Thallium: the essentials

When freshly exposed to air, thallium exhibits a metallic lustre, but soon develops a bluish-grey tinge, resembling lead in appearance. A heavy oxide builds up on thallium if left in air, and in the presence of water the hydroxide is formed. The metal is very soft and malleable. It can be cut with a knife.

The element and its compounds are toxic and should be handled carefully. Thallium may cause cancer.

Table: basic information about and classifications of thallium.

Thallium: historical information

Thallium was discovered by Sir William Crookes at 1861 in England. Origin of name: from the Greek word "thallos" meaning "green twig" or green shoot.

Thallium was discovered spectroscopically in 1861 by Crookes. The element was named after the green spectral line, which identified the element (Greek "thallos", green twig). The metal was isolated both by Crookes and Lamy in 1862. They had been expecting to isolate tellurium after removing selenium from the byproducts from a commercial sulphuric acid factory but instead foundthe new element thallium.

Thallium: physical properties

 Read more » »

Thallium: orbital properties

 Read more » »


Isolation: thallium metal would not normally be made in the laboratory as it is available commercially. Crude thallium is present as a component in flue dust along with arsenic, cadmium, indium, germanium, lead, nickel, selenium, tellurium, and zinc. This is done by dissolving in dilute acid, precipitating out lead sulphate, and then adding HCl to precipitate thallium chloride, TlCl. Further purification can be achieve by electrolysis of soluble thallium salts.

WebElements Shop

WebElements now has a WebElements shop at which you can buy periodic table posters, mugs, T-shirts, games, fridge magnets, molecular models, and more.

Periodic Table fridge magnets Periodic Table fridge magnets
Buy our periodic table fridge magnets here

WebElements poster Periodic table t-shirts Periodic table mouse mats Molymod molecular model kits Chemistry educational resources

thallium atomic number