Difference between revisions of "Selenium"

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'''Selenium''' is a chemical element with symbol '''Se''' and atomic number 34.
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{{Infobox element
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<!-- top -->
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|image name=Selenium_-_black.jpg
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|image alt=
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|image size=
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|image name comment=Selenium powder - black
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|image name 2=
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|image alt 2=
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|image size 2=
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|image name 2 comment=
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<!-- General properties -->
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|name=Selenium
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|symbol=Se
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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=Black, red, gray
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|appearance=Black, red, gray solid
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<!-- Periodic table -->
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|above=[[Sulfur|S]]
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|below=[[Tellurium|Te]]
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|left=[[Arsenic]]
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|right=[[Bromine]]
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|number=34
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|atomic mass=78.971(8)
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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=16
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|group ref=
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|group comment=
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|period=4
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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=[Ar] 3d<sup>10</sup> 4s<sup>2</sup> 4p<sup>4</sup>
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|electron configuration ref=
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|electron configuration comment=
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|electrons per shell=
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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, gray, red
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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=494
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|melting point C=221
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|melting point F=430
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|melting point ref=
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|melting point comment=
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|boiling point K=958
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|boiling point C=685
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|boiling point F=1265
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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=4.81
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|density gpcm3nrt ref=
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|density gpcm3nrt comment=(gray)
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|density gpcm3nrt 2=4.39
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|density gpcm3nrt 2 ref=
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|density gpcm3nrt 2 comment=(alpha)
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|density gpcm3nrt 3=4.28
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|density gpcm3nrt 3 ref=
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|density gpcm3nrt 3 comment=(vitreous)
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|density gpcm3mp=3.99
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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=1766
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|critical point MPa=27.2
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|critical point ref=
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|critical point comment=
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|heat fusion=6.69
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|heat fusion ref=
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|heat fusion comment=(gray)
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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=95.48
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|heat vaporization ref=
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|heat vaporization comment=
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|heat capacity=25.363
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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=500
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|vapor pressure 10=552
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|vapor pressure 100=617
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|vapor pressure 1 k=704
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|vapor pressure 10 k=813
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|vapor pressure 100 k=958
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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='''6''', 5, '''4''', 3, '''2''', 1, −1, '''−2'''
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|oxidation states ref=
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|oxidation states comment=(a strongly acidic oxide)
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|electronegativity=2.55
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|electronegativity ref=
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|electronegativity comment=
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|ionization energy 1= 941.0
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|ionization energy 1 ref=
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|ionization energy 1 comment=
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|ionization energy 2=2045
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|ionization energy 2 ref=
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|ionization energy 2 comment=
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|ionization energy 3=2973.7
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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=120
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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=120±4
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|covalent radius ref=
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|covalent radius comment=
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|Van der Waals radius=190
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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=Hexagonal
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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=3350
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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=37
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|thermal expansion ref=
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|thermal expansion comment=(amorphous)
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|thermal expansion at 25=
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|thermal expansion at 25 ref=
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|thermal expansion at 25 comment=
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|thermal conductivity=0.519
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|thermal conductivity ref=
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|thermal conductivity comment=(amorphous)
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|thermal conductivity 2=
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|thermal conductivity 2 ref=
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|thermal conductivity 2 comment=
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|thermal diffusivity=
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|thermal diffusivity ref=
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|thermal diffusivity comment=
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|electrical resistivity=
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|electrical resistivity unit prefix=
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|electrical resistivity ref=
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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=
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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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|Curie point ref=
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|Curie point comment=
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|magnetic ordering=Diamagnetic
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|magnetic ordering ref=
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|magnetic ordering comment=
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|tensile strength=
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|tensile strength ref=
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|tensile strength comment=
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|Young's modulus=10
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|Young's modulus ref=
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|Young's modulus comment=
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|Shear modulus=3.7
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|Shear modulus ref=
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|Shear modulus comment=
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|Bulk modulus=8.3
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|Bulk modulus ref=
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|Bulk modulus comment=
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|Poisson ratio=0.33
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|Poisson ratio ref=
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|Poisson ratio comment=
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|Mohs hardness=2.0
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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=
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|Brinell hardness=736
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|Brinell hardness ref=
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|Brinell hardness comment=
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|CAS number=7782-49-2
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|CAS number ref=
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|CAS number comment=
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<!-- History -->
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|naming=After Selene, Greek goddess of the moon
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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=
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|discovery date ref=
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|discovery date=
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|first isolation by=
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|first isolation date ref=
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|first isolation date=
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|discovery and first isolation by=Jöns Jakob Berzelius and Johann Gottlieb Gahn (1817)
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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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|history comment=
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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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}}
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'''Selenium''' is a chemical element with symbol '''Se''' and atomic number 34. It is widely used in the semiconductor industry.
  
 
==Properties==
 
==Properties==
 
===Chemical===
 
===Chemical===
−
Like sulfur, selenium will burn in the presence of [[oxygen]] to yield selenium dioxide.
+
Like sulfur, selenium will burn in the presence of [[oxygen]] to yield [[selenium dioxide]].
  
 
:Se + O<sub>2</sub> → SeO<sub>2</sub>
 
:Se + O<sub>2</sub> → SeO<sub>2</sub>
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:Se + 4 H<sub>2</sub>O + 3 Cl<sub>2</sub> → H<sub>2</sub>SeO<sub>4</sub> + 6 HCl
 
:Se + 4 H<sub>2</sub>O + 3 Cl<sub>2</sub> → H<sub>2</sub>SeO<sub>4</sub> + 6 HCl
 +
 +
Selenium dissolves in concentrated nitric acid with evolution of oxides of nitrogen:<ref>https://woelen.homescience.net/science/chem/exps/selenium/index.html</ref><ref>https://prepchem.com/synthesis-of-selenium-dioxide</ref>
 +
 +
:4 HNO<sub>3</sub> + Se → H<sub>2</sub>SeO<sub>3</sub> + 4 NO<sub>2</sub> + H<sub>2</sub>O
 +
 +
When selenous acid is reduced with sulfur dioxide or metabisulfite red selenium is formed.
 +
 +
In concentrated sulfuric acid selenium dissolves to give a deep green solution.<ref>Holleman-Wiberg, ''Lehrbuch der anorganischen Chemie'', 102nd ed., page 622f.</ref>
 +
 +
:Se<sub>8</sub> + 3 H<sub>2</sub>SO<sub>4</sub> → Se<sub>8</sub><sup>2+</sup> + 2 HSO<sub>4</sub><sup>-</sup> + SO<sub>2</sub> + 2 H<sub>2</sub>O
 +
 +
Diluting this solution in water forms red selenium.
 +
 +
When selenium is dissolved in hot concentrated sodium or potassium hydroxide, deep red polyselenides form.<ref>http://selenium.atomistry.com/chemical_properties_selenium.html</ref> Polyselenides form less readily than polysulfides. When strongly diluted, polyselenides hydrolyze into red selenium.<ref>Holleman-Wiberg, ''Lehrbuch der anorganischen Chemie'', 102nd ed., page 624</ref>
  
 
===Physical===
 
===Physical===
 
Selenium is a solid nonmetal at standard conditions. It has several allotrope forms:
 
Selenium is a solid nonmetal at standard conditions. It has several allotrope forms:
−
*'''Amorphous''': Has a brick-red color, as is the most common form of selenium obtained from chemical reactions.
+
*'''Amorphous''' or '''red''': Has a brick-red color, as is the most common form of selenium obtained from chemical reactions.
 
*'''Black''': Also known as '''vitreous''' selenium, this form is a dull grey solid, obtained by rapidly melting its amorphous form. The structure of black selenium is irregular and complex, consisting of polymeric rings. It is slightly soluble in [[carbon disulfide]].
 
*'''Black''': Also known as '''vitreous''' selenium, this form is a dull grey solid, obtained by rapidly melting its amorphous form. The structure of black selenium is irregular and complex, consisting of polymeric rings. It is slightly soluble in [[carbon disulfide]].
 
*'''Gray''': Obtained by heating black selenium to 180°C. This is the most dense and stable form of selenium. It is not soluble in carbon disulfide or other organic solvents. Unlike the black variety, its structure is hexagonal crystal lattice consisting of helical polymeric chains. Gray selenium is a semiconductor, that also shows appreciable photoconductivity.
 
*'''Gray''': Obtained by heating black selenium to 180°C. This is the most dense and stable form of selenium. It is not soluble in carbon disulfide or other organic solvents. Unlike the black variety, its structure is hexagonal crystal lattice consisting of helical polymeric chains. Gray selenium is a semiconductor, that also shows appreciable photoconductivity.
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==Availability==
 
==Availability==
 
Selenium is sold by chemical suppliers. It can also be purchased from Ebay and Metallium.
 
Selenium is sold by chemical suppliers. It can also be purchased from Ebay and Metallium.
 +
 +
Native (i.e., elemental) selenium is a rare mineral, which does not usually form good crystals, but, when it does, they are steep rhombohedra or tiny acicular (hair-like) crystals.
  
 
==Preparation==
 
==Preparation==
 
Elemental selenium can be made by reducing selenous acid with sulfur dioxide.
 
Elemental selenium can be made by reducing selenous acid with sulfur dioxide.
 +
 +
The red α, β, and γ forms are produced from solutions of black selenium by varying the evaporation rate of the solvent (usually CS<sub>2</sub>).
  
 
A good tutorial to make selenium allotropes can be found [http://woelen.homescience.net/science/chem/exps/selenium/index.html here].
 
A good tutorial to make selenium allotropes can be found [http://woelen.homescience.net/science/chem/exps/selenium/index.html here].
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*Made cadmium selenide
 
*Made cadmium selenide
 
*Make red glass
 
*Make red glass
 +
*Make red selenium
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*Make the green Se<sub>8</sub><sup>2+</sup>
 +
*Make polyselenides
 +
*Make selenites and selenates
  
 
==Handling==
 
==Handling==
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===Disposal===
 
===Disposal===
 
As selenium is not cheap and not easy to come by, it's best to try to recycle it.
 
As selenium is not cheap and not easy to come by, it's best to try to recycle it.
 +
 +
==Gallery==
 +
<gallery widths="200" position="center" columns="4" orientation="none">
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Red_Selenium.jpg|The red allotrope of selenium
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Selenium_cation.jpg|The green solution of Se<sub>8</sub><sup>2+</sup> obtained from selenium powder in hot concentrated sulfuric acid
 +
Polyselenide.jpg|When selenium is dissolved in hot concentrated sodium hydroxide, a deep red solution of polyselenide forms
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</gallery>
  
 
==References==
 
==References==
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[[Category:Chalcogens]]
 
[[Category:Chalcogens]]
 
[[Category:P-block]]
 
[[Category:P-block]]
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[[Category:Minerals]]

Latest revision as of 10:01, 25 September 2020

Selenium,  34Se
Selenium - black.jpg
Selenium powder - black
General properties
Name, symbol Selenium, Se
Allotropes Black, red, gray
Appearance Black, red, gray solid
Selenium in the periodic table
S
↑
Se
↓
Te
Arsenic ← Selenium → Bromine
Atomic number 34
Standard atomic weight (Ar) 78.971(8)
Group, block , p-block
Period period 4
Electron configuration [Ar] 3d10 4s2 4p4
Physical properties
Black, gray, red
Phase Solid
Melting point 494 K ​(221 °C, ​430 °F)
Boiling point 958 K ​(685 °C, ​1265 °F)
Density near r.t. 4.81 g/cm3 (gray)
4.39 g/cm3 (alpha)
4.28 g/cm3 (vitreous)
when liquid, at  3.99 g/cm3
Critical point 1766 K, 27.2 MPa
Heat of fusion 6.69 kJ/mol (gray)
Heat of 95.48 kJ/mol
Molar heat capacity 25.363 J/(mol·K)
 pressure
Atomic properties
Oxidation states 6, 5, 4, 3, 2, 1, −1, −2 ​(a strongly acidic oxide)
Electronegativity Pauling scale: 2.55
energies 1st: 941.0 kJ/mol
2nd: 2045 kJ/mol
3rd: 2973.7 kJ/mol
Atomic radius empirical: 120 pm
Covalent radius 120±4 pm
Van der Waals radius 190 pm
Miscellanea
Crystal structure ​Hexagonal
Speed of sound thin rod 3350 m/s (at 20 °C)
Thermal expansion 37 µm/(m·K) (amorphous)
Thermal conductivity 0.519 W/(m·K) (amorphous)
Magnetic ordering Diamagnetic
Young's modulus 10 GPa
Shear modulus 3.7 GPa
Bulk modulus 8.3 GPa
Poisson ratio 0.33
Mohs hardness 2.0
Brinell hardness 736 MPa
CAS Registry Number 7782-49-2
History
Naming After Selene, Greek goddess of the moon
Discovery and first isolation Jöns Jakob Berzelius and Johann Gottlieb Gahn (1817)
· references

Selenium is a chemical element with symbol Se and atomic number 34. It is widely used in the semiconductor industry.

Properties

Chemical

Like sulfur, selenium will burn in the presence of oxygen to yield selenium dioxide.

Se + O2 → SeO2

Unlike sulfur dioxide, selenium dioxide is a solid.

Selenium will be oxidized by chlorine in water to give selenic acid and hydrochloric acid.

Se + 4 H2O + 3 Cl2 → H2SeO4 + 6 HCl

Selenium dissolves in concentrated nitric acid with evolution of oxides of nitrogen:[1][2]

4 HNO3 + Se → H2SeO3 + 4 NO2 + H2O

When selenous acid is reduced with sulfur dioxide or metabisulfite red selenium is formed.

In concentrated sulfuric acid selenium dissolves to give a deep green solution.[3]

Se8 + 3 H2SO4 → Se82+ + 2 HSO4- + SO2 + 2 H2O

Diluting this solution in water forms red selenium.

When selenium is dissolved in hot concentrated sodium or potassium hydroxide, deep red polyselenides form.[4] Polyselenides form less readily than polysulfides. When strongly diluted, polyselenides hydrolyze into red selenium.[5]

Physical

Selenium is a solid nonmetal at standard conditions. It has several allotrope forms:

  • Amorphous or red: Has a brick-red color, as is the most common form of selenium obtained from chemical reactions.
  • Black: Also known as vitreous selenium, this form is a dull grey solid, obtained by rapidly melting its amorphous form. The structure of black selenium is irregular and complex, consisting of polymeric rings. It is slightly soluble in carbon disulfide.
  • Gray: Obtained by heating black selenium to 180°C. This is the most dense and stable form of selenium. It is not soluble in carbon disulfide or other organic solvents. Unlike the black variety, its structure is hexagonal crystal lattice consisting of helical polymeric chains. Gray selenium is a semiconductor, that also shows appreciable photoconductivity.

Availability

Selenium is sold by chemical suppliers. It can also be purchased from Ebay and Metallium.

Native (i.e., elemental) selenium is a rare mineral, which does not usually form good crystals, but, when it does, they are steep rhombohedra or tiny acicular (hair-like) crystals.

Preparation

Elemental selenium can be made by reducing selenous acid with sulfur dioxide.

The red α, β, and γ forms are produced from solutions of black selenium by varying the evaporation rate of the solvent (usually CS2).

A good tutorial to make selenium allotropes can be found here.

Projects

  • Selenium halides
  • Made cadmium selenide
  • Make red glass
  • Make red selenium
  • Make the green Se82+
  • Make polyselenides
  • Make selenites and selenates

Handling

Safety

Selenium and most of its compounds tend to be toxic if ingested in high quantities.

Storage

In closed containers.

Disposal

As selenium is not cheap and not easy to come by, it's best to try to recycle it.

Gallery

  • The red allotrope of selenium

  • The green solution of Se82+ obtained from selenium powder in hot concentrated sulfuric acid

  • When selenium is dissolved in hot concentrated sodium hydroxide, a deep red solution of polyselenide forms

References

  1. ↑ https://woelen.homescience.net/science/chem/exps/selenium/index.html
  2. ↑ https://prepchem.com/synthesis-of-selenium-dioxide
  3. ↑ Holleman-Wiberg, Lehrbuch der anorganischen Chemie, 102nd ed., page 622f.
  4. ↑ http://selenium.atomistry.com/chemical_properties_selenium.html
  5. ↑ Holleman-Wiberg, Lehrbuch der anorganischen Chemie, 102nd ed., page 624

Relevant Sciencemadness threads

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