Selenium

  • selenium, 34se
    seblackred.jpg
    selenium
    pronunciationm/ (lee-nee-əm)
    appearanceblack, red, and gray (not pictured) allotropes
    standard atomic weight ar, std(se)78.971(8)[1]
    selenium in the periodic table
    hydrogen helium
    lithium beryllium boron carbon nitrogen oxygen fluorine neon
    sodium magnesium aluminium silicon phosphorus sulfur chlorine argon
    potassium calcium scandium titanium vanadium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton
    rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine xenon
    caesium barium lanthanum cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium holmium erbium thulium ytterbium lutetium hafnium tantalum tungsten rhenium osmium iridium platinum gold mercury (element) thallium lead bismuth polonium astatine radon
    francium radium actinium thorium protactinium uranium neptunium plutonium americium curium berkelium californium einsteinium fermium mendelevium nobelium lawrencium rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium roentgenium copernicium nihonium flerovium moscovium livermorium tennessine oganesson
    s

    se

    te
    arsenicseleniumbromine
    atomic number (z)34
    groupgroup 16 (chalcogens)
    periodperiod 4
    blockp-block
    element category  reactive nonmetal, sometimes considered a metalloid
    electron configuration[ar] 3d10 4s2 4p4
    electrons per shell2, 8, 18, 6
    physical properties
    phase at stpsolid
    melting point494 k ​(221 °c, ​430 °f)
    boiling point958 k ​(685 °c, ​1265 °f)
    density (near r.t.)gray: 4.81 g/cm3
    alpha: 4.39 g/cm3
    vitreous: 4.28 g/cm3
    when liquid (at m.p.)3.99 g/cm3
    critical point1766 k, 27.2 mpa
    heat of fusiongray: 6.69 kj/mol
    heat of vaporization95.48 kj/mol
    molar heat capacity25.363 j/(mol·k)
    vapor pressure
    p (pa) 1 10 100 1 k 10 k 100 k
    at t (k) 500 552 617 704 813 958
    atomic properties
    oxidation states−2, −1, +1,[2] +2, +3, +4, +5, +6 (a strongly acidic oxide)
    electronegativitypauling scale: 2.55
    ionization energies
    • 1st: 941.0 kj/mol
    • 2nd: 2045 kj/mol
    • 3rd: 2973.7 kj/mol
    atomic radiusempirical: 120 pm
    covalent radius120±4 pm
    van der waals radius190 pm
    color lines in a spectral range
    spectral lines of selenium
    other properties
    natural occurrenceprimordial
    crystal structurehexagonal
    hexagonal crystal structure for selenium
    speed of sound thin rod3350 m/s (at 20 °c)
    thermal expansionamorphous: 37 µm/(m·k) (at 25 °c)
    thermal conductivityamorphous: 0.519 w/(m·k)
    magnetic orderingdiamagnetic[3]
    magnetic susceptibility−25.0·10−6 cm3/mol (298 k)[4]
    young's modulus10 gpa
    shear modulus3.7 gpa
    bulk modulus8.3 gpa
    poisson ratio0.33
    mohs hardness2.0
    brinell hardness736 mpa
    cas number7782-49-2
    history
    namingafter selene, greek goddess of the moon
    discovery and first isolationjöns jakob berzelius and johann gottlieb gahn (1817)
    main isotopes of selenium
    iso­tope abun­dance half-life (t1/2) decay mode pro­duct
    72se syn 8.4 d ε 72as
    γ
    74se 0.86% stable
    75se syn 119.8 d ε 75as
    γ
    76se 9.23% stable
    77se 7.60% stable
    78se 23.69% stable
    79se trace 3.27×105 y β 79br
    80se 49.80% stable
    82se 8.82% 1.08×1020 y ββ 82kr
    category category: selenium
    | references

    selenium is a chemical element with the symbol se and atomic number 34. it is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, and also has similarities to arsenic. it rarely occurs in its elemental state or as pure ore compounds in the earth's crust. selenium – from ancient greek σελήνη (selḗnē) "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).

    selenium is found in metal sulfide ores, where it partially replaces the sulfur. commercially, selenium is produced as a byproduct in the refining of these ores, most often during production. minerals that are pure selenide or selenate compounds are known but rare. the chief commercial uses for selenium today are glassmaking and pigments. selenium is a semiconductor and is used in photocells. applications in electronics, once important, have been mostly replaced with silicon semiconductor devices. selenium is still used in a few types of dc power surge protectors and one type of fluorescent quantum dot.

    selenium salts are toxic in large amounts, but trace amounts are necessary for cellular function in many organisms, including all animals. selenium is an ingredient in many multivitamins and other dietary supplements, including infant formula. it is a component of the antioxidant enzymes glutathione peroxidase and thioredoxin reductase (which indirectly reduce certain oxidized molecules in animals and some plants). it is also found in three deiodinase enzymes, which convert one thyroid hormone to another. selenium requirements in plants differ by species, with some plants requiring relatively large amounts and others apparently requiring none.[5]

  • characteristics
  • chemical compounds
  • history
  • occurrence
  • production
  • applications
  • biological role
  • see also
  • notes
  • references
  • external links

Selenium, 34Se
SeBlackRed.jpg
Selenium
Pronunciationm/ (LEE-nee-əm)
Appearanceblack, red, and gray (not pictured) allotropes
Standard atomic weight Ar, std(Se)78.971(8)[1]
Selenium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
S

Se

Te
arsenicseleniumbromine
Atomic number (Z)34
Groupgroup 16 (chalcogens)
Periodperiod 4
Blockp-block
Element category  Reactive nonmetal, sometimes considered a metalloid
Electron configuration[Ar] 3d10 4s2 4p4
Electrons per shell2, 8, 18, 6
Physical properties
Phase at STPsolid
Melting point494 K ​(221 °C, ​430 °F)
Boiling point958 K ​(685 °C, ​1265 °F)
Density (near r.t.)gray: 4.81 g/cm3
alpha: 4.39 g/cm3
vitreous: 4.28 g/cm3
when liquid (at m.p.)3.99 g/cm3
Critical point1766 K, 27.2 MPa
Heat of fusiongray: 6.69 kJ/mol
Heat of vaporization95.48 kJ/mol
Molar heat capacity25.363 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 500 552 617 704 813 958
Atomic properties
Oxidation states−2, −1, +1,[2] +2, +3, +4, +5, +6 (a strongly acidic oxide)
ElectronegativityPauling scale: 2.55
Ionization energies
  • 1st: 941.0 kJ/mol
  • 2nd: 2045 kJ/mol
  • 3rd: 2973.7 kJ/mol
Atomic radiusempirical: 120 pm
Covalent radius120±4 pm
Van der Waals radius190 pm
Color lines in a spectral range
Spectral lines of selenium
Other properties
Natural occurrenceprimordial
Crystal structurehexagonal
Hexagonal crystal structure for selenium
Speed of sound thin rod3350 m/s (at 20 °C)
Thermal expansionamorphous: 37 µm/(m·K) (at 25 °C)
Thermal conductivityamorphous: 0.519 W/(m·K)
Magnetic orderingdiamagnetic[3]
Magnetic susceptibility−25.0·10−6 cm3/mol (298 K)[4]
Young's modulus10 GPa
Shear modulus3.7 GPa
Bulk modulus8.3 GPa
Poisson ratio0.33
Mohs hardness2.0
Brinell hardness736 MPa
CAS Number7782-49-2
History
Namingafter Selene, Greek goddess of the moon
Discovery and first isolationJöns Jakob Berzelius and Johann Gottlieb Gahn (1817)
Main isotopes of selenium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
72Se syn 8.4 d ε 72As
γ
74Se 0.86% stable
75Se syn 119.8 d ε 75As
γ
76Se 9.23% stable
77Se 7.60% stable
78Se 23.69% stable
79Se trace 3.27×105 y β 79Br
80Se 49.80% stable
82Se 8.82% 1.08×1020 y ββ 82Kr
Category Category: Selenium
| references

Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, and also has similarities to arsenic. It rarely occurs in its elemental state or as pure ore compounds in the Earth's crust. Selenium – from Ancient Greek σελήνη (selḗnē) "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).

Selenium is found in metal sulfide ores, where it partially replaces the sulfur. Commercially, selenium is produced as a byproduct in the refining of these ores, most often during production. Minerals that are pure selenide or selenate compounds are known but rare. The chief commercial uses for selenium today are glassmaking and pigments. Selenium is a semiconductor and is used in photocells. Applications in electronics, once important, have been mostly replaced with silicon semiconductor devices. Selenium is still used in a few types of DC power surge protectors and one type of fluorescent quantum dot.

Selenium salts are toxic in large amounts, but trace amounts are necessary for cellular function in many organisms, including all animals. Selenium is an ingredient in many multivitamins and other dietary supplements, including infant formula. It is a component of the antioxidant enzymes glutathione peroxidase and thioredoxin reductase (which indirectly reduce certain oxidized molecules in animals and some plants). It is also found in three deiodinase enzymes, which convert one thyroid hormone to another. Selenium requirements in plants differ by species, with some plants requiring relatively large amounts and others apparently requiring none.[5]