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.


Science and Ink cartoon for thallium
Cartoon by Nick D Kim ([Science and Ink], used by permission).

Thallium: historical information

Thallium was discovered by Sir William Crookes in 1861 at 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 around us Read more »

Thallium has no biological role. Thallium compounds are extremely toxic. Their effects are cumulative and they can be absorbed though the skin. Thallium poisoning takes several days to act and it affects the nervous system.

Thallium minerals are rare but include crooksite, lorandite, pyrites, and hutchinsonite. Thallium is also associated with potassium minerals such as sylvite and mineral pollucite. Thallium is also produced as a byproduct from zinc and lead refining plants, as well as from particular sulphuric acid factories.

Abundances for thallium in a number of different environments. More abundance data »
Location ppb by weight ppb by atoms Links
Universe 0.5 0.003 Chemical elements abundance by weight in the universe on a miniature periodic table spark table
Crustal rocks 530 50 Chemical elements abundance by weight in the earth's crust on a miniature periodic table spark table
Human (no data) ppb by weight (no data) atoms relative to C = 1000000 Chemical elements abundance by weight in humans on a miniature periodic table spark table

Physical properties Read more »

Heat properties Read more »

Crystal structure Read more »

The solid state structure of thallium is: hcp (hexagonal close-packed).

Thallium: orbital properties Read more »

Thallium atoms have 81 electrons and the shell structure is The ground state electronic configuration of neutral Thallium is [Xe].4f14.5d10.6s2.6p1 and the term symbol of Thallium is 2P1/2.


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.

Thallium isotopes Read more »

Thallium has two stable isotopes and one of these, Tl-203, is used to produce one of the (workhorses( of nuclear medicine: Tl-201. Tl-201 is used extensively for imaging and in particular for perfusion tests of the myocardium. These tests are done to determine the damage to the heart from a heart attack or from heart diseases. Tl205 has been proposed as an alternative target for the production of Tl-201. Tl-205 is also used in nuclear magnetic resonance research.

Table. Stables isotopes of thallium.
Isotope Mass
(atom %)
spin (I)
moment (μ/μN)
203Tl 202.972320 (5) 29.524 (14) 1/2 1.622257
205Tl 204.974401 (5) 70.476 (14) 1/2 1.6382135

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