34 78.971
Se
Selenium

Selenium , Se

Selenium is a chemical element with atomic number 34, with the chemical symbol Se. It is a nonmetal, chemically related to sulfur and tellurium, and rarely occurring in its elemental state in nature. It is toxic in large amounts, but trace amounts of it are necessary for cellular function in most, if not all, animals, forming the active center of the enzymes glutathione peroxidase and thioredoxin reductase (which indirectly reduce certain oxidized molecules in animals and some plants) and three known deiodinase enzymes (which convert one thyroid hormone to another). Selenium requirements in plants differ by species, with some plants apparently requiring none.

 

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S3-5001-M

Se 1-3mm shot 99.999% Pure

Selenium

6.1 UN3288 PG III Toxic

S3-5002-M

Se 1-6mm Pieces 99.999% Pure

Selenium

6.1 UN3288 PG III Toxic

S3-5005-M

SeOCl2 Liquid (MP8.5oC BP176.4oC) 99.9% Pure

Selenium Oxychloride

UN2879 8, (6.1) PG I

S3-10004-P

SeCl -8 mesh 99.8% Pure

Selenium Chloride

8 UN2922 PG II Toxic

S3-10005-P

SeO2 -20 mesh 99.999% Pure

Selenium Oxide

UN3283 PG II Toxic

S3-10006-P

SeO2 -20 mesh 99.5% Pure

Selenium Oxide

UN3283 PG II Toxic

S3-10007-P

SeOBr2 -8 mesh 99.5% Pure

Selenium Oxybromide

8 UN2923 PG I Corrosive/Toxic

S3-2000-R

Se Rod 20mm dia. x 6mm long 99.9% Pure

Selenium

S3-9000-D

Selenium Se,

Purity 99.9%, 99.99% & 99.999%

S3-9001-D

Selenium-Arsenide-Germanium Se-As-Ge,

Available in various ratios wt% or at%, Purity 99.9%

S3-9002-D

Selenium-Arsenide-Silicon-Germanium Se-As-Si-Ge,

Available in various ratios wt% or at%, Purity 99.9%

SE-ST-1-3-5N

Se TRG 25.4mm dia. x 3.18mm Tk 99.999% Pure

Selenium

SE-ST-1-6-5N

Se TRG 25.4mm dia. x 6.35mm Tk 99.999% Pure

Selenium

SE-ST-2-3-4N

Se TRG 50.8mm dia. x 3mm Tk 99.99% Pure

Selenium

SE-ST-2-3-5N

Se TRG 50.8mm dia. x 3mm Tk 99.999% Pure

Selenium

SE-ST-2-6-4N

Se TRG 50.8mm dia. x 6.35mm Tk 99.99% Pure

Selenium

SE-ST-3-3-4N

Se TRG 76.2mm dia. x 3mm Tk 99.99% Pure

Selenium

Isolated selenium occurs in several different forms, the most stable of which is a dense purplish-gray semimetal (semiconductor) form that is structurally a trigonal polymer chain. It conducts electricity better in the light than in the dark, and is used in photocells (see allotropic section below). Selenium also exists in many nonconductive forms: a black glass-like allotrope, as well as several red crystalline forms built of eight-membered ring molecules, like its lighter chemical cousin sulfur.

Selenium is found in economic quantities in sulfide ores such as pyrite, partially replacing the sulfur in the ore matrix. Minerals that are selenide or selenate compounds are also known, but all are rare.

Symbol Se
Atomic number 34
No. of naturally occurring isotopes 6
Atomic weight 78.96(+/-0.03)
Electronic configuration [Ar]3dl04s24p4
Atomic radius(12-coordinate)/pm 140*
Ionic radius(6-coordinate)/pm M2- 198
Ionic radius(6-coordinate)/pm M4+ 50
Ionic radius(6-coordinate)/pm M6+ 42
Electronegativity χ 2.4
Density (25°C)/gcm-3 (Hexagonal) 4.189
Density (25°C)/gcm-3 (Monoclinic) 4.389
Density (25°C)/gcm-3 (Vitreous) 4.285
Melting point / °C 217
Boiling point / °C 685
ΔHatomization/kJmol-1 206.7
Ionization energy/kJmol-1 940.7
Band gap Eg/kJmol-1 178
Electrical resistivity (25°C)/μohm cm 1010**
Temperature (oC) @Vap. Pressure
10-8 Torr 89
10-6 Torr 125
10-4 Torr 170
Techniques
Electron Beam Good
Crucible Al2O3 & Vitreous Graphite
Coil Tungsten & Molybdenum
Boat Tungsten & Molybdenum
Remarks
Toxic. Poisons vacuum systems.