Technical data for Selenium

Overview Name Selenium Symbol Se Atomic Number 34 Atomic Weight 78.96 Density 4.819 g/cm3 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 27.2 MPa (268.4 Atm) Critical Temperature 1766 K Heat of Fusion 5.4 kJ/mol Heat of Vaporization 26 kJ/mol Heat of Combustion {"N/A", "N/A", "N/A"} J/(kg K) Specific Heat 321.2 J/(kg K)[note] Adiabatic Index N/A Neel Point N/A Thermal Conductivity 0.52 W/(m K) Thermal Expansion N/A Bulk physical properties Density 4.819 g/cm3 Density (Liquid) 3.99 g/cm3 Molar Volume 0.000016385 Brinell Hardness 736 MPa Mohs Hardness 2 MPa Vickers Hardness N/A Bulk Modulus 8.3 GPa Shear Modulus 3.7 GPa Young Modulus 10 GPa Poisson Ratio 0.33 Refractive Index 1.000895 Speed of Sound 3350 m/s Thermal Conductivity 0.52 W/(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[note] Heat of Combustion {"N/A", "N/A", "N/A"} J/(kg K) DOT Hazard Class {N/A, 6.1, N/A} DOT Numbers "N/A", {2658}, "N/A" EU Number {N/A, N/A, N/A} NFPA Fire Rating {N/A, 0, N/A} NFPA Hazards N/ A, N/ A, N/ A NFPA Health Rating {N/A, 2, N/A} NFPA Reactivity Rating {N/A, 0, N/A} RTECS Number {N/A, RTECSVS7700000, N/A} NFPA Label [note]

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 {CID6326970, CID6326970, CID139346} Gmelin Number {N/A, N/A, N/A} NSC Number {N/A, N/A, N/A} RTECS Number {N/A, RTECSVS7700000, N/A} 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%