thallium

American  

[thal-ee-uhm] / ˈθæl i əm /

noun

Chemistry.

1. a soft, malleable, rare, bluish-white metallic element: used in the manufacture of alloys and, in the form of its salts, in rodenticides. Tl; 204.37; 81; 11.85 at 20°C.

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thallium British  

/ ˈθælɪəm /

noun

1. a soft malleable highly toxic white metallic element used as a rodent and insect poison and in low-melting glass. Its compounds are used as infrared detectors and in photoelectric cells. Symbol: Tl; atomic no: 81; atomic wt: 204.3833; valency: 1 or 3; relative density: 11.85; melting pt: 304°C; boiling pt: 1473±10°C

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thallium Scientific  

/ thăl′ē-əm /

1. A soft, malleable, very poisonous metallic element that is used in photography, in making low-melting and highly refractive glass, and in treating skin infections. Atomic number 81; atomic weight 204.38; melting point 303.5°C; boiling point 1,457°C; specific gravity 11.85; valence 1, 3.

2. See Periodic Table

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Etymology

Origin of thallium

1860–65; < New Latin, equivalent to thall- (< Greek thallós green stalk) + -ium -ium; named after green line in its spectrum

Example Sentences

The 8th century Katla eruption created a 12-year spike in metals like bismuth and thallium in Greenland ice cores.

From Science Daily • Mar. 20, 2026

Much of the thallium in the Baltic Sea, the largest human-induced hypoxic area on Earth, accumulates in the sediment thanks to abundant sulfide minerals.

From Science Daily • May 2, 2024

Reports have claimed Ms Sun had access to the thallium compound but she has said she was not the only student with access to the toxic substance.

From BBC • Dec. 23, 2023

Lepidolite extraction and smelting produces toxic by-products like thallium and tantalum that cause severe water pollution, said Wu Wei, an assistant professor at Xiamen University.

From Reuters • Jun. 15, 2023

He has frequently found it, he says, in the dark-coloured varieties, and considers the variations of colour in cadmium sulphide to be owing to traces of thallium.

From Field's Chromatography or Treatise on Colours and Pigments as Used by Artists by Salter, Thomas