Template:Infobox boron

Boron,  ₅B

Template:Infobox element/symbol-to-top-image-caption
General properties
Pronunciation	Template:Infobox element/pronunciation
Allotropes	α-, β-rhombohedral, β-tetragonal (and more)
Appearance	black-brown
Standard atomic weight (Ar, standard)	Template:Infobox element/standard atomic weight
Mass number	Template:Infobox element/symbol-to-most-stable-isotope (most stable isotope)
Boron in the periodic table
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Atomic number (Z)	5
Group	Template:Infobox element/group
Period	period 2
Block	p-block
Element category	Template:Infobox element/category format
Electron configuration	[He] 2s2 2p1
Electrons per shell	2, 3
Physical properties
Phase at STP	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
[[Enthalpy of vaporization|Heat of Template:Engvar]]	508 kJ/mol
Molar heat capacity	11.087 J/(mol·K)
[[Vapor pressure|Template:Engvar pressure]] Template:Infobox element/vapor pressure table
Atomic properties
Oxidation states	Template:Infobox element/symbol-to-oxidation-state
Electronegativity	Pauling scale: 2.04
[[Ionization energy|Template:Engvar 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
Template:Infobox element/spectral lines
Other properties
Crystal structure	​Template:Infobox element/crystal structure Template:Infobox element/crystal structure
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	−6.7·10−6 cm3/mol
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)
Main isotopes of boron
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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.

Template:Infobox element/element navigation Template:Template reference list Five of these are named references. They may be cited in the containing article as

• <ref name="v1" /> for the source Infrared Emission Spectroscopy of BF and AIF
• <ref name="magnet" /> for the source from Handbook of Chemistry and Physics
• <ref name="NISTic" /> for the source Atomic Weights and Isotopic Compositions for All Elements
• <ref name="Lussac" /> for the source by Gay-Lussac
• <ref name="Davy" /> for the source by Davy