Download (Lecture(21) - MSU Chemistry

Today’s(Topics!Chemistry*of*the*Representative*Elements*II"
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• Overview'of'the'Group'4'Elements'
• Carbon'
• Allotropes'(properties'and'bonding)'
• Types'of'compounds'formed'by'carbon'
• Hybridization'of'carbon'atoms,'!C'and'!Cbond'formation,'geometry'
• Oxidation'numbers'in'carbon'compounds'
• Silicon'
• How'does'bonding'of'Si'differ'from'that'of'C?'
• Silicate'structures'
• Oxidation'numbers'in'silicates'
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Figures'taken'from'Chemistry:+The+Central+Science,'7th'ed.'by'T.'L.'Brown,'H.'E.'LeMay,'Jr.,'B.'E.'Bursten,'
PrenticeCHall,'1997;'Chemistry,'4th'ed.'by'J.'McMurray'and'R.'C.'Fay,'PrenticeCHall,'2004;'and'Chemistry:+
Molecules,+Matter,+and+Change,'3rd'ed.,'by'P.'Atkins'and'L.'Jones,'W.'H.'Freeman,'1997.'
All+materials+are+©+2012–2013+Lynmarie+A.+Posey+and+Michigan+State+University+unless+otherwise+noted;+
all+rights+reserved.+
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Learning(Objectives((Lecture(21)"
You'should:'
1. be'familiar'with'the'properties'of'and'bonding'in'the'different'allotropes'of'carbon.'
2. know'the'different'types'of'compounds'formed'by'carbon'and'be'able'to'classify'
carbon'compounds.'
3. be'able'to'determine'the'oxidation'number'of'C'in'carbon'compounds.'
4. know'the'relationship'between'hybridization'of'carbon'atoms,'the'number'of'σ'and'π'
bonds,'and'bond'geometry.'
5. understand'how'the'bonding'in'Si'differs'from'that'in'C'and'why'Si'is'found'
predominately'bonded'to'oxygen'in'silicates'and'aluminosilicates.'
6. be'able'to'determine'the'charge'on'silicates'based'on'their'structures'and/or'
chemical'formula.'
7. be'prepared'to'determine'the'oxidation'numbers'of'elements'found'in'silicates'and'
aluminosilicates.'
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Group&4:&Carbon&&&Silicon"
Group'4'Elements:'C,'Si,'Ge,'Sn,'Pb'
• nonmetal'(C),'metalloids'(Si,'Ge),'and'metals'(Sn,'Pb)'
• valence'shell'electron'configuration'!" ! !"! '(“electron'perfect")'
Carbon'&'Silicon
• variety'in'types'of'bonding'which'depends'on'bonding'partners'
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Allotropes)of)Carbon"
Diamond"
• sp3Chybridized'carbons,'4'single'bonds,'tetrahedral'
arrangement'of'bonds'
• insulator'and'very'hard'material'
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Graphite
• sp2Chybridized'carbons,'3'σ'and'1'π'bonds.'A'double'bond'
consists'of'a'σ'and'a'π'bond,'while'each'single'bond'consists'of'one'σ'bond'(2'single'
and'1'double'bonds),'trigonal'planar'bonding'geometry'about'each'C'
• sheets'consisting'of'fused'6Cmembered'rings'with'no'
covalent'bonding'between'the'sheets'
• CCC'distances:'1.42'Å'within'layer;'3.35'Å'between'
layers'
• conductor'and'soft'material'
(FiguresCBrown,'LeMay,'&'Bursten)'
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Fullerenes"(C60,"C70,"C76,"C84...)"
• Discovered'by'Smalley,'Kroto,'and'coworkers'in'the'mid'1980’s.'Nobel'Prize'in'1996.'
• sp2Chybridized'carbons'
• 5C'and'6Cmembered'rings'
• found'in'soot'and'other'carbon'deposits;'can'be'produced'by'striking'a'electric'arc'
(discharge)'between'carbon'electrodes'in'an'inert'atmosphere'or'by'blasting'a'
graphite'rod'with'a'laser'in'an'inert'atmosphere'
(Figure-McMurray & Fay)
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Carbon'Compounds'(Carbides)"
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Types"of"Carbon"Compounds"[depends"on"bonding"partner(s)]"
1. Saline'
• with'Group'1'and'2'metals'and'Al'
2. Metallic'
• with'dCblock'(transition'metals)'and'fCblock'(lanthanides'and'actinides)'metals'
3. Metalloid'
• with'B'and'Si'
4. Molecular'
• with'nonmetals'(not'carbides).'Ex.'CS2,'CCl4,'CH4,'CO2'
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Saline"
Ionic'compounds'formed'with'Group'1'and'2'elements'as'well'as'Al'
• Be2C,'Al4C3'(contain'! !! ).'Note'the'diagonal'relationship'between'Be'and'Al.'
• Na2C2'(contains'!!!! )'
• Mg2C3'(contains'!!!! )'
Prepared'by
• combining'elements'at'high'temperature'
• reacting'metal'oxide'with'carbon'at'high'temperature'
• reacting'acetylene'(HC≡CH)'with'metal'in'ammonia'solution'
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Metallic(&(Metalloid"
Metallic"
• interstitial'compounds'with'C'occupying'octahedral'cavities'in'the'metallic'lattice'
• octahedral'cavityC6'nearest'neighbors'making'the'C'hypervalent'(more'than'4'
bonds)'
• strong'metalCcarbon'bonds'result'in'very'hard'material'
• WC'(tungsten'carbide)'
• FeC3'(cementite,'found'in'steel,'particularly'tool'steel)'
Metalloid
• SiC'(two'Group'4'elements)Cdiamond'structure'(tetrahedral'bonding'geometry'for'
each'atom)'with'Si'occupying'half'of'the'sites'
• B12C3'rock'salt'lattice'structure'of'B12'icosahedra'and'C3'chains'covalently'held'
together.'
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Molecular"
Compounds'that'are'the'subject'of'the'field'of'Organic'Chemistry'
sp3'hybridization'
• tetrahedral'bonding'geometry'
• 4'σ'bonds'(4'single'bonds)''
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sp2'hybridization'
• trigonal'planar'bonding'geometry'
• 3'σ'bonds'+'1π'bond'(2'single'bonds'and'1'double'bond)''
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sp'hybridization'
• linear'bonding'geometry'
• 2'σ'bonds'+'2π'bonds'(1'single'bond'and'1'triple'bond'or'2'double'bonds)''
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Silicon'&'Its'Compounds"
The'high'purity'silicon'used'in'the'semiconductor'industry'is'purified'by'distillation'of'
SiCl4,'reaction'with'Mg,'and'zone'refining.'(FigureCMcMurray'&'Fay)'
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Silicates"and"Aluminosilicates"
The'earth’s'crust'is'49.5%'O,'25.7%'Si,'7.5%'Al.'
Silicon'is'generally'found'bonded'to'oxygen'in'silicates'(sand,'quartz)'and'
aluminosilicates.'
Heating'silica'cause'transitions'between'crystalline'forms'and'finally'to'a'glass.'
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!"#°"
!"#$°"
!"!#°"
quartz ⟶ tridymite ⟶ cristobalite ⟶ glass(amorphous!silica, SiO! )'
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Further'heating'transforms'glass'to'amorphous'silicon'
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glass(amorphous!silica, SiO! ) ⟶ amorphous!silicon'
Cristobalite'(structure'similar'to'diamond'except'that'
there'is'an'O'between'every'pair'of'Si'atoms)'
(Figure-Atkins & Jones)
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Si"and"C"are"in"the"same"group."What"makes"Si"different"from"C?"
• larger'
• d'orbitals'available'for'bonding'
• still'electron'perfect/precise'
Comparison"of"bonds:"Si"vs."C
• SiCSi'bonds'(226'kJ'mol–1)'are'weaker'than'CCC'bonds'(356'kJ'mol–1)'
• SiCH'bonds'(323'kJ'mol–1)'are'weaker'than'CCH'bonds'(416'kJ'mol–1)'
• However,'SiCO'bonds'(~452'kJ'mol–1)'are'much'stronger'than'CCO'bonds''
(358'kJ'mol–1)'
Based'on'comparison'of'the'relative'strengths'of'other'bonds'involving'C'and'Si,'one'
might'have'expected'a'SiCO'bond'strength'of'~240'kJ'mol–1.''
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Why'is'the'SiCO'bond'so'strong?'Si'has'valence'shell'd'orbitals'available'to'participate'in'a'
π'bonding'interaction'with'a'p'orbital'in'O.'This'additional'dπCpπ'interaction'leads'to'the'
enhanced'strength'of'the'SiCO'bond.'
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Because'the'SiCO'bond'is'so'much'stronger'than'bonds'formed'by'Si'with'other'elements,'
most'Si'in'nature'is'found'bonded'to'oxygen'in'the'form'of'silicates'and'aluminosilicates.'
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The'compound'SiH4'(silane)'reacts'immediately'to'form'silicates'when'exposed'to'air.'
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Silicates"
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Silicates'are'ionic'compounds'consisting'of'silicon'oxoanions'plus'cations'such'as'Na+,'K+,'
Mg2+,'and/or'Ca2+'to'balance'the'charge.'
Aluminosilicates'(feldspars)'are'silicates'that'contain'Al'in'place'of'some'of'Si'atoms'in'the'
silicon'oxyanions.'
Basic&Building&Block:!!"#!!
! &(FigureCMcMurray'&'Fay)&
Charge'on'the'silicate'is'determined'by'the'number'of'terminal'oxygens:'4!×!−1 = −4'
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Orthosilicates&
Compounds'containing'the'basic'!"#!!! 'building'block'with'a'1:4'SiCtoCO'ratio'
Ex.'zircon'ZrSiO4'and'olivine'(Fe,'Mg)2SiO4'
Pyrosilicate&
Condensation'of'two'!"#!!! 'units'yields'the'pyrosilicate'structure'!"! !!!! 'with'1:3.5'SiCtoC
O'ratio''
Ex.'hardystonite'
Ca2ZnSi2O7'
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(FigureCMcMurray'&'Fay)'
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Metasilicates&
SiCtoCO'ratio'1:3'
Sharing'of'two'O'per'SiO4'tetrahedron'yields'cyclic'anions'or'extended'chain'anions'
Cyclic"Metasilicates"
Ex.'bentonite'BaTiSi3O9'(contains'the'cyclic'!"! !!!! 'metasilicate)'(FigureCMcMurray'&'Fay)'
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beryl'Al2Be3Si6O18'(substitution'of'Cr3+'for'Al3+'yields'emerald,'while'substitution'of'Al3+'
with'Fe2+'yields'blue'aquamarine)'(FiguresCMcMurray'&'Fay)'
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Chain"Metasilicates"
Pyroxenes'(single'chain)''(FiguresCMcMurray'&'Fay)'
Ex.'diopside'CaMgSi2O6'
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Another'example:'enstatite'MgSiO3'or'Mg2Si2O6'
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Amphiboles'(double'chain)'(FiguresCMcMurray'&'Fay)'
'Ex.'tremolite'Ca2Mg5(OH)2(Si4O11)2'(an'asbestos'mineral)'
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Silicate&Sheets&
SiCtoCO'ratio'1:2.5'
Sharing'of'three'O'per'SiO4'tetrahedron'yields'sheet'structure'(FigureCMcMurray'&'Fay)'
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Properties'of'materials'with'silicate'sheet'structure'are'strongly'dependent'on'the'ions'
found'between'the'sheets.'
Talc'Mg3(OH)2Si4O10'
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Mica'K(Mg,'Fe)3(OH)2AlSi3O10'(example'of'aluminosilicate'in'which'one'of'the'Si'atoms'in'
each'Si4O104–'unit'is'replaced'by'an'Al'to'give'AlSi3O105–'subunits)'(PhotoCMcMurray'&'Fay)'
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38Dimensional&Aluminosilicate&Structures&
Start'with'a'SiCtoCO'ratio'1:2'and'then'substitute'Al'for'some'of'the'Si'atoms.''
• When'Al'replaces'Si'in'the'bonding'framework,'it'only'contributes'3'electrons'rather'
than'the'4'contributed'by'Si.'An'additional'electron'is'provided'by'ionization'of'an'
alkali'metal,'such'as'Na'or'K.'A'negative'charge'is'carried'by'the'aluminosilicate'
framework'for'every'Al'substituted'for'Si,'and'the'alkali'metal'ions'then'occupy'
nearby'sites'in'the'aluminosilicate'structure.'
Ex.'feldspars'such'as'albite'Na3AlSi3O8,'ultramarines,'sodalite,'lapis'lazuli''
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Ex.'zeolites,'which'are'used'as'catalysts.'(Notice'the'open'pore'structure.)'
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