Thallium, Physical and Chemical Properties

Thallium is a silvery white metal, considered a less typical metal because when it loses its outermost electrons it will not achieve the inert gas electronic structure. It occurs as a trace element in pyrite, and is extracted as a by-product of roasting this mineral for the production of sulfuric acid. Thallium can also be obtained from the smelting of lead and zinc sulfide ores. The fresh surface of the metal has a bluish-white luster. In many of its physical properties, thallium resembles its neighbor, lead. It exists in two allotropic forms: α-thallium, hexagonal close-packed, stable at room temperature; and β-thallium, body-centered cubic, stable above 226°C. A volume increase of 3.23% takes place on solidification.

Thallium and its compounds are extremely toxic. The odorless and tasteless thallium sulfate was once widely used as rat poison and ant killer. Thallium (I) sulfide’s electrical conductivity changes with exposure to infrared light therefore making this compound useful in...