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Midterm 3 - Study Guide

# Midterm 3 - Study Guide - Exam 3 Study Guide Solid State A...

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Exam 3 Study Guide Solid State: A. Become intimately familiar with the summary sheet that was handed out with the ss workbook in class i.e. coordination no., packing style, packing efficiency, edge length in terms of r, net atoms/unit cell for all cubic unit cells we studied: scc, bcc, fcc. B. Know the two broad categories of problems associated with ss: stoichiometry from a z-diagram and calculating radius from density and vice versa. C. Be able to draw z-diagrams from written descriptions of unit cell D. Be able to calculate charge of ions from z-diagrams E. Know atom contributions to unit cells: corner= 1/8; edge= 1/4; face= ½; central= 1 F. Properties of metals: malleable, ductile, conductors of heat and electricity, shiny, high mp’s G. Review ss lab Band Gap/Conductivity: A. The molecular orbital basis for bands in band gap theory. Combining 2 atoms to form a bond involves addition of atom’s wavefunction, these can combine constructively (bonding MO-lower energy) or destructively (antibonding MO-higher energy). Each atom’s electrons fill MO in from low high energy meaning for metals (species with few electrons) only the bonding MO’s are filled leaving empty higher energy antibonding MO’s. The more atoms combining, the more MO’s result (2 atoms lead to 2 MO’s, 1 mole of atoms lead to 1 mole of MO’s and this continuum of MO’s are the bands of band gap theory) B. Generally a filled or partially filled band or valence band and empty higher energy band-conduction band C. Band gap- energetic gap between conduction and valence bands D. Conductors- no band gap; current flows with small amount of applied voltage; conductivity decreases with increasing temperature as atomic vibrational motion increases obstructing electron flow E. Semiconductors- small band gap (< 3 eV) so that modest amounts of energy can give e in the the valence band enough energy to cross band gap into conduction band; increasing temp. increases conductivity

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Midterm 3 - Study Guide - Exam 3 Study Guide Solid State A...

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