metal was isolated both
by Crookes and Lamy in 1862 about the same time. Thallium occurs in crooksite,
lorandite, and hutchinsonite. It is also present in pyrites and is recovered
from the roasting of this ore in connection iwth the production of sulfuric
acid. It is also obtained from the smelting of lead and zinc ores. Extraction is
somewhat complex and depends on the source of the thallium. Manganese nodules,
found on the ocean floor, contain thallium. When freshly exposed to air,
thallium exhibits a metallic luster, but soon develops a bluish-gray tinge,
resembling lead in appearance. A heavy oxide builds up on thallium if left in
air, and in the presence of water the hydride is formed. The metal is very soft
and malleable. It can be cut with a knife. Twenty five isotopic forms of
thallium, with atomic masses ranging from 184 to 210 are recognized. Natural
thallium is a mixture of two isotopes. The element and its compounds are toxic
and should be handled carefully. Contact of the metal with skin is dangerous,
and when melting the metal adequate ventilation should be provided. Exposure to
thallium (soluble compounds) - skin, as Tl, should not exceed 0.1 mg/m^3 (8-hour
time-weighted average - 40-hour work week). Thallium is suspectied of
carcinogenic potential for man. Thallium sulfate has been widely employed as a
rodenticide and ant killer. It is odorless and tasteless, giving no warning of
its presence. Its use, however, has been prohibited in the U.S. since 1975 as a
household insecticide and rodenticide. The electrical conductivity of thallium
sulfide changes with exposure to infrared light, and this compound is used in
photocells. Thallium bromide-iodide crystals have been used as infrared optical
meterials. Thallium has been used, with sulfur or slenium and arsenic, to
produce low melting glasses with become fluid between 125 and 150C. These
glasses have properties at room temperatures similar to ordinary glasses and are
said to be durable and insoluble in water. Thallium oxide has been used to
produce glasses with a high index of refraction. Thallium has been used in
treating ringworm and other skin infections; however, its use has been limited
because of the narrow margin between toxicity and therapeutic benefits. A
mercury-thallium alloy, which forms a eutectic at 8.5% thallium, is reported to
freeze at -60C, some 20 degrees below the freezing point of mercury. Commercial
thallium metal (99%) costs about $40/lb.
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