Selenium

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Selenium is a chemical element in the periodic table that has the symbol Se and atomic number 34.

Properties

General
Name, Symbol, Number	Selenium, Se, 34
Series	Nonmetals
Group, Period, Block	16(VI), 4 , p
Density, Hardness	4790 kg/m3(300K), 2
Appearance	grey, metallic lustre
Atomic
Atomic weight	78.96 amu
Atomic radius (calc.)	115 (103)pm
Covalent radius	116 pm
van der Waals radius	190 pm
Electron configuration	[Ar]3d104p44s2
e- 's per energy level	2, 8, 18, 6
Oxidation states (Oxide)	±2,4,6 (strong acid)
Crystal structure	hexagonal
Physical
State of matter	solid (__)
Melting point	490 K (__ °F)
Boiling point	957.8 K (__ °F)
Molar volume	__ ×10-3 m3/mol
Heat of vaporization	__ kJ/mol
Heat of fusion	__ kJ/mol
Vapor pressure	__ Pa at __ K
Velocity of sound	__ m/s at __ K
Miscellaneous
Electronegativity	2.48 (Pauling scale)
Specific heat capacity	__ J/(kg*K)
Electrical conductivity	__ 106/m ohm
Thermal conductivity	__ W/(m*K)
1st ionization potential	__ kJ/mol
2nd ionization potential	__ kJ/mol
3rd ionization potential	__ kJ/mol
4th ionization potential	__ kJ/mol
Most Stable Isotopes
iso NA half-life DM DE MeV DP ___ {syn.} __ __ __ [[__|___]] 74Se 0.87% Se is stable with 40 neutrons 76Se 9.0% Se is stable with 42 neutrons 77Se 7.5% Se is stable with 43 neutrons 78Se 23.5% Se is stable with 44 neutrons 80Se 49.8% Se is stable with 46 neutrons 82Se 9.1% __ is stable with 48 neutrons ___ trace __ __ __ [[__|___]]
SI units & STP are used except where noted.

Notable Characteristics

Selenium exists in a number of allotropic forms. In the powdered form, amorphous selenium is red, while the vitreous form is black. Crystalline hexagonal selenium is a metallic grey, while the monoclinic crystal is a deep red color.

Selenium exhibits a photovoltaic effect, converting light to electricity, and a photoconductive effect, electrical conductance increasing as selenium is exposed to light. Below its melting point, selenium is a p type semiconductor.

Uses

Selenium is an essential micronutrient in all known forms of life; it is a component of the unusual amino acid selenocysteine. Because of its photovoltaic and photoconductive properties, selenium is used extensively in electronics, such as photo cells, and solar cells. Selenium is also extensively used in rectifiers.

Selenium is used to remove color from glass, as it will counteract the green color ferrous impurities impart. It also can be used to give a red color to glasses and enamels. Selenium is used to improve the abrasion resistance in vulcanized rubbers. It also finds application in photocopying.

Another use for selenium is the toning of photographs, and is sold by numerous photographic manufacturers including Kodak and Fotospeed. Its artistic use is to intensify and extend the tonal range of black and white photographic images, and it can also be used for increasing the permanence of images.

History

Selenium is derived from "selene," the latin word for the Moon. Selenium was discovered in 1817 by Jons Jacob Berzelius,

Sources

Selenium occurs as selenide in many sulfide ores, such as those of copper, silver, or lead. It is obtained as a byproduct of the processing of these ores, from the anode mud of copper refineries and the mud from the lead chambers of sulfuric acid plants. These muds can be processed by a number of means to obtain free selenium.

Precautions

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Information sources and external links:

Los Alamos National Laboratory - Selenium
WebElements.com - Selenium
EnvironmentalChemistry.com - Selenium