This article is about the chemical element. For other uses, see Boron (disambiguation).
Chemical element, symbol B and atomic number 5
Boron, 5B
boron (β-rhombohedral)[1]
Boron
Pronunciation
/ˈbɔːrɒn/(BOR-on)
Allotropes
α-, β-rhombohedral, β-tetragonal (and more)
Appearance
black-brown
Standard atomic weight Ar°(B)
[10.806, 10.821][2]
10.81±0.02 (abridged)[3]
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
– ↑ B ↓ Al
beryllium ← boron → carbon
Atomic number (Z)
5
Group
group 13 (boron group)
Period
period 2
Block
p-block
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
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
−5, −1, 0,[4] +1, +2, +3[5][6] (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
Spectral lines of boron
Other properties
Natural occurrence
primordial
Crystal structure
rhombohedral
Thermal expansion
β form: 5–7 µm/(m⋅K) (at 25 °C)[7]
Thermal conductivity
27.4 W/(m⋅K)
Electrical resistivity
~106 Ω⋅m (at 20 °C)
Magnetic ordering
diamagnetic[8]
Molar magnetic susceptibility
−6.7×10−6 cm3/mol[8]
Speed of sound thin rod
16,200 m/s (at 20 °C)
Mohs hardness
~9.5
CAS Number
7440-42-8
History
Discovery
Joseph Louis Gay-Lussac and Louis Jacques Thénard[9] (30 June 1808)
First isolation
Humphry Davy[10] (9 July 1808)
Isotopes of boron
v
e
Main isotopes
Decay
abundance
half-life (t1/2)
mode
product
8B
synth
771.9 ms
β+
8Be
10B
19.6%
stable
11B
80.3%
stable
Category: Boron
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Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three valence electrons for forming covalent bonds, resulting in many compounds such as boric acid, the mineral sodium borate, and the ultra-hard crystals of boron carbide and boron nitride.
Boron is synthesized entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, so it is a low-abundance element in the Solar System and in the Earth's crust.[11] It constitutes about 0.001 percent by weight of Earth's crust.[12] It is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate minerals. These are mined industrially as evaporites, such as borax and kernite. The largest known deposits are in Turkey, the largest producer of boron minerals.
Elemental boron is a metalloid that is found in small amounts in meteoroids, but chemically uncombined boron is not otherwise found naturally on Earth. Industrially, the very pure element is produced with difficulty because of contamination by carbon or other elements that resist removal.[13] Several allotropes exist: amorphous boron is a brown powder; crystalline boron is silvery to black, extremely hard (about 9.5 on the Mohs scale), and a poor electrical conductor at room temperature. The primary use of the element itself is as boron filaments with applications similar to carbon fibers in some high-strength materials.
Boron is primarily used in chemical compounds. About half of all production consumed globally is an additive in fiberglass for insulation and structural materials. The next leading use is in polymers and ceramics in high-strength, lightweight structural and heat-resistant materials. Borosilicate glass is desired for its greater strength and thermal shock resistance than ordinary soda lime glass. As sodium perborate, it is used as a bleach. A small amount is used as a dopant in semiconductors, and reagent intermediates in the synthesis of organic fine chemicals. A few boron-containing organic pharmaceuticals are used or are in study. Natural boron is composed of two stable isotopes, one of which (boron-10) has a number of uses as a neutron-capturing agent.
The intersection of boron with biology is very small. Consensus on it as essential for mammalian life is lacking. Borates have low toxicity in mammals (similar to table salt) but are more toxic to arthropods and are occasionally used as insecticides. Boron-containing organic antibiotics are known. Although only traces are required, it is an essential plant nutrient.
^Van Setten et al. 2007, pp. 2460–1
^"Standard Atomic Weights: Boron". CIAAW. 2009.
^Prohaska T, Irrgeher J, Benefield J, Böhlke JK, Chesson LA, Coplen TB, et al. (4 May 2022). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
^Braunschweig H, Dewhurst RD, Hammond K, Mies J, Radacki K, Vargas A (2012). "Ambient-Temperature Isolation of a Compound with a Boron-Boron Triple Bond". Science. 336 (6087): 1420–2. Bibcode:2012Sci...336.1420B. doi:10.1126/science.1221138. PMID 22700924. S2CID 206540959.
^Zhang, K.Q., Guo, B., Braun, V., Dulick, M., Bernath, P.F. (1995). "Infrared Emission Spectroscopy of BF and AIF" (PDF). J. Molecular Spectroscopy. 170 (1): 82. Bibcode:1995JMoSp.170...82Z. doi:10.1006/jmsp.1995.1058.
^Schroeder, Melanie. Eigenschaften von borreichen Boriden und Scandium-Aluminium-Oxid-Carbiden(PDF) (in German). p. 139.
^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.
^ abHaynes, William M., ed. (2016). CRC Handbook of Chemistry and Physics (97th ed.). CRC Press. p. 4.127. ISBN 9781498754293.
^Gay Lussac, J.L., Thenard, L.J. (1808). "Sur la décomposition et la recomposition de l'acide boracique". Annales de chimie. 68: 169–174.
^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.
^"Q & A: Where does the element Boron come from?". physics.illinois.edu. Archived from the original on 29 May 2012. Retrieved 4 December 2011.
^"Boron". Britannica encyclopedia. Archived from the original on 4 August 2020. Retrieved 4 August 2020.
^Hobbs DZ, Campbell TT, Block FE (1964). Methods Used in Preparing Boron. U.S. Department of the Interior, Bureau of Mines. p. 14. Archived from the original on 8 March 2024. Retrieved 25 February 2022.
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