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Student%20Notes%20CHM115-F09-Lecture%2028

Student%20Notes%20CHM115-F09-Lecture%2028 - CHM 115 Lecture...

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1 1 CHM 115 Lecture 28 Today’s Lecture Reading was KTT: The Chemistry of Modern Materials pp. 656-669 Solids & Energy Conduction Band Theory Semiconductors Diodes Solar Energy Next Lecture Reading on Blackboard
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3 This Week in Chemistry Lab: Check out GO , the failure to check out fee is $45 Homework #14 due Friday 12/11 at 6:00 PM Final, Tuesday 12/15, 8:00 AM Hall of Music 2 hours, 40 multiple choice questions Same drill for equipment and seats ! CoursEval 3.0: Please complete by 12/13
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4 4 Study Session If you think I can be of help in preparing for the final exam: Study/Help Session Sunday, 13 December 1:00 to 3:00 PM Room 1105, Lilly Life Sciences Building
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5 Superconducting Ceramics Superconductivity is a phenomenon in which the electrical resistivity of a material drops to nearly zero at some low temperature This is the “critical temperature”, written T c Some metals and metal alloys exhibit superconductivity at T c near 0-20K! (very inconvenient temperatures to work at) Some ceramics have T c around 100K ( much nicer) Complex formulas. Examples: – YBa 2 Cu 3 O 7 with T c = 92K – HgBa 2 Ca 2 Cu 2 O 3 with T c = 153 K demo
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6 Superconducting Ceramics Lattice of a YBa 2 Cu 3 O 7 superconductor
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7 Conduction in Solids Solid classification using conduction :
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8 How does electrical conduction occur in solids? Has to do with ________________________. Energy bands result when _______________ of atoms combine to form a ______________. The spacing between the filled (“valence” and unfilled (“conduction”) bands is the _______________________________________ – The size of E g will determine the properties of the material.
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9 Band Theory Recall atomic energy levels and orbitals Recall: “valence orbitals” = outermost orbital with highest n value
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10 Band Theory As the number of atoms in a solid increases, the number of available energy levels increases. The number of energy levels in a cluster of atoms = the total number available from the individual atoms (for Li 2s orbitals; 1 valence electron each Li atom)
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Band Theory As the number of atoms in the group increases, the energy levels get closer and closer together, until they eventually make a continuous “band.” Electrons will fill energy levels from the bottom up, ___________________________________.
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