Selenium

noted the similarity of the new element to the previously discovered tellurium (named for the Earth).

History

large amounts
Nonmetal
Hard

Physical properties

3 H2SeO3 + 4 NO
2 SeO3 → 2 SeO2 + O2 (ΔH = −54 kJ/mol)
H2SeO3 + 2 H2S → SeS2 + 3 H2O
SeO2 + H2O2 → H2SeO4
Se8 + 24 F2 → 8 SeF6
Al2Se3 + 6 H2O → Al2O3 + 6 H2S
8 KCN + Se8 → 8 KSeCN

Chemical properties

peroxide
(SeOCl2) selenium oxychloride 

Compounds

earth’s crust (clarke) is 5 X 10–6 percent by weight. The history of selenium in the earth’s crust is closely linked to that of sulfur. Selenium displays a tendency toward concentration and, despite its low clarke, forms 38 minerals of its own, including selenides, selenites, and selenates. Isomor-phous admixtures of selenium are characteristic in sulfides and native sulfur.
Selenium undergoes active migration in the biosphere. Igneous rocks, volcanic gases, and volcanic hot springs are sources of selenium accumulations in organisms. For this reason, the soils and sedimentary rocks in active and dormant volcanic regions are often enriched with selenium. Here, the average content in clays and shales is 6 × 10–5 percent.

Distribution in nature.

is used as a gamma source in industrial radiography

Uses

in some anti-dandruff shampoos. The selenium compound kills the scalp fungus Malassezia, which causes shedding of dry skin fragments. The ingredient is also used in body lotions to treat tinea versicolor due to infection by a different species of Malassezia fungus.

Medical use

mountains Chingiz and Sayan, Konyrat,Shatyrkol , Zhezkazgan

In Kazakhstan