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black an reid allotropes
General properties
Name, seembol, nummer selenium, Se, 34
Pronunciation /sɨˈlniəm/ si-LEE-nee-əm
Element category polyatomic nonmetal
sometimes considered a metalloid
Group, period, block 16 (chalcogens), 4, p
Staundart atomic wicht 78.971(8)
Electron confeeguration [Ar] 3d10 4s2 4p4
2, 8, 18, 6
Electron shells of selenium (2, 8, 18, 6)
Namin after Selene, Greek goddess o the muin
Discovery Jöns Jakob Berzelius an Johann Gottlieb Gahn (1817)
First isolation Jöns Jakob Berzelius an Johann Gottlieb Gahn (1817)
Physical properties
Phase solid
Density (near r.t.) (gray) 4.81 g·cm−3
Density (near r.t.) (alpha) 4.39 g·cm−3
Density (near r.t.) (vitreous) 4.28 g·cm−3
Liquid density at m.p. 3.99 g·cm−3
Meltin pynt 494 K, 221 °C, 430 °F
Boilin pynt 958 K, 685 °C, 1265 °F
Creetical pynt 1766 K, 27.2 MPa
Heat o fusion (gray) 6.69 kJ·mol−1
Heat o vaporization 95.48 kJ·mol−1
Molar heat capacity 25.363 J·mol−1·K−1
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 6, 4, 2, 1,[1] -2
(strangly acidic oxide)
Electronegativity 2.55 (Pauling scale)
Ionization energies 1st: 941.0 kJ·mol−1
2nd: 2045 kJ·mol−1
3rd: 2973.7 kJ·mol−1
Atomic radius 120 pm
Covalent radius 120±4 pm
Van der Waals radius 190 pm
Crystal structure hexagonal
Selenium has a hexagonal crystal structure
Magnetic orderin diamagnetic[2]
Thermal conductivity (amorphous) 0.519 W·m−1·K−1
Thermal expansion (25 °C) (amorphous) 37 µm·m−1·K−1
Speed of sound (thin rod) (20 °C) 3350 m·s−1
Young's modulus 10 GPa
Shear modulus 3.7 GPa
Bulk modulus 8.3 GPa
Poisson ratio 0.33
Mohs hairdness 2.0
Brinell hairdness 736 MPa
CAS registry nummer 7782-49-2
Most stable isotopes
Main article: Isotopes o selenium
iso NA hauf-life DM DE (MeV) DP
72Se syn 8.4 d ε - 72As
γ 0.046 -
74Se 0.87% - (β+β+) 1.2094 74Ge
75Se syn 119.779 d ε - 75As
γ 0.264, 0.136,
76Se 9.36% 76Se is stable wi 42 neutrons
77Se 7.63% 77Se is stable wi 43 neutrons
78Se 23.78% 78Se is stable wi 44 neutrons
79Se trace 3.27×105 y β 0.151 79Br
80Se 49.61% - (ββ) 0.1339 80Kr
82Se 8.73% 1.08×1020 y ββ 2.995 82Kr
Decay modes in parentheses are predictit, but hae nae yet been observed
· r

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. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth–Heinemann. ISBN 0080379419. 
  2. 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.