Previously in Chem 104: Born Haber Cycles “why doesn’t that solid exist” phase diagrams OFFICE HOURS Wed 1-4PM TH 12-2PM & by appointment

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!*

Big Idea 1. Metals have Bonding “Bands”

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

Make a little more complex:

2 a.o.’s

2 bonding MO’s

2 antibonding MO’sEnergy

2 a.o.’s

Make a lot more complex:

20 a.o.’s

20 bonding MO’s

20 antibonding MO’sEnergy

20 a.o.’s

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

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

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

~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-

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”

~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)

Big Idea 3. Impurities Create New Possibilties

~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)

~Impurities Decrease Band Gap makes a Better Semiconductor

Energy

ConductionBand

ValenceBand

Ge

Ge

Ge

As doped –an n-type

semiconductor

e- e-

Combining a P-type and N-type SemiconductorsMakes a Diode

N-type

e- e-

e-

P-type

e-

Current this way only

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

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+)

Ruby

Gem-quality corundum Al2O3 with ~3% Cr(3+) replacing Al(3+)

Al2O3Corundum

Al(3+): CN=6, OhO(2-): CN=4, Td

Nothing recognizable here..

Big Idea 4. Ceramics go beyond Dirt

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

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

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

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

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?