Technical data for Selenium

Overview Name Selenium Symbol Se Atomic Number 34 Atomic Weight 78.96 Density 4.819 g/cc Melting Point 221.°C[note] Boiling Point 685.°C Thermal properties Phase Solid Melting Point 221.°C[note] Boiling Point 685.°C Absolute Melting Point 494.K[note] Absolute Boiling Point 958.K Critical Pressure 27.2MPa (268.4Atm) Critical Temperature 1766.K Heat of Fusion 5.4KJ/mol Heat of Vaporization 26.KJ/mol Heat of Combustion N/A Specific Heat 321.2J/(Kg K)[note] Adiabatic Index N/A Neel Point N/A Thermal Conductivity 0.52W/(m K) Thermal Expansion N/A Bulk physical properties Density 4.819 g/cc Density (Liquid) 3.99 g/cc Molar Volume 0.000016385 Brinell Hardness 736.MPa Mohs Hardness 2.MPa Vickers Hardness N/A Bulk Modulus 8.3GPa Shear Modulus 3.7GPa Young Modulus 10.GPa Poisson Ratio 0.33 Refractive Index 1.000895 Speed of Sound 3350.m/s Thermal Conductivity 0.52W/(m K) Thermal Expansion N/A Reactivity Valence 6 Electronegativity 2.55 ElectronAffinity 195.KJ/mol Ionization Energies 941., 2045., 2973.7, 4144., 6590., 7880., 14990. KJ/mol Health and Safety Autoignition Point N/A Flashpoint N/A Heat of Combustion N/A DOT Hazard Class 6.1 DOT Numbers 2658 EU Number EU231-957-4 NFPA Fire Rating 0 NFPA Hazards N/A NFPA Health Rating 2 NFPA Reactivity Rating 0 RTECS Classes Tumorigen, Reproductive Effector RTECS Number RTECSVS7700000 NFPA Label

Classifications Alternate Names None Names of Allotropes AmorphousRedSelenium, AmorphousBlackSelenium, MonoclinicSelenium, HexagonalSelenium Block p Group 16 Period 4 Electron Configuration [Ar]3d104s24p4 Color Gray Discovery 1817 in Sweden Gas phase N/A CAS Number CAS7782-49-2 CID Number CID107674 Gmelin Number Gmelin8872 NSC Number NSC605850 RTECS Number RTECSVS7700000 Electrical properties Electrical Type N/A Electrical Conductivity N/A Resistivity N/A Superconducting Point N/A Magnetic properties Magnetic Type Diamagnetic Curie Point N/A Mass Magnetic Susceptibility -4.×10-9 Molar Magnetic Susceptibility -3.16×10-10 Volume Magnetic Susceptibility -0.0000193 Abundances % in Universe 3.×10-6% % in Sun N/A % in Meteorites 0.0013% % in Earth's Crust 5.×10-6% % in Oceans 4.5×10-8% % in Humans 5.×10-6% Atomic dimensions and structure Atomic Radius 103.pm Covalent Radius 116.pm Van der Waals Radius 190.pm Crystal Structure Simple Monoclinic Lattice Angles π/2, 1.58493, π/2 Lattice Constants 905.4, 908.3, 1160.1 pm Space Group Name P121/c1 Space Group Number 14 Nuclear Properties Half-Life Stable Lifetime Stable Decay Mode N/A Quantum Numbers 3P2 Neutron Cross Section 11.7 Neutron Mass Absorption 0.0056 Known Isotopes 65Se, 66Se, 67Se, 68Se, 69Se, 70Se, 71Se, 72Se, 73Se, 74Se, 75Se, 76Se, 77Se, 78Se, 79Se, 80Se, 81Se, 82Se, 83Se, 84Se, 85Se, 86Se, 87Se, 88Se, 89Se, 90Se, 91Se, 92Se, 93Se, 94Se Stable Isotopes 74Se, 76Se, 77Se, 78Se, 80Se Isotopic Abundances 74Se 0.89% 76Se 9.37% 77Se 7.63% 78Se 23.77% 80Se 49.61% 82Se 8.73%