Boron, 5 B Allotropes α-, β-rhombohedral, β-tetragonal (and more) Appearance black-brown – ↑B ↓ Al beryllium ← boron → carbon
Atomic number (Z ) 5 Group, period group 13 (boron group) , period 2 Block p-block Electron configuration {{{electron configuration}}} Electrons per shell
2, 3 Melting point 2349 K (2076 °C, 3769 °F) Boiling point 4200 K (3927 °C, 7101 °F) Density when liquid, at m.p. 2.08 g/cm3 Heat of fusion 50.2 kJ/mol Heat of vaporization 508 kJ/mol Molar heat capacity 11.087 J/(mol·K) Vapor pressure |- ! style="text-align:right;" | 10 B | style="text-align:right" | 20% | colspan="3" style="text-align:left;" | is stable |- ! style="text-align:right;" | 11 B | style="text-align:right" | 80%
| colspan="3" style="text-align:left;" | is stable P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 2348 2562 2822 3141 3545 4072
Electronegativity Pauling scale: 2.04 Ionization energies 1st: 800.6 kJ/mol 2nd: 2427.1 kJ/mol 3rd: 3659.7 kJ/mol (more) Atomic radius empirical: 90 pm Covalent radius 84±3 pm Van der Waals radius 192 pm Crystal structure rhombohedral Speed of sound thin rod 16,200 m/s (at 20 °C) Thermal expansion β form: 5–7 µm/(m·K) (at 25 °C) Thermal conductivity 27.4 W/(m·K) Electrical resistivity ~106 Ω·m (at 20 °C) Magnetic ordering diamagnetic Magnetic susceptibility (χ mol ) −6.7·10−6 cm3 /mol Mohs hardness ~9.5 CAS Number 7440-42-8 Discovery Joseph Louis Gay-Lussac and Louis Jacques Thénard (30 June 1808) First isolation Humphry Davy (9 July 1808) Isotope Abundance Half-life Decay mode Product
10 B content is 19.1–20.3% in natural samples, with the remainder being 11 B.| references | in Wikidata
بور
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