Technical data for Boron

Overview Name Boron Symbol B Atomic Number 5 Atomic Weight 10.811 Density 2.46 g/cm3 Melting Point 2075 °C Boiling Point 4000 °C Thermal properties Phase Solid Melting Point 2075 °C Boiling Point 4000 °C Absolute Melting Point 2348 K Absolute Boiling Point 4273 K Critical Pressure N/A Critical Temperature N/A Heat of Fusion 50 kJ/mol Heat of Vaporization 507 kJ/mol Heat of Combustion N/A Specific Heat 1030 J/(kg K)[note] Adiabatic Index N/A Neel Point N/A Thermal Conductivity 27 W/(m K) Thermal Expansion 6×10-6 K-1 Bulk physical properties Density 2.46 g/cm3 Density (Liquid) 2.08 g/cm3 Molar Volume 4.3947×10-6 Brinell Hardness N/A Mohs Hardness 9.3 MPa Vickers Hardness 4.9×104 MPa Bulk Modulus 320 GPa Shear Modulus N/A Young Modulus N/A Poisson Ratio N/A Refractive Index N/A Speed of Sound 1.62×104 m/s Thermal Conductivity 27 W/(m K) Thermal Expansion 6×10-6 K-1 Reactivity Valence 3 Electronegativity 2.04 ElectronAffinity 26.7 kJ/mol Ionization Energies 800.6, 2427.1, 3659.7, 25025.8, 32826.7 kJ/mol Health and Safety Autoignition Point N/A Flashpoint N/A Heat of Combustion N/A DOT Hazard Class N/A DOT Numbers N/A EU Number N/A NFPA Fire Rating 3 NFPA Hazards N/A NFPA Health Rating 2 NFPA Reactivity Rating 0 RTECS Classes Other RTECS Number RTECSED7350000 NFPA Label

Classifications Alternate Names None Names of Allotropes AlphaRhombohedralBoron, BetaRhombohedralBoron, AlphaTetragonalBoron Block p Group 13 Period 2 Electron Configuration [He]2s22p1 Color Black Discovery 1808 in France and United Kingdom Gas phase N/A CAS Number CAS7440-42-8 CID Number CID5462311 Gmelin Number N/A NSC Number N/A RTECS Number RTECSED7350000 Electrical properties Electrical Type Insulator Electrical Conductivity 0.0001 S/m Resistivity 10000 m Ω Superconducting Point N/A Magnetic properties Magnetic Type Diamagnetic Curie Point N/A Mass Magnetic Susceptibility -8.7×10-9 Molar Magnetic Susceptibility -9.41×10-11 Volume Magnetic Susceptibility -0.0000214 Abundances % in Universe 1×10-7% % in Sun 2×10-7% % in Meteorites 0.00016% % in Earth's Crust 0.00086% % in Oceans 0.00044% % in Humans 0.00007% Atomic dimensions and structure Atomic Radius 87 pm Covalent Radius 82 pm Van der Waals Radius N/A Crystal Structure Simple Trigonal Lattice Angles 1.01334, 1.01334, 1.01334 Lattice Constants 506, 506, 506 pm Space Group Name R_ 3m Space Group Number 166 Nuclear Properties Half-Life Stable Lifetime Stable Decay Mode N/A Quantum Numbers 2P1/2 Neutron Cross Section 755 Neutron Mass Absorption 2.4 Known Isotopes 6B, 7B, 8B, 9B, 10B, 11B, 12B, 13B, 14B, 15B, 16B, 17B, 18B, 19B Stable Isotopes 10B, 11B Isotopic Abundances 10B 19.9% 11B 80.1%