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Boron,  5B
Boron R105.jpg
boron (β-rhombohedral)[1]
General properties
Pronunciation/ˈbɔːrɒn/ (BOHR-on)
Allotropesα-, β-rhombohedral, β-tetragonal (and more)
Standard atomic weight (Ar, standard)[10.80610.821] conventional: 10.81
Boron in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Atomic number (Z)5
Groupgroup 13 (boron group)
Periodperiod 2
Element category  metalloid
Electron configuration[He] 2s2 2p1
Electrons per shell
2, 3
Physical properties
Phase at STPsolid
Melting point2349 K ​(2076 °C, ​3769 °F)
Boiling point4200 K ​(3927 °C, ​7101 °F)
Density when liquid (at m.p.)2.08 g/cm3
Heat of fusion50.2 kJ/mol
Heat of vaporization508 kJ/mol
Molar heat capacity11.087 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−5, −1, +1, +2, +3[2][3] (a mildly acidic oxide)
ElectronegativityPauling scale: 2.04
Ionization energies
  • 1st: 800.6 kJ/mol
  • 2nd: 2427.1 kJ/mol
  • 3rd: 3659.7 kJ/mol
  • (more)
Atomic radiusempirical: 90 pm
Covalent radius84±3 pm
Van der Waals radius192 pm
Color lines in a spectral range
Spectral lines of boron
Other properties
Natural occurrenceprimordial
Crystal structurerhombohedral
Rhombohedral crystal structure for boron
Speed of sound thin rod16,200 m/s (at 20 °C)
Thermal expansionβ form: 5–7 µm/(m·K) (at 25 °C)[4]
Thermal conductivity27.4 W/(m·K)
Electrical resistivity~106 Ω·m (at 20 °C)
Magnetic orderingdiamagnetic[5]
Magnetic susceptibility−6.7·10−6 cm3/mol[6]
Mohs hardness~9.5
CAS Number7440-42-8
DiscoveryJoseph Louis Gay-Lussac and Louis Jacques Thénard[7] (30 June 1808)
First isolationHumphry Davy[8] (9 July 1808)
Main isotopes of boron
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
10B 20% stable[9]
11B 80% stable[9]
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.[10]
| references
Boron in a tube

Boron is a chemical element. It has the chemical symbol B. It has the atomic number 5. It is a metalloid (it has properties of a metal and a non-metal). Much boron is found in chemical compounds in its ore borax. Boron is never found free in nature.

Two types of boron are found (allotropes). Amorphous boron is a brown powder and metallic (crystalline) boron is black and hard and a weak conductor at room temperature.

Pure boron is used as a dopant (a substance added to semiconductors to change how it behaves with electricity) in the semiconductor industry. Chemical compounds of boron are important as to make strong materials not weigh very much, as nontoxic insecticides and preservatives, and for chemical synthesis.

Plants need boron in them to live. Very small amounts of boron are needed in animal's bodies so that they are very healthy. How it keeps animals healthy is not known in a lot of detail.

Boron was discovered by Sir Humphry Davy, an English chemist, in 1808.

Boron melts at 2075 °C (3767 °F), and boils at 4000 °C (7232 °F).

References[change | change source]

  1. Van Setten et al. 2007, pp. 2460–1
  2. 2.0 2.1 Zhang, K.Q.; Guo, B.; Braun, V.; Dulick, M.; Bernath, P.F. (1995). "Infrared Emission Spectroscopy of BF and AIF". J. Molecular Spectroscopy 170: 82. doi:10.1006/jmsp.1995.1058. 
  3. Melanie Schroeder. "Eigenschaften von borreichen Boriden und Scandium-Aluminium-Oxid-Carbiden" (PDF) (in German). p. 139.
  4. Holcombe Jr., C. E.; Smith, D. D.; Lorc, J. D.; Duerlesen, W. K.; Carpenter; D. A. (October 1973). "Physical-Chemical Properties of beta-Rhombohedral Boron". High Temp. Sci. 5 (5): 349–57. 
  5. Lide, David R. (ed.) (2000). Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics (PDF). CRC press. ISBN 0849304814.CS1 maint: Extra text: authors list (link)
  6. Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
  7. Gay Lussac, J.L.; Thenard, L.J. (1808). "Sur la décomposition et la recomposition de l'acide boracique". Annales de chimie 68: 169–174. 
  8. Davy H (1809). "An account of some new analytical researches on the nature of certain bodies, particularly the alkalies, phosphorus, sulphur, carbonaceous matter, and the acids hitherto undecomposed: with some general observations on chemical theory". Philosophical Transactions of the Royal Society of London 99: 39–104. doi:10.1098/rstl.1809.0005. 
  9. 9.0 9.1 "Atomic Weights and Isotopic Compositions for All Elements". National Institute of Standards and Technology. Retrieved 2008-09-21.
  10. Szegedi, S.; Váradi, M.; Buczkó, Cs. M.; Várnagy, M.; Sztaricskai, T. (1990). "Determination of boron in glass by neutron transmission method". Journal of Radioanalytical and Nuclear Chemistry Letters 146 (3): 177. doi:10.1007/BF02165219. 
  11. Melanie Schroeder. "Eigenschaften von borreichen Boriden und Scandium-Aluminium-Oxid-Carbiden" (PDF) (in German). p. 139.