Technical data for Selenium

Overview
NameSelenium
SymbolSe
Atomic Number34
Atomic Weight78.96
Density4.819 g/cm3
Melting Point221 °C[note]
Boiling Point685 °C

Thermal properties
PhaseSolid
Melting Point221 °C[note]
Boiling Point685 °C
Absolute Melting Point494 K[note]
Absolute Boiling Point958 K
Critical Presure27.2 MPa (268.4 Atm)
Critical Temperature1766 K
Heat of Fusion5.4 kJ/mol
Heat of Vaporization26 kJ/mol
Heat of CombustionN/A
Specific Heat321.2 J/(kg K)[note]
Thermal Conductivity0.52 W/(m K)
Thermal ExpansionN/A

Bulk physical properties
Density4.819 g/cm3
Density (Liquid)3.99 g/cm3
Molar Volume0.000016385
Brinell Hardness736 MPa
Mohs Hardness2 MPa
Bulk Modulus8.3 GPa
Shear Modulus3.7 GPa
Young Modulus10 GPa
Poisson Ratio0.33
Refractive Index1.000895
Speed of Sound3350 m/s
Thermal Conductivity0.52 W/(m K)
Thermal ExpansionN/A

Reactivity
Valence6
Electronegativity2.55
ElectronAffinity195 kJ/mol
Ionization Energies
941, 2045, 2973.7, 4144, 6590, 7880, 14990 kJ/mol

Health and Safety
Autoignition PointN/A
FlashpointN/A

Classifications
Alternate NamesNone
Nams of Allotropes
AmorphousRedSelenium, AmorphousBlackSelenium, MonoclinicSelenium, HexagonalSelenium
Blockp
Group16
Period4
Electron Configuration[Ar]3d104s24p4
ColorGray
Discovery
1817 in Sweden
Gas phaseN/A
CAS NumberCAS7782-49-2

Electrical properties
Electrical TypeN/A
Electrical ConductivityN/A
ResistivityN/A
Superconducting PointN/A

Magnetic properties
Magnetic TypeDiamagnetic
Mass Magnetic Susceptibility-4×10-9
Molar Magnetic Susceptibility-3.16×10-10
Volume Magnetic Susceptibility-0.0000193

Abundances
% in Universe3×10-6%
% in SunN/A
% in Meteorites0.0013%
% in Earth's Crust5×10-6%
% in Oceans4.5×10-8%
% in Humans5×10-6%

Atomic dimensions and structure
Atomic Radius103 pm
Covalent Radius116 pm
Van der Waals Radius190 pm
Crystal StructureSimple Monoclinic
Lattice Angles
π/2, 1.58493, π/2
Lattice Constants
905.4, 908.3, 1160.1 pm
Space Group NameP121/c1
Space Group Number14

Nuclear Properties
Half-LifeStable
LifetimeStable
Stable Isotopes
74Se, 76Se, 77Se, 78Se, 80Se
Isotopic Abundances
74Se0.89%
76Se9.37%
77Se7.63%
78Se23.77%
80Se49.61%
82Se8.73%

Notes on the properties of Selenium:
Absolute Melting Point: Value given for hexagonal, gray form.
Melting Point: Value given for hexagonal, gray form.
Specific Heat: Value given for solid hexagonal form.