Previously in Chem 104: Born Haber Cycles “why doesn’t that solid exist” phase diagrams...
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Previously in Chem 104:
• Born Haber Cycles
• “why doesn’t that solid exist”
• phase diagrams
• OFFICE HOURSWed 1-4PMTH 12-2PM& by appointment
TODAY
• Interchapter of Modern Materials
• Band Theory
• and some Big Ideas in the chapter
• Friday –14.1, 14.2 *email me your questions for Recitation!*
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Big Idea 1. Metals have Bonding “Bands”
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How Band Theory Evolves from Molecular Orbital TheoryRecall the most basic view of MOT
atomic orbital, Like 1s
atomic orbital, Like 1s
bonding orbital
antibonding orbitalEnergy
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Make a little more complex:
2 a.o.’s
2 bonding MO’s
2 antibonding MO’sEnergy
2 a.o.’s
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Make a lot more complex:
20 a.o.’s
20 bonding MO’s
20 antibonding MO’sEnergy
20 a.o.’s
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Make a mole of a metal M:
6.022 x 1023 M a.o.’s:
Energy
6.022 x 1023 a.o.’smake a Bandof many, manyclosely spaced Atomic orbitals
6.022 x 1023 MO.’s:a Band of Bonding MO’s
6.022 x 1023 MO.’s:a Band of AntiBonding MO’s
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The Type of Element Determines Band Gap,Band Gap = the energy separation between Bonding
and Antibonding BandsEnergy
AntiBonding BandOf aMetal
Bonding BandOf aMetal
Band Gap ~ 0 eV
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The Type of Element Determines Band Gap
EnergyAntiBonding BandOf aMetal
Bonding BandOf aMetal
Band Gap ~ 0 eV
AntiBonding BandOf aNetwork Solid
Bonding BandOf aNetwork Solid
Band Gap is Large
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~0 Band Gap Allows Electronic Movement makes Metal a Conductor
EnergyAntiBonding Bandof aMetalis Empty
Bonding Bandof aMetalis e- filled
Band Gap ~ 0 eV
ConductionBand
ValenceBand
e-e-e- e-e-e-e- e-e-e-e- e-
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Large Band Gap Prevents Electronic Movement makes Metal an Insulator
Energy
Conduction Bandat High Energy
Valence BandAt Low Energy
Band Gap is Too Largefor Electrons to “jump”
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~Small Band Gap Allows Electronic Movement if Energy added makes a Semiconductor
Energy
Band Gap overcome
ConductionBand
ValenceBand
e-
e-e-
by E = Light: Solar Cells
by E = Heat: Thermisters(heat regulators)
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Big Idea 3. Impurities Create New Possibilties
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~Impurities Decrease Band Gap makes a Better Semiconductor
Energy
ConductionBand
ValenceBand
Ge
Ge
Ge
Ga doped Ge –is a
p-typesemiconductor
e-
Ga orbitals (empty)
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~Impurities Decrease Band Gap makes a Better Semiconductor
Energy
ConductionBand
ValenceBand
Ge
Ge
Ge
As doped –an n-type
semiconductor
e- e-
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Combining a P-type and N-type SemiconductorsMakes a Diode
N-type
e- e-
e-
P-type
e-
Current this way only
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A Diode made of the right materials causes DE loss to be converted to Light: Light Emitting Diode (LED)
N-type
e- e-
e-
P-type
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The funny thing about corundum is, when you have it in a clean single crystal, you get something much different.
Sapphire is Gem-quality corundum Al2O3 with Ti(4+) & Fe(2+) replacing Al(3+)
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Ruby
Gem-quality corundum Al2O3 with ~3% Cr(3+) replacing Al(3+)
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Al2O3Corundum
Al(3+): CN=6, OhO(2-): CN=4, Td
Nothing recognizable here..
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Big Idea 4. Ceramics go beyond Dirt
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Ceramics: The Traditional ViewMake from ground up rocks (“dirt”)Composition: MAlxSiyOz.H2O
from silicate and aluminosilicate mineralsBegin “Plastic” (workable, malleable) when mixed with waterHEAT causes vitrification (“glassification”)
Structure: Amorphous with polycrystallites or vitreous (glass)
Properties: very high melting points—refractories (furnace linings)brittle (not malleable) high mechanical strength and stabilitychemically inert
Ceramics: can mean many things
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Common example and how they differ: Terra cotta -
Stoneware-
Porcelain -
China –
From “common” clay; red color from FeO iron oxides in “dirt”Fired at lowest temp; not glassy
Most translucent, most vitreous, most white, most pureClay (kaolin) from China: Al2O3.2SiO2.2H2O .“Bone China” originally made from calcined bone, CaOThe ‘ring’ test…
From “common” clay; Fired at higher temp
From flint + feldspar clays; Fired at highest temp; more vitreous
Firing process: evaporates remaining water away and initiates vitrification
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Composition similar: silicates + flint + feldspar(SiO2 + SiAlO3) + “flux” (K2O, ZnO, BaCO3
Structure: vitreous
What goes on top of Ceramics Is ceramic too — Glazes
Color from Transition Metal minerals/salts added
Fe(3+) – red-brownCu(2+) – turquoise blue and greenCo(2+) – “cobalt” blueNi(2+) – green, brownMn(2+) –purple, brown
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Improved Properties:• tougher, higher temperatures, fewer defects
Advanced Ceramics or Materials:• silicon carbides SiC and nitrides Si3N• composites: SiC/Al2O3 “whiskers”
Examples from Dr. Lukacs• golf heads• Machine parts• tilesAll common stuff
Ceramics: the Modern View
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Snazzy graphite relatives: fullerenes, carbon nantubes drug delivery?? electronics?
Biggest Idea 5. New Materials are Hot
Better materials for Solar cells
Superconducting solidsMolecular Magnets
Artificial bone?
Biomineralization: how does it grow like that?