Boron

Boron
	5B
	-; ↑; B; ↓; Al
	beryllium ← boron → carbon
	Boron in the periodic table
Appearance
	black-brown; ; Boron, shown here in the form of its β-rhombohedral phase (its most thermodynamically stable allotrope)
General properties
Name, symbol, number	boron, B, 5
Pronunciation	/ˈbɔːrɒn/
Element category	metalloid
Group, period, block	Template:Infobox element/group, 2, p
Standard atomic weight	10.81(1)
Electron configuration	[He] 2s2 2p1; 2, 3
Physical properties
Phase	solid
Liquid density at m.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
[[Enthalpy of vaporization\|Heat of Template:Engvar]]	508 kJ·mol−1
Molar heat capacity	11.087 J·mol−1·K−1
[[Vapor pressure\|Template:Engvar pressure]]
Atomic properties
Oxidation states	3, 2, 1; (mildly acidic oxide)
Electronegativity	2.04 (Pauling scale)
[[ionization energy\|Template:Engvar 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	Template:Infobox element/crystal structure wikilink
Magnetic ordering	diamagnetic
Electrical resistivity	(20 °C) ~106 Ω·m
Thermal conductivity	27.4 W·m−1·K−1
Thermal expansion	(25 °C) (β form) 5–7 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
History
Discovery	Joseph Louis Gay-Lussac and Louis Jacques Thénard (30 June 1808)
First isolation	Humphry Davy (9 July 1808)
Most stable isotopes
	Main article: Isotopes of boron
	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.
	v; t; e; · references