Template:Infobox boron

Boron,  ₅B

boron (β-rhombohedral)
General properties
Name, symbol	boron, B
Appearance	black-brown
Allotropes	α-, β-rhombohedral, β-tetragonal (and more)
Pronunciation	/ˈbɔərɒn/
Boron in the periodic table
– ↑ B ↓ Al beryllium ← boron → carbon
Atomic number (Z)	5
Group, block	group 13, p-block
Period	period 2
Element category	metalloid
Standard atomic weight (Ar)	10.81 (10.806–10.821)
Electron configuration	[He] 2s2 2p1
per shell	2, 3
Physical properties
Phase	solid
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 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, −1, −5 ​(a mildly acidic oxide)
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
Miscellanea
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
Mohs hardness	~9.5
CAS Number	7440-42-8
History
Discovery	Joseph Louis Gay-Lussac and Louis Jacques Thénard (30 June 1808)
First isolation	Humphry Davy (9 July 1808)
Most stable isotopes of boron
iso NA half-life DM DE (MeV) DP 10B 19.9(7)% 10B is stable with 5 neutrons 11B 80.1(7)% 11B is stable with 6 neutrons
10B content may be as low as 19.1% and as high as 20.3% in natural samples. 11B is the remainder in such cases.

References

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