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Thallium [Tl] locate me
CAS-ID: 7440-28-0
An: 81 N: 123
Am: 204.3833 g/mol
Group No: 13
Group Name: Metals
Block: p-block  Period: 6
State: solid at 298 K
Colour: silvery white Classification: Metallic
Boiling Point: 1746K (1473°C)
Melting Point: 577K (304°C)
Superconducting temperature: 2.38K (-270.77°C)
Density: 11.85g/cm3
Discovery Information
Who: Sir William Crookes
When: 1861
Where: England
Name Origin
Greek: thallos (young shoot) from a bright-green line in its spectrum.
 "Thallium" in different languages.
Sources
Found in iron pyrites. Also in the minerals crookesite (TlCu7Se4), hutchinsonite (TlPbAs5S9) and lorandite (TlAsS2). It is found in the Earth's crust at a concentration estimated to be 0.6mg/kg. Annual production is around 30 tons.
Abundance
 Universe: 0.0005 ppm (by weight)
 Sun: 0.001 ppm (by weight)
 Carbonaceous meteorite: 0.08 ppm
 Earth's Crust: 0.6 ppm
 Seawater: 1.4 x 10-5 ppm
Uses
Its compounds were used in rat and ant poisons, but this use is no longer allowed in many countries due to safety concerns. Also for in gamma radiation detecting equipment, detecting infrared radiation and heart muscle research. Thallium sulfide's electrical conductivity changes with exposure to infrared light therefore making this compound useful in photocells.
Combined with sulfur or selenium and arsenic, thallium has been used in the production of high-density glasses that have low melting points in the range of 125 and 150°C. These glasses have room temperature properties that are similar to ordinary glasses and are durable, insoluble in water and have unique refractive indices.
Thallium amalgam is used in thermometers for low temperature, because it freezes at -58°C (pure mercury freezes at -38°C).
History
Thallium was discovered by Sir William Crookes in 1861 in England while he was making spectroscopic determinations for tellurium on residues from a sulfuric acid plant. The name comes from Thallium's bright green spectral emission lines. In 1862 Crookes and Claude-Auguste Lamy isolated the metal independently of each other.
Notes
This metal is very soft and malleable and can be cut with a knife. When it is first exposed to air, thallium has a metallic luster but quickly tarnishes with a bluish-gray tinge that resembles lead (it is preserved by keeping it under oil). A heavy layer of oxide builds up on thallium if left in air. In the presence of water, thallium hydroxide is formed.
Hazards
Thallium and its compounds are highly toxic and should be handled with great care. Thallium is a suspected human carcinogen.
Thallium was once an effective murder weapon before its effects became understood and an antidote (prussian blue) discovered.