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Boron Facts

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Boron
5B
Appearance
black-brown
General properties
Name, symbol, number boron, B, 5
Pronunciation /ˈbɔərɒn/
Metallic category metalloid
Group, period,block 13, 2, p
Standard atomic weight 10.81(1)
Electron configuration [He] 2s2 2p1
2, 3
Electron shells of boron (2, 3)
History
Discovery Joseph Louis Gay-Lussac and<énard">Louis Jacques Thénard[1](30 June 1808)
First isolation Humphry Davy[2] (9 July 1808)
Physical properties
Phase solid
Liquid density atm.p. 2.08 g·cm−3
Melting point 2349 K, 2076 °C, 3769 °F
Boiling point 4200 K, 3927 °C, 7101 °F
Heat of fusion 50.2 kJ·mol−1
Heat of vaporization 480 kJ·mol−1
Molar heat capacity 11.087 J·mol−1·K−1
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 2348 2562 2822 3141 3545 4072
Atomic properties
Oxidation states 3, 2, 1[3]
(mildly acidic oxide)
Electronegativity 2.04 (Pauling scale)
Ionization energies
(more)
1st: 800.6 kJ·mol−1
2nd: 2427.1 kJ·mol−1
3rd: 3659.7 kJ·mol−1
Atomic radius 90 pm
Covalent radius 84±3 pm
Van der Waals radius 192 pm
Miscellanea
Crystal structure rhombohedral
Boron has a rhombohedral crystal structure
Magnetic ordering diamagnetic[4]
Electrical resistivity (20 °C) ~106 Ω·m
Thermal conductivity 27.4 W·m−1·K−1
Thermal expansion (25 °C) (β form) 5–7[5]µm·m−1·K−1
Speed of sound(thin rod) (20 °C) 16,200 m·s−1
Mohs hardness ~9.5
CAS registry number 7440-42-8
Most stable isotopes
Main article: Isotopes of boron
iso NA half-life DM DE (MeV) DP
10B 19.9(7)%* 10B is stable with 5 neutrons[6]
11B 80.1(7)%* 11B is stable with 6 neutrons[6]
*Boron-10 content may be as low as 19.1% and as
high as 20.3% in natural samples. Boron-11 is
the remainder in such cases.[7]

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