Selenium

Selenium - Se

CAS: 7782-49-2
Description: Dark gray, lustrous rods or dark red, non-metallic crystals
Classification: Non-metal
Date of Discovery: 1817
Discoverer: Jons Berzelius
Name Origin: Greek Selênê, "moon"

Atomic Number: 34
Number of Neutrons: 45
Atomic Mass: 78.96(3) amu
Melting Point: 217 °C (gray)
Boiling Point: 685 °C (gray)
Density (293 K):
4.79 g/cm³ (gray)
4.28 g/cm³ (vitreous)
Atomic volume: 16.45 cm³/mol
Electrical resistivity: 1.0e^-12 10^-6/cm

Thermal conductivity: 0.0204 W/cmK
Enthalpy of atomization: 205.85 kJ/mol
Enthalpy of vaporization: 37.70 kJ/mol
Enthalpy of fusion: 6.694 kJ/mol
Specific heat capacity: 0.32 J/gK

Energy levels: 2-8-18-6
Electron configuration: [Ar]3d¹⁰4s²4p⁴
Crystal Structure: Hexagonal
Atomic radius: 1.22 Å
Covalent radius: 1.16 Å
Oxidation States: -2, +4, or +6
Electronegativity, Pauling: 2.55
Electron affinity: 2.020670 eV
First ionization energy: 9.752 eV
2nd ionization energy: 21.19 eV
3rd ionization energy: 30.82 eV
Polarizability: 3.77 10^-24cm³

Isotope	Natural Abundance	Atomic Mass	Half-life	Decay Mode	Spin
⁶⁵Se	64.965	0.011 s	⁺; ⁺, p
⁶⁷Se	66.9501	0.11 s	⁺
⁶⁸Se	67.9419	36 s	⁺
⁶⁹Se	68.93956	27.4 s	⁺; EC
⁷⁰Se	69.9335	41.1 m	⁺	0+
⁷¹Se	70.9319	4.7 m	⁺; EC	5/2-
⁷²Se	71.92711	8.5 d	EC	0+
^73mSe	40 m	IT; ⁺	3/2-
⁷³Se	72.92678	7.1 h	⁺; EC	9/2+
⁷⁴Se	0.89(2)	73.922477	Stable	0+
⁷⁵Se	74.922524	119.78 d	EC	5/2+
⁷⁶Se	9.36(11)	75.919214	Stable	0+
^77mSe	17.4 s	IT	7/2-
⁷⁷Se	7.63(6)	76.919915	Stable	1/2-
⁷⁸Se	23.78(9)	77.917310	Stable	0+
^79mSe	3.92 m	IT
⁷⁹Se	78.918500	6.5 x 10⁴ y	^-	7/2+
⁸⁰Se	49.61(10)	79.916522	Stable	0+
^81mSe	57.3 m	IT	7/2+
⁸¹Se	80.917993	18.5 m	^-	1/2-
⁸²Se	8.73(6)	81.916700	Stable	0+
^83mSe	1.17 m	^-	1/2-
⁸³Se	82.919119	22.3 m	^-	9/2+
⁸⁴Se	83.91847	3.3 m	^-	0+
⁸⁵Se	84.92225	32 s	^-	5/2+
⁸⁶Se	85.92428	15 s	^-	5/2-
⁸⁷Se	86.92853	5.4 s	^-
⁸⁸Se	87.93143	1.5 s	^-, n
⁸⁹Se	88.9360	0.41 s	^-, n
⁹¹Se	90.945	0.27 s	^-, n
Discovered by Berzelius in 1817, who found it associated with tellurium, named for the earth. Selenium is found in a few rare minerals such as crooksite [Cu₇(Tl,Ag)Se₄] and clausthalite (PbSe). In years past it has been obtained from flue dusts remaining from processing copper sulfide ores, but the anode metal from electrolytic copper refineries now provide the source of most of the world's selenium. Selenium is recovered by roasting the muds with soda or sulfuric acid, or by smelting them with soda and niter. Selenium exists in several allotropic forms. Three are generally recognized, but as many as that have been claimed. Selenium can be prepared with either an amorphous or crystalline structure. The color of amorphous selenium is either red, in powder form, or black, in vitreous form. Crystalline monoclinic selenium is a deep red; crystalline hexagonal selenium, the most stable variety, is a metallic gray. Naturally selenium contains six stable isotopes. Twenty-four other isotopes and isomers have been characterized. The element is a member of the sulfur family and resembles sulfur both in its various forms and in its compounds. Selenium exhibits both photovoltaic action, where light is converted directly into electricity, and photoconductive action, where the electrical resistance decreases with increased illumination. These properties make selenium useful in the production of photocells and exposure meters for photographic use, as well as solar cells. Selenium is also able to convert a.c. electricity to d.c., and is extensively used in rectifiers. Below its melting point selenium is a p-type semiconductor and is finding many uses in electronic and solid-state applications. It is used in Xerography for reproducing and copying documents, letters, etc. It is used by the glass industry to decolorize glass and to make ruby-colored glasses and enamels. It is also used as a photographic toner, and as an additive to stainless steel. Elemental selenium has been said to be practically nontoxic and is considered to be an essential trace element; however, hydrogen selenide and other selenium compounds are extremely toxic, and resemble arsenic in their physiological reactions. Hydrogen selenide in a concentration of 1.5 ppm is intolerable to man. Selenium occurs in some soils in amounts sufficient to produce serious effects on animals feeding on plants, such as locoweed, grown in such soils. LINKS: ATSDR - Public Health Statement: Selenium EcoIndiana: Selenium Is phytoremediation up to the selenium challenge? Minerals Containing Selenium Selenium and Cancer Prevention Selenium and Nutrition Selenium Forum Selenium Geochemistry Homepage Selenium Information Sheet Selenium in Diet Selenium Tellurium Development Association Return Sources for the information on this website include: Lide, David R., ed. CRC Handbook of Chemistry and Physics, 78th Ed., 1997-1998.

Site Navigation - want to skip?