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Previously in Chem 104: examples of molecular solids Born Haber Cycles “why doesn’t that solid exist” phase diagra

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!. Big Idea 1.

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Previously in Chem 104: examples of molecular solids Born Haber Cycles “why doesn’t that solid exist” phase diagra

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  1. 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!

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

  3. 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

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

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

  6. Make a mole of a metal M: Energy 6.022 x 1023 MO.’s:a Band of AntiBonding MO’s 6.022 x 1023 Ma.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

  7. 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

  8. 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

  9. ~0 Band Gap Allows Electronic Movement  makes Metal a Conductor Energy AntiBonding Band of a Metal is Empty Conduction Band e- e- e- e- e- e- e- e- Band Gap ~ 0 eV e- e- e- e- Bonding Band of a Metal is e- filled Valence Band

  10. 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

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

  12. Big Idea 3. Impurities Create New Possibilties

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

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

  15. Combining a P-type and N-type Semiconductors Makes a Diode N-type P-type e- e- e- e- Current  this way only

  16. 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-

  17. 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+)

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

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

  20. Big Idea 4. Ceramics go beyond Dirt

  21. Ceramics: The Traditional View Ceramics: can mean many 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

  22. 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

  23. 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

  24. 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

  25. 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?

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