Difference between revisions of "Boron"

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{{Infobox element
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<!-- General properties -->
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|name=Boron
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|symbol=B
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|pronounce=
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|pronounce ref=
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|pronounce comment=
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|pronounce 2=
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|alt name=
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|alt names=
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|allotropes=α-, β-rhombohedral, α-, β-tetragonal, γ-orthorhombic, Amorphous
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|appearance=Black-brownish solid
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<!-- Periodic table -->
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|above=
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|below=[[Aluminium|Al]]
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|left=[[Beryllium]]
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|right=[[Carbon]]
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|number=5
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|atomic mass=10.81
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|atomic mass 2=
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|atomic mass ref=
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|atomic mass comment=
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|series=
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|series ref=
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|series comment=
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|series color=
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|group= 13
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|group ref=
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|group comment=(boron group)
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|period=2
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|period ref=
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|period comment=
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|block=p
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|block ref=
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|block comment=
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|electron configuration=[He] 2s<sup>2</sup> 2p<sup>1</sup>
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|electron configuration ref=
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|electron configuration comment=
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|electrons per shell=2, 3
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|electrons per shell ref=
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|electrons per shell comment=
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<!-- Physical properties -->
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|physical properties comment=
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|color=Black or brown
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|phase=Solid
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|phase ref=
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|phase comment=
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|melting point K=2349
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|melting point C=2076
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|melting point F=3769
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|melting point ref=
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|melting point comment=
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|boiling point K=4200
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|boiling point C=3927
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|boiling point F=​7101
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|boiling point ref=
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|boiling point comment=
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|sublimation point K=
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|sublimation point C=
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|sublimation point F=
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|sublimation point ref=
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|sublimation point comment=
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|density gplstp=
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|density gplstp ref=
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|density gplstp comment=
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|density gpcm3nrt=
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|density gpcm3nrt ref=
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|density gpcm3nrt comment=2.46 g/cm<sup>3</sup> (α-rhombohedral)<br>2.35 g/cm<sup>3</sup> (β-rhombohedral)<br>2.52 (γ-orthorhombic) g/cm<sup>3</sup><br>2.36 g/cm<sup>3</sup> (β-tetragonal)
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|density gpcm3nrt 2=
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|density gpcm3nrt 3=
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|density gpcm3nrt 3 comment=
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|density gpcm3mp=2.08
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|density gpcm3mp ref=
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|density gpcm3mp comment=
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|density gpcm3bp=
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|density gpcm3bp ref=
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|density gpcm3bp comment=
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|molar volume=
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|molar volume unit =
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|molar volume ref=
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|molar volume comment=
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|triple point K=
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|triple point kPa=
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|triple point ref=
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|triple point comment=
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|triple point K 2=
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|triple point kPa 2=
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|triple point 2 ref=
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|triple point 2 comment=
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|critical point K=
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|critical point MPa=
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|critical point ref=
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|critical point comment=
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|heat fusion=50.2
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|heat fusion ref=
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|heat fusion comment=
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|heat fusion 2=
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|heat fusion 2 ref=
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|heat fusion 2 comment=
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|heat vaporization=508
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|heat vaporization ref=
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|heat vaporization comment=
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|heat capacity=11.087
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|heat capacity ref=
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|heat capacity comment=
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|heat capacity 2=
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|heat capacity 2 ref=
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|heat capacity 2 comment=
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|vapor pressure 1=2348
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|vapor pressure 10=2562
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|vapor pressure 100=2822
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|vapor pressure 1 k=3141
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|vapor pressure 10 k=3545
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|vapor pressure 100 k=4072
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|vapor pressure ref=
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|vapor pressure comment=
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|vapor pressure 1 2=
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|vapor pressure 10 2=
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|vapor pressure 100 2=
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|vapor pressure 1 k 2=
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|vapor pressure 10 k 2=
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|vapor pressure 100 k 2=
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|vapor pressure 2 ref=
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|vapor pressure 2 comment=
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<!-- Atomic properties -->
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|atomic properties comment=
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|oxidation states='''3''', 2, 1, −1, −5​
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|oxidation states ref=
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|oxidation states comment=(a mildly acidic oxide)
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|electronegativity=2.04
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|electronegativity ref=
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|electronegativity comment=
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|ionization energy 1=800.6
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|ionization energy 1 ref=
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|ionization energy 1 comment=
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|ionization energy 2=2427.1
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|ionization energy 2 ref=
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|ionization energy 2 comment=
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|ionization energy 3=3659.7
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|ionization energy 3 ref=
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|ionization energy 3 comment=
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|number of ionization energies=
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|ionization energy ref=
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|ionization energy comment=
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|atomic radius=90
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|atomic radius ref=
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|atomic radius comment=
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|atomic radius calculated=
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|atomic radius calculated ref=
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|atomic radius calculated comment=
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|covalent radius=84±3
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|covalent radius ref=
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|covalent radius comment=
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|Van der Waals radius=192
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|Van der Waals radius ref=
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|Van der Waals radius comment=
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<!-- Miscellanea -->
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|crystal structure=
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|crystal structure prefix=
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|crystal structure ref=
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|crystal structure comment= Rhombohedral
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|crystal structure 2=
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|crystal structure 2 prefix=
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|crystal structure 2 ref=
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|crystal structure 2 comment=
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|speed of sound=
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|speed of sound ref=
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|speed of sound comment=
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|speed of sound rod at 20=16,200
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|speed of sound rod at 20 ref=
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|speed of sound rod at 20 comment=
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|speed of sound rod at r.t.=
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|speed of sound rod at r.t. ref=
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|speed of sound rod at r.t. comment=
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|thermal expansion=
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|thermal expansion ref=
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|thermal expansion comment=
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|thermal expansion at 25=β form: 5–7
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|thermal expansion at 25 ref=
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|thermal expansion at 25 comment=
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|thermal conductivity=27.4
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|thermal conductivity ref=
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|thermal conductivity comment=
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|thermal conductivity 2=
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|thermal diffusivity=
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|electrical resistivity=
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|electrical resistivity comment=
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|electrical resistivity at 0=
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|electrical resistivity at 0 ref=
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|electrical resistivity at 0 comment=
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|electrical resistivity at 20=~10<sup>6</sup>
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|electrical resistivity at 20 ref=
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|electrical resistivity at 20 comment=
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|band gap=
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|band gap ref=
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|band gap comment=
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|Curie point K=
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|magnetic ordering=
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|magnetic ordering ref=
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|magnetic ordering comment=
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|tensile strength=
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|Young's modulus=
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|Young's modulus comment=
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|Shear modulus=
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|Shear modulus ref=
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|Shear modulus comment=
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|Bulk modulus=185 GPa (α-rhombohedral)<br>224 GPa (β-rhombohedral)<br>227 GPa (γ-orthorhombic)
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|Bulk modulus ref=
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|Bulk modulus comment=
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|Poisson ratio=
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|Mohs hardness=
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|Mohs hardness ref=
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|Mohs hardness comment=
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|Mohs hardness 2=
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|Mohs hardness 2 ref=
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|Mohs hardness 2 comment=
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|Vickers hardness=
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|Vickers hardness ref=
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|Vickers hardness comment=42 GPa (α-rhombohedral)<br>45 GPa (β-rhombohedral)<br>50–58 GPa (γ-orthorhombic)
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|Brinell hardness=
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|Brinell hardness ref=
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|Brinell hardness comment=
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|CAS number=7440-42-8
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|CAS number ref=
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|CAS number comment=
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<!-- History -->
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|naming=
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|predicted by=
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|prediction date ref=
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|prediction date=
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|discovered by= Joseph Louis Gay-Lussac and Louis Jacques Thénard
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|discovery date ref=
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|discovery date=30 June 1808
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|first isolation by= Humphry Davy
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|first isolation date ref=
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|first isolation date=9 July 1808
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|discovery and first isolation by=
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|named by=
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|named date ref=
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|named date=
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|history comment label=
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<!-- Isotopes -->
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|isotopes=
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|isotopes comment=
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|engvar=
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}}
 
'''Boron''' is a [[metalloid]] with symbol '''B''' and atomic number 5. It is a black solid, resistant to most chemicals at room temperature.
 
'''Boron''' is a [[metalloid]] with symbol '''B''' and atomic number 5. It is a black solid, resistant to most chemicals at room temperature.
  

Revision as of 17:26, 2 October 2017

Boron,  5B
General properties
Name, symbol Boron, B
Allotropes α-, β-rhombohedral, α-, β-tetragonal, γ-orthorhombic, Amorphous
Appearance Black-brownish solid
Boron in the periodic table

↑
B
↓
Al
Beryllium ← Boron → Carbon
Atomic number 5
Standard atomic weight (Ar) 10.81
Group, block (boron group); p-block
Period period 2
Electron configuration [He] 2s2 2p1
per shell
 2, 3
Physical properties
Black or brown
Phase Solid
Melting point 2349 K ​(2076 °C, ​3769 °F)
Boiling point 4200 K ​(3927 °C, ​​7101 °F)
Density when liquid, at  2.08 g/cm3
Heat of fusion 50.2 kJ/mol
Heat of 508 kJ/mol
Molar heat capacity 11.087 J/(mol·K)
 pressure
Atomic properties
Oxidation states 3, 2, 1, −1, −5​ ​(a mildly acidic oxide)
Electronegativity Pauling scale: 2.04
energies 1st: 800.6 kJ/mol
2nd: 2427.1 kJ/mol
3rd: 3659.7 kJ/mol
Atomic radius empirical: 90 pm
Covalent radius 84±3 pm
Van der Waals radius 192 pm
Miscellanea
Crystal structure ​Rhombohedral
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)
Bulk modulus 185 GPa (α-rhombohedral)
224 GPa (β-rhombohedral)
227 GPa (γ-orthorhombic) GPa
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)
· references

Boron is a metalloid with symbol B and atomic number 5. It is a black solid, resistant to most chemicals at room temperature.

Properties

Chemical

Boron's chemical properties are closer to silicon than to aluminium, the element next in group. Crystalline boron is chemically inert and resistant to attack by hot hydrohalic acids, such as hydrochloric acid and hydrofluoric acid. Boron does not react with air at standard conditions, but it burns at high temperatures to form boron trioxide. Its halides are Lewis acids due to an unfilled valence shell.

Boron-containing compounds can be tested for in solution using curcumin. The normally yellow curcumin reacts with boron, turning deep red. This test will not work in basic conditions, however, as curcumin is normally red in strongly basic solutions.

Physical

Chemically, boron is a metalloid. It is a brown-black solid at standard conditions. It has a very high melting point, 2076 °C and boils at 3927 °C. It's density varies between 2.35 and 2.52 g/cm3.

Boron exists as two main allotrope forms:

  • Amorphous boron: brown powder, similar in aspect with cocoa powder. This one in turn consists of two forms: powder (brown-black) and glassy (opaque black).
  • Crystalline boron: black, extremely hard (about 9.5 on the Mohs scale). It is a poor electrical conductor at room temperature. Crystalline boron also consists of several varieties: α-rhombohedral, α-tetragonal, β-rhombohedral, β-tetragonal. γ-orthorhombic, cubic, high-pressure superconducting and borospherene.[1] Among these, β-rhombohedral is the most thermodynamically stable allotrope.

Availability

Both amorphous and crystalline boron can be bought online. Metallium sells both types, sealed in glass ampoules.

Preparation

Elemental boron can be extracted from boric acid, by dehydrating it to boron trioxide and reducing the oxide with magnesium. The resulting mass, more of a slag actually is treated with hydrochloric acid to remove the impurities. This part should be done slowly, as the residual magnesium diboride reacts with HCl to release borane and diborane that are very toxic and can be pyrophoric in moist air. Once the reaction has stopped, filter the black boron powder and dry it.[2]

Projects

  • Make boranes and organoboron compounds
  • Boron halides

Handling

Safety

Elemental boron, boron oxide, boric acid, borates, and certain organoboron compounds are non-toxic to humans and animals, but are toxic for insects. Boron halides are corrosive.

Storage

No special storage is required.

Disposal

Boron poses little toxicity to the environment and can be dumped in the trash.

References

  1. ↑ http://en.wikipedia.org/wiki/Allotropes_of_boron
  2. ↑ http://www.youtube.com/watch?v=0QBCyOrjR2o

Relevant Sciencemadness threads

Retrieved from "https://www.sciencemadness.org/smwiki/index.php?title=Boron&oldid=7731"