Template:Infobox selenium

arsenic ← selenium → bromine S ↑ Se ↓ Te 34Se Periodic table
Appearance
Black and red allotropes
General properties
Name, symbol, number	selenium, Se, 34
Pronunciation	/sɨˈliːniəm/ si-LEE-nee-əm
Element category	nonmetal
Group, period, block	16, 4, p
Standard atomic weight	78.96
Electron configuration	[Ar] 4s2 3d10 4p4
Electrons per shell	2, 8, 18, 6 (Image)
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
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, -2 (strongly 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
Miscellanea
Crystal structure	hexagonal
Magnetic ordering	diamagnetic
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 hardness	2.0
Brinell hardness	736 MPa
CAS registry number	7782-49-2
Most stable isotopes
Main article: Isotopes of 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 trace 3.27×105 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

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