thallium

[thal-ee-uhm]
noun Chemistry.
a soft, malleable, rare, bluish-white metallic element: used in the manufacture of alloys and, in the form of its salts, in rodenticides. Symbol: Tl; atomic weight: 204.37; atomic number: 81; specific gravity: 11.85 at 20°C.

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

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World English Dictionary
thallium (ˈθælɪəm)
 
n
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
 
[C19: from New Latin, from Greek thallos a green shoot; referring to the green line in its spectrum]

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Etymonline
Word Origin & History

thallium
rare metallic element, 1861, Mod.L., from Gk. thallos "young shoot, green branch," so called by its discoverer, Sir William Crookes (1832-1919), from the green line in its spectrum. Gk. thallos is related to thalia "abundance," thalos "scion, child," ult. from PIE base *dhal- "to bloom" (cf. O.Ir. duilesc,
a type of algae).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

thallium thal·li·um (thāl'ē-əm)
n.
Symbol Tl
A soft, malleable, highly toxic metallic element, used in photocells, infrared detectors, and low-melting glass. Atomic number 81; atomic weight 204.38; melting point 303.5°C; boiling point 1,473°C; specific gravity 11.85; valence 1, 3.

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American Heritage
Science Dictionary
thallium   (thāl'ē-əm)  Pronunciation Key 
Symbol Tl
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. See Periodic Table.
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Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica
Encyclopedia

thallium

(Tl), chemical element, metal of main Group IIIa, or boron group, of the periodic table, poisonous and of limited commercial value. Like lead, thallium is a soft, low-melting element of low tensile strength. Freshly cut thallium has a metallic lustre that dulls to bluish gray upon exposure to air. The metal continues to oxidize upon prolonged contact with air, generating a heavy nonprotective oxide crust. Thallium dissolves slowly in hydrochloric acid and dilute sulfuric acid and rapidly in nitric acid.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
Statistics and information on the worldwide supply, demand, and flow of thallium.
Small amounts of thallium are used to make certain medical agents and electronics.
Exposure to higher levels of thallium may occur in the workplace.
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