boron (β-rhombohedral) [1] |
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Pronunciation | (BOR-on) |
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Allotropes | α-, β-rhombohedral, β-tetragonal (and more) |
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Appearance | black-brown |
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Group | group 13 (boron group) |
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Period | period 2 |
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Block | p-block |
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Electron configuration | [He] 2s2 2p1 |
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Electrons per shell | 2, 3 |
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Phase at STP | solid |
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Melting point | 2349 K (2076 °C, 3769 °F) |
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Boiling point | 4200 K (3927 °C, 7101 °F) |
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Density when liquid (at m.p.) | 2.08 g/cm3 |
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Heat of fusion | 50.2 kJ/mol |
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Heat of vaporization | 508 kJ/mol |
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Molar heat capacity | 11.087 J/(mol·K) |
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Vapor pressure
P (Pa) |
1 |
10 |
100 |
1 k |
10 k |
100 k |
at T (K) |
2348 |
2562 |
2822 |
3141 |
3545 |
4072 |
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Oxidation states | −5, −1, 0,[4] +1, +2, +3[5][6] (a mildly acidic oxide) |
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Electronegativity | Pauling scale: 2.04 |
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Ionization energies | - 1st: 800.6 kJ/mol
- 2nd: 2427.1 kJ/mol
- 3rd: 3659.7 kJ/mol
- (more)
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Atomic radius | empirical: 90 pm |
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Covalent radius | 84±3 pm |
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Van der Waals radius | 192 pm |
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Spectral lines of boron |
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Natural occurrence | primordial |
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Crystal structure | rhombohedral |
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Thermal expansion | β form: 5–7 µm/(m⋅K) (at 25 °C)[7] |
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Thermal conductivity | 27.4 W/(m⋅K) |
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Electrical resistivity | ~106 Ω⋅m (at 20 °C) |
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Magnetic ordering | diamagnetic[8] |
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Speed of sound thin rod | 16,200 m/s (at 20 °C) |
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Mohs hardness | ~9.5 |
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CAS Number | 7440-42-8 |
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Category: Boron | references |