Boron: Difference between revisions
imported>David E. Volk (→Elemental boron: -> Allotropes) |
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{{Elem_Infobox | {{Elem_Infobox | ||
|background1= | |background1=f2f2f2 | ||
|elementColor= | |align=right | ||
|elementColor=f2f2f2 | |||
|elName=Boron | |elName=Boron | ||
| | |elClass=Metalloid | ||
|eltrnCfg=1s<sup>2</sup>2s<sup>2</sup>2p<sup>1</sup> | |||
|elgroup=13 | |||
|eltrnCfg= | |elperiod=2 | ||
|elblock=p | |||
|no1= | |no1= | ||
|no2= | |no2= | ||
|no3= | |no3= | ||
|no4= | |no4= | ||
|properties= | |properties=High hardness metal | ||
|compounds=Oxides, halides and hydrides | |compounds=Oxides, halides and hydrides | ||
|uses=Reducing agents, Lewis acid catalysis, nuclear industry | |uses=Reducing agents, Lewis acid catalysis, nuclear industry, semi-conductor dopant | ||
|hazard= | |hazard=Boron hydrogen compounds (boranes) are toxic as well as highly flammable | ||
}} | }} | ||
'''Boron''' | '''Boron''' is a [[Chemical elements|chemical element]], typically found as a [[Solid_(state_of_matter)|solid]] in its elemental form. It has the [[chemical symbol]] B, [[atomic number]] (number of [[protons]]) ''Z'' = 5, and a [[Atomic mass#Standard atomic weights of the elements|standard atomic weight]] of 10.811 g/mol. | ||
Boron is a rare [[element]] present in only 0.0003% of the earth's crust, mostly found in dry lake beds in the western United States in the form of borax (Na<sub>2</sub>B<sub>4</sub>O<sub>5</sub>(OH)<sub>5</sub>•8H<sub>2</sub>O), and kernite (Na<sub>2</sub>B<sub>4</sub>O<sub>5</sub>(OH)<sub>5</sub>•2H<sub>2</sub>O), which are hydrated sodium salts of tetraboric acid. Borax is mildly alkaline and is used as a cleansing agent. In addition, due its low melting temperature, boron is used in flux for soldering and welding. Some boron compounds are [[Lewis acid-base theory|Lewis acids]] and elemental boron forms three-center two-electron bonds. Borohydrides are widely used as chemical reducing agents. | |||
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== Boric acids == | == Boric acids == | ||
[[Boric acid]], H<sub>3</sub>BO<sub>3</sub>, is a mildly acidic antiseptic compound formed from the reaction of borax with [[sulfuric acid]]. Boric acids include [[orthoboric acid]] (H<sub>3</sub>BO<sub>3</sub>), [[metaboric acid]] (HBO<sub>2</sub>) and [[tetraboric acid]], (H<sub>2</sub>B<sub>4</sub>O<sub>7</sub>), which is also called pyroboric acid. | [[Boric acid]], H<sub>3</sub>BO<sub>3</sub>, is a mildly acidic antiseptic compound formed from the reaction of borax with [[sulfuric acid]]. Boric acids include [[orthoboric acid]] (H<sub>3</sub>BO<sub>3</sub>), [[metaboric acid]] (HBO<sub>2</sub>) and [[tetraboric acid]], (H<sub>2</sub>B<sub>4</sub>O<sub>7</sub>), which is also called pyroboric acid. | ||
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== Boron hydrides == | == Boron hydrides == | ||
Boron hydrides are excellent sources of the [[hydride ion]] H<sup><b>-</b></sup> and thus are good [[reducing agent]]s. [[Sodium borohydride]], NaBH<sub>4</sub>, is a reducing agent used in many inorganic and organic reactions. [[Lithium borohydride]] (LiB<sub>4</sub>) and [[ | Boron hydrides are excellent sources of the [[hydride ion]] H<sup><b>-</b></sup> and thus are good [[reducing agent]]s. [[Sodium borohydride]], NaBH<sub>4</sub>, is a reducing agent used in many inorganic and organic reactions. [[Lithium borohydride]] (LiB<sub>4</sub>) and [[aluminium borohydride]] (Al(BH<sub>4</sub>)<sub>3</sub> are also common borohydrides used in chemistry. The reduction of ketones to secondary alcohols is a typical use for these reagents. Boron hydrides can fall into one of two categories, those with formula B<sub>n</sub>H<sub>n+4</sub> or the less stable formula B<sub>n</sub>H<sub>n+6</sub>. | ||
== Allotropes == | == Allotropes == | ||
Elemental boron exists in a number of allotropes. <math>alfa</math>-rhombohedral boron | Elemental boron exists in a number of allotropes. The simplest structure is <math>alfa</math>-rhombohedral boron. All forms are polyhedral clusters of boron atoms, are semi-conductors and are very hard materials. All forms of elemental boron contain both [[three-center two-electron bonds]] as well as the typical two-center two-electron bonds found in most molecules. | ||
== Stable isotopes == | == Stable isotopes == | ||
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== Nuclear industry == | == Nuclear industry == | ||
Both <sup>10</sup>B and <sup>11</sup>B are used in the nuclear industry. <sup>11</sup>B is used as a neutron reflector and <sup>10</sup>B is used in boron neutron capture therapy. Both isotopes can be used to synthesize the elements <sup>11</sup>C and <sup>13</sup>N. Unstable forms of boron include the following isotopes | Both <sup>10</sup>B and <sup>11</sup>B are used in the nuclear industry. <sup>11</sup>B is used as a neutron reflector and <sup>10</sup>B is used in boron neutron capture therapy. Both isotopes can be used to synthesize the elements <sup>11</sup>C and <sup>13</sup>N. Unstable forms of boron include the following isotopes: | ||
:<b>Radio-isotope atomic mass half-life (%)</b> | :<b>Radio-isotope atomic mass half-life (%)</b> | ||
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:<sup>12</sup>B 12.014352 0.0202 s <br> | :<sup>12</sup>B 12.014352 0.0202 s <br> | ||
:<sup>13</sup>B 13.017780 0.0174 s <br> | :<sup>13</sup>B 13.017780 0.0174 s <br> | ||
It is used for hardening metals in unspecified nuclear weapons.[[Category:Suggestion Bot Tag]] | |||
Latest revision as of 12:01, 20 July 2024
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Boron is a chemical element, typically found as a solid in its elemental form. It has the chemical symbol B, atomic number (number of protons) Z = 5, and a standard atomic weight of 10.811 g/mol.
Boron is a rare element present in only 0.0003% of the earth's crust, mostly found in dry lake beds in the western United States in the form of borax (Na2B4O5(OH)5•8H2O), and kernite (Na2B4O5(OH)5•2H2O), which are hydrated sodium salts of tetraboric acid. Borax is mildly alkaline and is used as a cleansing agent. In addition, due its low melting temperature, boron is used in flux for soldering and welding. Some boron compounds are Lewis acids and elemental boron forms three-center two-electron bonds. Borohydrides are widely used as chemical reducing agents.
Boric acids
Boric acid, H3BO3, is a mildly acidic antiseptic compound formed from the reaction of borax with sulfuric acid. Boric acids include orthoboric acid (H3BO3), metaboric acid (HBO2) and tetraboric acid, (H2B4O7), which is also called pyroboric acid.
Boron halides
All four boron trihalides are planar, non-polar, covalent compounds. Boron trifluoride is a gas, boron triiodide is a solid and boron trichloride and tribromide are liquids. Boron trihalides are Lewis acids and react readily with water to produce boric acid and the corresponding hydrogen halide.
Boron hydrides
Boron hydrides are excellent sources of the hydride ion H- and thus are good reducing agents. Sodium borohydride, NaBH4, is a reducing agent used in many inorganic and organic reactions. Lithium borohydride (LiB4) and aluminium borohydride (Al(BH4)3 are also common borohydrides used in chemistry. The reduction of ketones to secondary alcohols is a typical use for these reagents. Boron hydrides can fall into one of two categories, those with formula BnHn+4 or the less stable formula BnHn+6.
Allotropes
Elemental boron exists in a number of allotropes. The simplest structure is -rhombohedral boron. All forms are polyhedral clusters of boron atoms, are semi-conductors and are very hard materials. All forms of elemental boron contain both three-center two-electron bonds as well as the typical two-center two-electron bonds found in most molecules.
Stable isotopes
The standard atomic mass—the average over different isotopes weighted by abundance—of boron is 10.811 u, where u is the unified atomic mass unit. Boron has two stable isotopes:
- Isotope atomic mass natural abundance (%)
- 10B 10.012 937 0(4) 19.9(7)
- 11B 11.009 305 5(5) 80.1(7)
Nuclear industry
Both 10B and 11B are used in the nuclear industry. 11B is used as a neutron reflector and 10B is used in boron neutron capture therapy. Both isotopes can be used to synthesize the elements 11C and 13N. Unstable forms of boron include the following isotopes:
- Radio-isotope atomic mass half-life (%)
- 8B 8.024607 0.770 s
- 9B 9.013379 8 x 10-19 s
- 12B 12.014352 0.0202 s
- 13B 13.017780 0.0174 s
It is used for hardening metals in unspecified nuclear weapons.