Selenium (Se)

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Selenium 34Se78.96

Discovered in 1817 by J.J. Berzelius at Stockholm, Sweden.

[Greek, selene = moon]

French: sélenium
German: Selen
Italian: selenio
Spanish: selenio

Description: Selenium is obtained in either a silvery metallic form (grey Se) or a red amorphous powder, which is less stable. Selenium burns in air, is unaffected by water, but dissolves in concentrated HNO3 and alkalis. It is used in photoelectric cells, photocopiers, solar cells and semiconductors.


Further Materials properties


Crystal structure:

(cell dimensions/pm), space group, 
grey hexagonal (a= 436.56, c=495.90) P3121, metallic form
α-Se monoclinic (a=906.4, b=907.2, c=115.6, β=90° 52'), P21/a, Se8
β-Se monoclinic (a=2851, b=807, c=931, β=93° 8'), P21/a, Se8
α'-Se cubic (a=297.0), Pm3m
β'-Se cubic (a=604), Fd3m

X-ray diffractions mass absorption coefficients: CuKa 91.4 (µ/r) / cm2g-1
MoKa 74.7 (µ/r) / cm2g-1
Neutron scattering length: 0.797 b/10-12 cm
Thermal neutron capture cross-section: 11.7 sa / barns
Density: 4790 (grey) kg/m-3 [293 K]; 3987 [liquid at m.p.]
Melting point: 216.85 °C / 490 °K
Boiling point: 684.95°C / 958.1°K
Molar volume: 16.48 cm3
Thermal conductivity: 2.04 (α) [300 K] W m-1K-1
Coefficient of linear thermal expansion: 36.9 x 10-6 K-1
Electrical resistivity: 0.01 [293 K] Ωm
Mass magnetic susceptibility: -4.0 x 10-9(s) kg-1m3
Radi: Se4+ 69Se2- 191; atomic 215; covalent 117: van der Waals 200
Electronegativity: 2.55 (Pauling); 2.48 (Allred); 5.89 eV (absolute)
Effective nuclear charge: 6.95 (Slater); 8.29 (Clementi); 9.96 (Froese-Fischer)
Number of Isotopes (incl. nuclear isomers): 26
Isotope mass range: 69 -> 89



Biological data


Biological role: Essential to some species, including humans, although only in tiny amounts. Selenium acts to stimulate the metabolism.
Toxic intake: human, Se metal = c. 10 - 35 mg
Lethal intake: LD50 (Se metal, oral, rat) = 6700 mg Kg-1. A dose of 5 mg per day can be lethal for many humans. LD50 (H2SeO3, intravenous, mouse) = 11 mg Kg-1
Hazards: Selenium compounds are toxic by inhalation and intravenous routes. They are also considered to be experimental carcinogens and teratogens.
Level in humans
Blood: 0.171 mg dm-3
Bone: 1 - 9 ppm
Liver: 0.35 - 2.4 ppm
Muscle: 0.42 - 1.9 ppm
Daily dietary intake: 0.006 - 0.2 mg 
Total mass of element in average
[70 kg] person:
c. 15 mg (wide range possible, 10-65 mg)


Geological data


Minerals:Native selenium is occasionally found; several minerals are known, but all are very rare and generally they occur together with sulfides of metals such as copper, zinc and lead.
MineralFormulaDensityHardnessCrystal apperance
Clausthalite  PbSe 7.8  2.5 - 3  cub., met. grey
Crooksite  Cu7TlSe4 6.9  2.5 - 3  tetragonal, met., grey

Note: the mineral called selenite is in fact calcium sulfate

Chief ores: by-product of electro-refining of copper.
World production: 1 600 tonnes/year
 Main mining areas: Canada, USA, Bolivia and Russia.
Reserves: n.a.
Specimen: available as powder or pellets. Care!


Sun: n.a. (relative to H = 1 x 1012)
Earth's crust: 0.05 ppm
Atlantic surface: 0.46 x 10-7 ppm
Atlantic deep: 1.8 x 10-7 ppm
Pacific surface: 0.15 x 10-7 ppm
Pacific deep: 1.65 x 10-7 ppm
Residence time: 3000 years
Classification: recycled
Oxidation state: VI (mainly) and IV

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

Other sizes and specifications on request

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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