Selenium презентация

Selenium

History Selenium (Greek σελήνη selene meaning "Moon") was discovered in 1817 by Jöns Jacob Berzelius, who noted the similarity of the new element to the previously discovered tellurium (named for the Earth).

Physical properties black, red, and gray (not pictured) allotropes Selenium salts are toxic in large amounts Nonmetal Hard

Chemical properties Se8 + 8 O2 → 8 SeO2 3 Se + 4 HNO3 + H2O → 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

Compounds H2SeO3selenous acid 2 SeO3 trioxide (K2SeO4) anhydrous potassium selenate    (Ag2SeO3) silver selenite     (Na2SeO3) sodium selenite  SeS2 Selenium disulfide H2SeO4 hydrogen peroxide (SeOCl2) selenium oxychloride 

Distribution in nature. Selenium is a rare and dispersed element; its content in the 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.

Uses In the vulcanization Catalyst in some chemical reactions Toning of photographic prints Se is used as a gamma source in industrial radiography

Medical use The substance loosely called selenium sulfide (approximate formula, SeS2) is the active ingredient 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.

In Kazakhstan We can find selenium and Tellurium in Altai, vicinity of the mountains Chingiz and Sayan, Konyrat,Shatyrkol , Zhezkazgan

By: Ratbek Yryszhan Bukharbayeva Makpal Kaldybekova Zilola Ramisova Ruzhdie Asan Tansholpan