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Selenium 34Se78.96
Discovered in 1817 by J.J. Berzelius at Stockholm, Sweden.
[Greek: selene = moon]
French: sélénium
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.
Materials properties
| Density: |
4790 (grey) kg/m-3 [293 K]; 3987 [liquid at m.p.] |
| Melting point: |
490 °K |
| Boiling point: |
958.1 °K |
| Critical temperature: |
1766 °K |
| Critical pressure: |
27200 °K |
| Molar volume: |
16.48 cm3 |
| Thermal conductivity: |
2.04 [300 K] Wm-1K-1 |
| Coefficient of linear thermal expansion: |
36.9 x 10-6 K-1 |
| Electrical resistivity: |
0.01 Wm |
| Mass magnetic susceptibility: |
-4.0 x 10-9(s) kg-1m3 |
| Young's modulus: |
58 GPa |
| Rigidity modulus: |
n.a. |
| Bulk modulus: |
n.a. |
| Poisson's ratio: |
0.447 GPa |
| Radii: |
Se4+ 69;Se2- 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 |
| Issotope 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. |
| Toxicity |
|
| Toxic intake: |
human, Se metal = c. 10 - 35 mg |
| Lethal intake: |
LD 50 (Se metal, oral, rat) = 6700 mg kg -1. A dose of 5 mg per day can be lethal for many humans. LD 50(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 p.p.m. |
| Liver: |
0.35 - 2.4 p.p.m. |
| Muscle: |
0.42 - 1.9 p.p.m. |
| 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) |
Crystal data
| Crystal structure, (cell dimentions / 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=1285, 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 diffraction: mass absorption coefficients (µ/ρ) /cm2g-1: |
CuKα 91.4 MoKα 74.7 |
| Neutron scattering length, b/10-12cm: |
0.797 |
| Thermal neutron capture cross-section, σa/barns: |
11.7 |
Geological data
| Minerals: |
Native selenium is occasionally found; several minerals are known, but all are very rare, and generally they occur together with sulfides or metals such as copper, zinc and lead. |
| Mineral |
Formula |
Density |
Hardness |
Crystal apperance |
| Clausthalite |
PbSe |
7.8 |
2.5 - 3 |
cub., met. grey |
| Crooksite |
Cu7TlSe4 |
6.90 |
2.5 - 3 |
tetragonal, met. grey |
| Chief ore: |
by-product of the electro-refining of copper. |
| World production: |
1600 tonnes/year |
| Main mining areas: |
Canada, USA, Bolivia, Russia |
| Reserves: |
n.a. |
| Specimen: |
available as powder or pellets. Care! |
| Abundances |
|
| Sun: |
n.a. |
| Earth's crust: |
0.05 p.p.m. |
| Seawater: |
|
| Atlantic surface: |
0.46 x 10-7 p.p.m. |
| Atlantic deep: |
1.8 x 10-7 p.p.m. |
| Pacific surface: |
0.15 x 10-7 p.p.m. |
| Pacific deep: |
1.65 x 10-7 p.p.m. |
| Residence time: |
3000 years |
| Classification: |
recycled |
| Oxidation state: |
VI (mainly) and IV |
Other sizes and specifications on request
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