Template:Infobox selenium

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34 arsenic ← selenium → bromine S ↑ Se ↓ Te Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	selenium, Se, 34
Chemical series	nonmetals
Group, Period, Block	16, 4, p
Appearance	gray-black, metallic luster
Standard atomic weight	78.96(3)  g·mol−1
Electron configuration	[Ar] 4s2 3d10 4p4
Electrons per shell	2, 8, 18, 6
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
Melting point	494 K (221 °C, 430 °F)
Boiling point	958 K (685 °C, 1265 °F)
Critical point	1766 K, 27.2 MPa
Heat of fusion	(gray) 6.69  kJ·mol−1
Heat of vaporization	95.48  kJ·mol−1
Specific heat capacity	(25 °C) 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
Crystal structure	hexagonal
Oxidation states	6, 4, 2, 1,[1] -2 (strongly acidic oxide)
Electronegativity	2.55 (Pauling scale)
Ionization energies (more)	1st:  941.0  kJ·mol−1
	2nd:  2045  kJ·mol−1
	3rd:  2973.7  kJ·mol−1
Atomic radius	115  pm
Atomic radius (calc.)	103  pm
Covalent radius	116  pm
Van der Waals radius	190 pm
Miscellaneous
Magnetic ordering	no data
Thermal conductivity	(300 K) (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
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 registry number	7782-49-2
Selected isotopes
Main article: Isotopes of infobox selenium iso NA half-life DM DE (MeV) DP 72Se syn 8.4 d ε - 72As γ 0.046 - 74Se 0.87% 74Se is stable with 40 neutrons 75Se syn 119.779 d ε - 75As γ 0.264, 0.136, 0.279 - 76Se 9.36% 76Se is stable with 42 neutrons 77Se 7.63% 77Se is stable with 43 neutrons 78Se 23.78% 78Se is stable with 44 neutrons 79Se syn 2.95×105 y β- 0.151 79Br 80Se 49.61% 80Se is stable with 46 neutrons 82Se 8.73% 1.08×1020 y β-β- 2.995 82Kr
References