Selenatom

Selenatom is the atom of the chemical element selenium (Se). Selenium is a nonmetal in group 16 (the chalcogens) of the periodic table, with atomic number 34 and period 4. A selenium atom has the electron configuration [Ar] 3d10 4s2 4p4. In standard state, selenium exists in several allotropes, most notably gray selenium, a semiconductor, and red selenium, which is more insulating. It commonly occurs in covalent compounds and as part of minerals; free selenium is rarely encountered.

Chemically, selenium forms a variety of compounds and oxidation states. The common oxidation states are -2, +4, and +6. It forms selenides (Se2−), selenites (SeO3 2−), and selenates (SeO4 2−), among others. As a semiconductor, gray selenium exhibits photoconductivity and has historically been used in rectifiers and photocopiers.

Occurrence and production: Selenium is found in nature primarily as a byproduct of the refining of copper, zinc, and other metal ores, often concentrated in sulfide minerals. It occurs in soils, sediments, and organic matter at trace levels. Commercial selenium is produced as a byproduct of ore processing and then refined to elemental selenium or compounds for industrial use.

Isotopes: Six stable isotopes exist for selenium: 74Se, 76Se, 77Se, 78Se, 80Se, and 82Se, with natural abundances of roughly 0.9%, 9–10%, 7–8%, 24–25%, 50%, and 9% respectively.

Biological role and safety: Selenium is an essential micronutrient for many organisms, incorporated into selenoproteins as the amino acid selenocysteine, which supports antioxidant defense and thyroid function. In humans, adequate intake is crucial, while deficiency can cause disease and impaired immune function; excess intake leads to selenosis. Toxicity can affect wildlife and humans at high environmental or occupational exposures.