thallium

Thallium is a chemical element with atomic number 81 and the symbol Tl. It was discovered independently by chemists William Crookes and Claude-Auguste Lamy in 1861, but Crookes was the first to publish and was the one to name the element. The name is from the Greek θαλλός (thallos, green plant shoot) + -ium, after the bright green line in the element’s spectrum.

Crookes published his discovery in March 1861, but the announcement did not propose a name. Two months later, he named it:

I have thought it best to give in the present article a few additional observations which I have since made, and also to propose for it, the provisional name of Thallium, from the Greek θαλλός, or Latin thallus, a budding twig,—a word which is frequently employed to express the beautiful green tint of young vegetation; and which I have chosen as the green line which it communicates to the spectrum recals [sic] with particular vividness the fresh colour of vegetation at the present time.

Thallium and its compounds are highly toxic. Thallium sulfate was once widely used as a pesticide, but this use is now generally banned out of safety concerns. Thallium salts were also used to treat various medical conditions, but these uses have largely been superseded by more effective and safer medicines. It is currently used in the manufacture of optical glass and of electronic components. A radioactive isotope is used in nuclear medicine, and the element may have practical applications in high-temperature superconductors.

Sources:

Crookes, William. “Further Remarks on the Supposed New Metalloid.” The Chemical News, 3.76, 18 May 1861, 303. HathiTrust Digital Archive.

———. “On the Existence of a New Element, Probably of the Sulphur Group.” The Chemical News, 3.69, 30 March 1861, 193–94. HathiTrust Digital Archive.

Miśkowiec, Pawel. “Name Game: The Naming History of the Chemical Elements: Part 2—Turbulent Nineteenth Century.” Foundations of Chemistry, 8 December 2022. DOI: 10.1007/s10698-022-09451-w.

Oxford English Dictionary, second edition, 1989, s.v. thallium, n.

Photo credit: Robert M. Lavinsky, before 2010. Wikimedia Commons. Licensed under a Creative Commons Attribution-Share Alike 3.0 Unported license.