Selenium

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Selenium, 34Se
Template:Infobox element/symbol-to-top-image/alt
Selenium
Pronunciation/sɪˈlniəm/ (sih-LEE-nee-əm)
Appearanceblack an reid allotropes
Standard atomic weight Ar, std(Se)78.971(8)[1]
Selenium in the periodic cairt
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 Airn Cobalt Nickel Capper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Siller (element) 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 Gowd Mercur (element) Thallium Leid (element) 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 Ununtrium Flerovium Ununpentium Livermorium Ununseptium Ununoctium
S

Se

Te
arsenicseleniumbromine
Atomic nummer (Z)34
Groupgroup 16 (chalcogens)
Periodperiod 4
Blockp-block
Element category  Reactive nonmetal
Electron confeeguration[Ar] 3d10 4s2 4p4
Electrons per shell2, 8, 18, 6
Pheesical properties
Phase at STPsolit
Meltin pynt494 K ​(221 °C, ​430 °F)
Bylin pynt958 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
Creetical pynt1766 K, 27.2 MPa
Heat o fusion(gray) 6.69 kJ/mol
Heat o vapourisation95.48 kJ/mol
Molar heat capacity25.363 J/(mol·K)
Vapour pressur
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 strangly acidic
ElectronegativityPauling scale: 2.55
Atomic radiusempirical: 120 pm
Covalent radius120±4 pm
Van der Waals radius190 pm
Colour lines in a spectral range
Spectral lines o selenium
Ither properties
Naitural occurrenceprimordial
Creestal structurhexagonal
Hexagonal creestal structur for selenium
Speed o soond thin rod3350 m/s (at 20 °C)
Thermal expansion(amorphous) 37 µm/(m·K) (at 25 °C)
Thermal conductivity(amorphous) 0.519 W/(m·K)
Magnetic orderindiamagnetic[3]
Young's modulus10 GPa
Shear modulus3.7 GPa
Bulk modulus8.3 GPa
Poisson ratio0.33
Mohs haurdness2.0
Brinell haurdness736 MPa
CAS Nummer7782-49-2
History
DiskiveryJöns Jakob Berzelius an Johann Gottlieb Gahn (1817)
First isolationJöns Jakob Berzelius an Johann Gottlieb Gahn (1817)
Main isotopes o selenium
Iso­tope Abun­dance Hauf-life (t1/2) Decay mode Pro­duct
72Se syn 8.4 d ε 72As
γ -
74Se 0.87% - (β+β+) 74Ge
75Se syn 119.779 d ε 75As
γ -
76Se 9.36% stable
77Se 7.63% stable
78Se 23.78% stable
79Se trace 3.27×105 y β 79Br
80Se 49.61% - (ββ) 80Kr
82Se 8.73% 1.08×1020 y ββ 82Kr
Decay modes in parentheses are predictit, but hae nae yet been observed
| references

Selenium is a chemical element wi seembol Se an atomic nummer 34. It is a nonmetal wi properties that are intermediate atween those o its periodic cairt column-adjacent chalcogen elements sulphur an tellurium. It rarely occurs in its elemental state in naitur, or as pure ore compoonds. Selenium (Greek σελήνη selene meanin "Muin") wis discovered in 1817 bi Jöns Jacob Berzelius, who notit the seemilarity o the new element tae the previously kent tellurium (named for the Yird).

References[eedit | eedit soorce]

  1. Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.
  2. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth–Heinemann. ISBN 0080379419.
  3. Magnetic susceptibility of the elements and inorganic compounds, in Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
  4. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth–Heinemann. ISBN 0080379419.