09-11 - σ bonds Strong σ bonds localizes the e-s...

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E45 Lecture 11/6/09
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E=0 CB VB E g Semiconductor vs Insulator E g ≈ 1-2eV => semiconductor E g ≈ ≥ 3eV => insulator
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In polymers : Strong covalent bonds along the chain and weak, van der Waals bonds between chains Intermolecular charge transfer is weak but because chains are long, not much intermolecular charge transfer is required Therefore, focus on intramolecular charge transfer
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Polymer with saturated chemical structure, e.g., polyethylene Tetrahedral arrangement of a.o.s sp 3 hybridization C: 1s 2 2s 2 2p 2 Sp 3 hybridization: 2s 1 p x p y p z
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Polymer with saturated chemical structure, e.g., polyethylene Tetrahedral arrangement of a.o.s sp 3 hybridization C: 1s 2 2s 2 2p 2 Sp 3 hybridization: 2s 1 p x p y p z Tetrahedral bonds: Ethane: C 2 H 6 Diamond Polyethylene zig/zag
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Polymer with saturated chemical structure, e.g., polyethylene Tetrahedral arrangement of a.o.s sp 3 hybridization C: 1s 2 2s 2 2p 2 Sp 3 hybridization: 2s 1 p x p y p z Tetrahedral bonds: Ethane: C 2 H 6 Diamond Polyethylene zig/zag All available e - s are tied up in strong covalent
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Unformatted text preview: σ bonds Strong σ bonds localizes the e-s producing and insulator Conjugated polymers (polyacetylene) have unsaturated carbon sp 2 hybridization: sp 2 hybridization: planar σ bonds 120° apart p z orbital is perpendicular to plane e-in p z forms a π bond with neighboring atom’s p z π-bond is parallel to underlying σ bond Resulting in double bond as in Ethylene C 2 H 4 Conjugated polymers (polyacetylene) have unsaturated carbon sp 2 hybridization: sp 2 hybridization: planar σ bonds 120° apart p z orbital is perpendicular to plane π-bond- e-are less strongly bound than σ bond e-. σ => π e-are more easily removed σ => conduction Polymer with saturated chemical structure, e.g., polyethylene Tetrahedral arrangement of a.o.s sp 3 hybridization C: 1s 2 2s 2 2p 2 Sp 3 hybridization: 2s 1 p x p y p z Ethane C 2 H 6 Polyethylene - zig-zag...
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This note was uploaded on 07/05/2010 for the course E 45 taught by Professor Gronsky during the Fall '08 term at Berkeley.

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09-11 - σ bonds Strong σ bonds localizes the e-s...

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