Se
SELENIUM
(Gr. Selene, moon)
Se at. wt. 78.96
at. no. 34
m.p. 217°C (gray)
b.p. 684.9&plusm;1.0°C (gray)
sp. gr. 4.79 (gray)
sp. gr. 4.28 (vitreous)
valence - 2, +4, or +6.
Electronic configuration
| SHELL |
K |
L |
M |
N |
O |
P |
Q |
| SUB SHELL |
He |
Neon |
Argon |
Krypton |
Xenon |
Radon |
Eka-radon |
| 1s |
2s 2p |
3s 3p |
3d 4s 4p |
4d 5s 5p |
4f 5d 6s 6p |
5f 6d 7s 7p |
| Selenium
|
1s22s22p63s23p63d104s24p4 |
|
|
|
| Symbol
|
3P2 |
Selenium was discovered by Berzelius'in 1817, who found it associated
with tellurium, named for the earth. Selenium is found in a
few rare minerals, s'uch as crooksite and clausthalite. In
years !%ast it has been obtained from flue dusts remaining
from' processing copper sulfide ores, but the anode muds
from electrolytic copper refineries now provide tht 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 allo-
tropic forms. Three are generally recognized, but as many
as six have been claimed. Selenium can be prepared with
either' an amorphous or crystalline structure. The color of
amorphous selenium is either red, in powder fonrr, or black,
in vitreous form. Crystalline monoclinic selenium is 'a deep
red; crystalline hexagonal selenium, the most stable variety,
is a metallic gray. Natural selenium contains six stable iso-
topes. Fourteen other nuclides 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 electric' Ity, and p'hot~
conductive action, where the electrical resistance decreases
with increased,iltumination. These properties make selenium
useful in the production of photo~ells 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 re-
producing 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; however,
hydrogen selenide and other~ selenium compounds are
extremely toxic, and resemble arsenic in its 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.
The maximum allowable concentration of selenium com-
pounds in air has been recommended to be 0.1 mg/cu meter.
Selenium is priced at about $5/lb. It is also available in hig'h-
purity form at a somewhat higher cost.
© 1999 F. Davies
Delphi O.E.M. Co.
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