Template:Infobox selenium

Selenium,  ₃₄Se

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General properties
Pronunciation	Template:Infobox element/pronunciation
Appearance	black, red, and gray (not pictured) allotropes
Standard atomic weight (Ar, standard)	Template:Infobox element/standard atomic weight
Mass number	Template:Infobox element/symbol-to-most-stable-isotope (most stable isotope)
Selenium in the periodic table
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Atomic number (Z)	34
Group	Template:Infobox element/group
Period	period 4
Block	p-block
Element category	Template:Infobox element/category format, sometimes considered a metalloid
Electron configuration	[Ar] 3d10 4s2 4p4
Electrons per shell	2, 8, 18, 6
Physical properties
Phase at STP	solid
Melting point	494 K ​(221 °C, ​430 °F)
Boiling point	958 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 point	1766 K, 27.2 MPa
Heat of fusion	gray: 6.69 kJ/mol
[[Enthalpy of vaporization|Heat of Template:Engvar]]	95.48 kJ/mol
Molar heat capacity	25.363 J/(mol·K)
[[Vapor pressure|Template:Engvar pressure]] Template:Infobox element/vapor pressure table
Atomic properties
Oxidation states	Template:Infobox element/symbol-to-oxidation-state
Electronegativity	Pauling scale: 2.55
[[Ionization energy|Template:Engvar energies]]	1st: 941.0 kJ/mol 2nd: 2045 kJ/mol 3rd: 2973.7 kJ/mol
Atomic radius	empirical: 120 pm
Covalent radius	120±4 pm
Van der Waals radius	190 pm
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Other properties
Crystal structure	​Template:Infobox element/crystal structure Template:Infobox element/crystal structure
Speed of sound thin rod	3350 m/s (at 20 °C)
Thermal expansion	amorphous: 37 µm/(m·K) (at 25 °C)
Thermal conductivity	amorphous: 0.519 W/(m·K)
Magnetic ordering	diamagnetic
Magnetic susceptibility	−25.0·10−6 cm3/mol (298 K)
Young's modulus	10 GPa
Shear modulus	3.7 GPa
Bulk modulus	8.3 GPa
Poisson ratio	0.33
Mohs hardness	2.0
Brinell hardness	736 MPa
CAS Number	7782-49-2
History
Naming	after Selene, Greek goddess of the moon
Discovery and first isolation	Jöns Jakob Berzelius and Johann Gottlieb Gahn (1817)
Main isotopes of selenium
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