Thallium

Symbol: TI
Date of discovery: 1861
Name origin: Greek thallos
Appearance: silvery white
Discoverer: Sir William Crookes
Obtained from: copper, lead, zinc, sulfide ores

Melting point: 303.5 K
Boiling point: 1473 K
Density[kg/m³]: 11.85
Molar volume: 17.22×10^-6 m³/mol
Protons/Electrons: 81
Neutrons: 123
Shell structure: 2,8,18,32,18,3
Electron configuration: Xe 4f14 5d10 6s2 6p1
Oxidation state: 3,1
Crystal structure: Hexagonal

Thallium was discovered spectroscopically in 1861 by Sir William Crookes. Very soft and malleable, thallium can be cut with a knife at room temperature. This element exhibits a metallic luster when freshly exposed to air, but soon becomes bluish-grey, resembling tin or lead. The element and its compounds are toxic and must be handled carefully. Thallium is believed to cause cancer. Thallium-doped silicon is a semiconductor material used in infrared detectors. Thallium bromide-iodide crystals may also be found in infrared detectors. Thallium is used as a rat and ant killer. It was originally used in treating ringworm and other skin infections.