Thallium - Information

Atomic Number: 81

Atomic Weight: 204.3833(2)

Electronic Configuration: [Rn]6s²5d¹⁰6p¹

Appearance - Thallium has a metallic lustre when it is not in contact with air. In air it develops a bluish-grey appearance similar to that of lead. It is very soft and malleable and can be cut with a knife.

Origin - From the Greek "thallos" a green twig or shoot. It was named when it gave a green spectral trail which identified the element.

History - Thallium was discovered in 1861 by William Crookes.

Sources - The major source of commercial thallium is the trace amounts found in copper, lead, zinc, and other sulfide ores. Manganese nodules from the ocean floor are known to contain thallium. It is more commonly found in a few ores such as crooksite and hutchinsonite. It is recovered by roasting the ore with the production of sulphuric acid.

Uses -

• It is known that up to 25 isotopes of thallium exist.
• Thallium is an effective rodenticide and ant killer although it is banned in some countries.
• Its electrical conductivity changes with exposure to infra-red light so is used in photo cells.
• Thallium bromide-iodide crystals could be used as infrared optical materials.
• Thallium has been used in treating ringworm and other skin infections but its use is limited as it is quite toxic.