Previously in Chem 104: examples of molecular solids Born Haber Cycles “why doesn’t that solid exist” phase diagrams TODAY Interchapter of Modern Materials Band Theory and some Big Ideas in the chapter Friday – 14.1, 14.2 & bring your questions for Recitation!

Metals have Bonding “Bands” Big Idea 1. Metals have Bonding “Bands”

How Band Theory Evolves from Molecular Orbital Theory Recall the most basic view of MOT Energy antibonding orbital atomic orbital, Like 1s atomic orbital, Like 1s bonding orbital

Make a little more complex: Energy 2 antibonding MO’s 2 a.o.’s 2 a.o.’s 2 bonding MO’s

Make a lot more complex: Energy 20 antibonding MO’s 20 a.o.’s 20 a.o.’s 20 bonding MO’s

Make a mole of a metal M: Energy 6.022 x 1023 MO.’s: a Band of Bonding MO’s 6.022 x 1023 MO.’s: a Band of AntiBonding MO’s 6.022 x 1023 M a.o.’s: make a Band of many, many closely spaced Atomic orbitals 6.022 x 1023 a.o.’s

The Type of Element Determines Band Gap, Band Gap = the energy separation between Bonding and Antibonding Bands Energy AntiBonding Band Of a Metal Band Gap ~ 0 eV Bonding Band Of a Metal

The Type of Element Determines Band Gap Energy AntiBonding Band Of a Metal AntiBonding Band Of a Network Solid Band Gap is Large Band Gap ~ 0 eV Bonding Band Of a Metal Bonding Band Of a Network Solid

~0 Band Gap Allows Electronic Movement  makes Metal a Conductor Energy AntiBonding Band of a Metal is Empty Conduction Band Valence e- e- e- e- e- Band Gap ~ 0 eV e- e- e- e- Bonding Band of a Metal is e- filled

Large Band Gap Prevents Electronic Movement  makes Metal an Insulator Energy Conduction Band at High Energy Band Gap is Too Large for Electrons to “jump” Valence Band At Low Energy

~Small Band Gap Allows Electronic Movement if Energy added  makes a Semiconductor Energy Conduction Band e- by E = Light: Solar Cells e- Band Gap overcome e- by E = Heat: Thermisters (heat regulators) Valence Band

Big Idea 3. Impurities Create New Possibilties

~Impurities Decrease Band Gap  makes a Better Semiconductor Energy Conduction Band Ge Ga doped – a p-type semiconductor e- Ge Valence Band Ge

~Impurities Decrease Band Gap  makes a Better Semiconductor Energy Conduction Band Ge As doped – an n-type semiconductor e- e- Ge Valence Band Ge

Combining a P-type and N-type Semiconductors Makes a Diode 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 P-type e- e- e-

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+)

Al2O3 Corundum Al(3+): CN=6, Oh O(2-): CN=4, Td Nothing recognizable here..

Ceramics go beyond Dirt Big Idea 4. Ceramics go beyond Dirt

Ceramics: can mean many things Ceramics: The Traditional View Make from ground up rocks (“dirt”) Composition: MAlxSiyOz.H2O from silicate and aluminosilicate minerals Begin “Plastic” (workable, malleable) when mixed with water HEAT 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 stability chemically inert

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 From “common” clay; Fired at higher temp From flint + feldspar clays; Fired at highest temp; more vitreous Most translucent, most vitreous, most white, most pure Clay (kaolin) from China: Al2O3.2SiO2.2H2O . “Bone China” originally made from calcined bone, CaO The ‘ring’ test… Firing process: evaporates remaining water away and initiates vitrification

What goes on top of Ceramics Is ceramic too — Glazes Composition similar: silicates + flint + feldspar (SiO2 + SiAlO3) + “flux” (K2O, ZnO, BaCO3 Structure: vitreous Color from Transition Metal minerals/salts added Fe(3+) – red-brown Cu(2+) – turquoise blue and green Co(2+) – “cobalt” blue Ni(2+) – green, brown Mn(2+) –purple, brown

Ceramics: the Modern View Advanced Ceramics or Materials: silicon carbides SiC and nitrides Si3N composites: SiC/Al2O3 “whiskers” Improved Properties: tougher, higher temperatures, fewer defects Examples from Dr. Lukacs golf heads Machine parts tiles All common stuff

Better materials for Solar cells Biggest Idea 5. New Materials are Hot Snazzy graphite relatives: fullerenes, carbon nantubes drug delivery?? electronics? Better materials for Solar cells Biomineralization: how does it grow like that? Superconducting solids Molecular Magnets Artificial bone?