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[[Category:Template:Pagetype with short description]]
Selenium, 34Se |
Selenium |
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Pronunciation | (Template:Respell) |
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Appearance | grey metallic-looking, red, and vitreous black (not pictured) allotropes |
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Standard atomic weight Ar, std(Se) | Template:Val[1] |
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Selenium in the periodic table |
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Atomic number (Z) | 34 |
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Group | group 16 (chalcogens) |
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Period | period 4 |
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Block | p-block |
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Electron configuration | [Ar] 3d10 4s2 4p4 |
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Electrons per shell | 2, 8, 18, 6 |
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Physical properties |
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Phase at STP | solid |
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Melting point | 494 K (221 °C, 430 °F) |
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Boiling point | 958 K (685 °C, 1265 °F) |
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Density (near r.t.) | gray: 4.81 g/cm3 alpha: 4.39 g/cm3 vitreous: 4.28 g/cm3 |
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when liquid (at m.p.) | 3.99 g/cm3 |
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Critical point | 1766 K, 27.2 MPa |
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Heat of fusion | gray: 6.69 kJ/mol |
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Heat of vaporization | 95.48 kJ/mol |
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Molar heat capacity | 25.363 J/(mol·K) |
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Vapor pressure
P (Pa)
|
1
|
10
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100
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1 k
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10 k
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100 k
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at T (K)
|
500
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552
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617
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704
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813
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958
|
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Atomic properties |
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Oxidation states | −2, −1, +1,[2] +2, +3, +4, +5, +6 (a strongly acidic oxide) |
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Electronegativity | Pauling scale: 2.55 |
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Ionization energies | - 1st: 941.0 kJ/mol
- 2nd: 2045 kJ/mol
- 3rd: 2973.7 kJ/mol
-
|
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Atomic radius | empirical: 120 pm |
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Covalent radius | 120±4 pm |
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Van der Waals radius | 190 pm |
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Spectral lines of selenium |
Other properties |
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Natural occurrence | primordial |
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Crystal structure | hexagonal |
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Speed of sound thin rod | 3350 m/s (at 20 °C) |
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Thermal expansion | amorphous: 37 µm/(m·K) (at 25 °C) |
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Thermal conductivity | amorphous: 0.519 W/(m·K) |
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Magnetic ordering | diamagnetic[3] |
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Magnetic susceptibility | −25.0·10−6 cm3/mol (298 K)[4] |
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Young's modulus | 10 GPa |
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Shear modulus | 3.7 GPa |
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Bulk modulus | 8.3 GPa |
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Poisson ratio | 0.33 |
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Mohs hardness | 2.0 |
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Brinell hardness | 736 MPa |
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CAS Number | 7782-49-2 |
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History |
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Naming | after Selene, Greek goddess of the moon |
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Discovery and first isolation | Jöns Jakob Berzelius and Johann Gottlieb Gahn (1817) |
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Main isotopes of selenium |
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Category: Selenium | references |
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References
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