Thallium (Tl)

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Thallium 81Tl204.3833

Thallium was discovered in 1861 by William Crookes at London, England. Isolated in 1862 by C. A. Lamy at Paris, France.

[Greek, thallos = green twig]

French: thallium
German: Thallium
Italian: tallio
Spanish: talio

Description: Thallium is a soft, silvery-white metal, which tarnishes readily in moist air and reacts with steam to form TlOH. It is attacked by acids, rapidly so by HNI3. Thallium is little used because of its toxicity, but is still employed in special types of glass. 

Further Materials properties


Crystal structure:

(cell dimensions/pm), space group, 
α-Tl heaxagonal (a=345.6, c=552.6) P63/mmc
β-Tl cubic (a=388.2), Im3m
γ-Tl f.c.c. (a=485.1), Fm3m
T (α -> β) = 503 K

X-ray diffractions mass absorption coefficients: CuKa 224 (µ/r) / cm2g-1
MoKa 119 (µ/r) / cm2g-1
Neutron scattering length: 0.8776 b/10-12 cm
Thermal neutron capture cross-section: 3.43 sa / barns
Density: 11 850 kg/m-3 [293 K]
Melting point: 303.55°C / 576.7°K
Boiling point: 1456.85°C / 1730°K
Molar volume: 17.24 cm3
Thermal conductivity: 46.1 [300 K] W m-1K-1
Coefficient of linear thermal expansion: 28 x 10-6 K-1
Electrical resistivity: 18 x 10-8 [295 K] Ωm
Mass magnetic susceptibility: -3.13 x 10-9(s) kg-1m3
Radi: Tl3+ 105Tl+ 149; atomic 170; covalent 155
Electronegativity: 1.62 (TlI) 2.04 (TlIII) (Pauling); 1.44 (Allred); 3.2 eV (absolute)
Effective nuclear charge: 5.00 (Slater); 12.25 (Clementi); 13.50 (Froese-Fischer)
Number of Isotopes (incl. nuclear isomers): 41
Isotope mass range: 184 -> 210



Biological data


Biological role: None.
Toxic intake: metal, oral, human = 5.7 mg Kg-1
Lethal intake: ingestion of 0.2 - 1g Tl2SO4 for humans. LD50 (Tl2SO4, oral, mouse) = 29 mg Kg-1
Hazards: Thalium compounds are extremely toxic and cumulative; they are also absorbed through the skin. Thallium takes several days to act and affects the nervous system. It is also teratogenic.
Level in humans
Blood: 0.00048 mg dm-3
Bone: 0.002 ppm
Liver: 0.004 - 0.033 ppm
Muscle: 0.07 ppm
Daily dietary intake: 0.0015 mg
Total mass of element in average
[70 kg] person:

0.5 mg

Geological data


Minerals:Thallium minerals are rare, but the element is dispersed in potassium minerals such as sylvite and the caesium mineral pollucite.
MineralFormulaDensityHardnessCrystal apperance
Crookesite  Cu7TlSe4 6.9  2.5 - 3 tet., metallic grey
Hutchinsonite (Tl,Pb)2As5S9 4.6  1.5 - 2 orth., adam. red
Lorandite TlAsS2 5.53  2 - 2.5 mon., met. adamantine red/grey
Thalcusite Cu3FeTl2S4 6.54  2.5 tet., metallic grey

Chief ores:  thallium is generally obtained as the by-product of zinc and lead smelting.
World production:  30 tonnes/year
Main mining areas:  see zinc and lead
Reserves:  n/a
Specimen:  available as granules. Danger!


Sun: 8.0 (relative to H = 1 x 1012)
Earth's crust: 0.6 ppm
Seawater 1.4 x 10-5
Residence time: 10 000 years
Classification: accumulating
Oxidation state: I

  Source: Emsley, J. (1998) The Elements (3rd Edition)

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Overview of elements with access to our shop

1 18
2 13 14 15 16 17
Li Be B C
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se
Rb Sr Y Zr Nb Mo
Ru Rh Pd Ag Cd In Sn Sb Te I
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi
Ce Pr Nd
Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

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