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 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 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 a.o.’s 20 antibonding MO’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 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 6.022 x 1023 MO.’s: a Band of Bonding MO’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 Band Gap ~ 0 eV Bonding Band of a Metal is e- filled Conduction Band e- ee- e- e- ee- e- Valence Band 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 by E = Light: Solar Cells ee- Band Gap overcome 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 orbitals (empty) eValence Band Ge Ge Ga doped Ge – is a ptype ~Impurities Decrease Band Gap makes a Better Semiconductor Energy Conduction Band Ge e- Valence Band Ge As doped – an n-type semiconductor e- Ge Combining a P-type and N-type Semiconductors Makes a Diode N-type e- P-type ee- 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- P-type 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.. Big Idea 4. Ceramics go beyond Dirt Ceramics: can The mean Traditional many View things 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: From “common” clay; red color from Terra cotta - FeO iron oxides in “dirt” Fired at lowest temp; not glassy Stoneware- From “common” clay; Fired at higher temp Porcelain - From flint + feldspar clays; Fired at highest temp; more vitreous China 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 Biggest Idea 5. New Materials are Hot Snazzy graphite relatives: fullerenes, carbon nantubes drug delivery?? electronics? Better materials for Solar cells Superconducting solids Molecular Magnets Biomineralization: how does it grow like that? Artificial bone?