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    Se

    Selenium

    Nonmetal

    Atomic Number: 34 • Atomic Mass: 78.9710 u • Period: 4 • Group: 16

    Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴
    Phase: Solid
    Electronegativity: 2.55
    Arsenic (As)Bromine (Br)
    OverviewPropertiesAtomic StructureOccurrenceApplicationsHistory

    Occurrence

    Selenium is found in various natural sources, including minerals, rocks, and the Earth's crust.

    • Relatively rare element, constituting about 0.000005% of Earth's crust
    • Rarely found in elemental form in nature
    • Often associated with sulfide ores of copper, zinc, and lead
    • Found in minerals such as crooksite and clausthalite
    • Present in some volcanic soils and waters