chem104alecture23 - Chem 104A, UC, Berkeley Chem 104A, UC,...

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1 Chem 104A, UC, Berkeley Solid State Structure Solid State Structure Reading: Reading: MT Chapter 7 MT Chapter 7 DG Chapter 7 DG Chapter 7 Chem 104A, UC, Berkeley Chem 104A, UC, Berkeley MgB 2 , superconductor, Tc=39 K Chem 104A, UC, Berkeley CaB CaB 6
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2 Chem 104A, UC, Berkeley XeF 2 • large crystals at RT • body-centered tetragonal • strong interactions between XeF 2 molecules (high Δ H sub ) -0.5 F-Xe +1 -F -0.5 • packing structure distances F from equatorial nonbonding electrons on Xe Xe F F Unit cell Zemva, B. Noble Gases: Inorganic Chemistry. In Encyclopedia of Inorganic Chemistry ; King, R. B., Ed.; John Wiley & Sons: New York, 1994; pp 2660-2680. Chem 104A, UC, Berkeley Molecular packing, projection down b axis XeF 4 • square planar in gas phase • nearly square planar as a solid • strong electrostatic interactions between molecules in solid Zemva, B. Noble Gases: Inorganic Chemistry. In Encyclopedia of Inorganic Chemistry ; King, R. B., Ed.; John Wiley & Sons: New York, 1994; pp 2660-2680. Chem 104A, UC, Berkeley KrF 2 z Lowest average bond energy of any fluoride compound. z D h symmetry z Unit Cell z Molecules aligned perp. z Places negatively charged F atoms close to positively charged krypton atoms. Zemva, B. Noble Gases: Inorganic Chemistry. In Encyclopedia of Inorganic Chemistry ; King, R. B., Ed.; John Wiley & Sons: New York, 1994; pp 2660-2680. Chem 104A, UC, Berkeley Sand Æ Silicon Æ Computer Chips
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3 Chem 104A, UC, Berkeley Gemstone Sapphire Garnet Topaz Synthetic ZrO2 Chem 104A, UC, Berkeley ZrO2 Diamond Chem 104A, UC, Berkeley Salt : NaCl Chem 104A, UC, Berkeley Abalone Shell
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4 Chem 104A, UC, Berkeley Crystalline Solids Chem 104A, UC, Berkeley CARBON : Diamond Chem 104A, UC, Berkeley Amorphous Solids Chem 104A, UC, Berkeley Molecular solids Covalent Ionic Metallic
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5 Chem 104A, UC, Berkeley Chem 104A, UC, Berkeley Na + Cl - IE(Na)= 5.14eV EA(Cl) =3.61 eV ?? Why NaCl solid Chem 104A, UC, Berkeley E U 0 r n r c r B r e Z Z E E U + = + = + 0 2 4 πε Ionic Pair 0 ε Permittivity of vacuum Chem 104A, UC, Berkeley 12 Xe, Au+ 10 Kr, Ag+ 9 Ar, Cu+ 7 Ne 5 He n Ion Conf. Born Exponent
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6 Chem 104A, UC, Berkeley 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 Chem 104A, UC, Berkeley Lattice Stabilization Energy: Ions adopt a simple lattice structure that maximize favorable Electrostatic interactions. ...... ) 5 24 4 6 3 8 2 12 6 ( 4 0 2 + + + = + πε e Z Z E lattice c ...... 5 24 4 6 3 8 2 12 6 + + + = NaCl A 74756 . 1 = Chem 104A, UC, Berkeley Structure Type Madelung Constant CsCl 1.763 NaCl 1.748 ZnS ( Wurtzite ) 1.641 ZnS ( Zinc Blende ) 1.638 M& T: p208 Chem 104A, UC, Berkeley For one mole of a crystalline compound: Lattice energy = n r c r NB r e Z NZ A E E U + = + = + 0 2 4 N: Avogadvo’s constant, 6.02e23 E U 0 r
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7 Chem 104A, UC, Berkeley Energy is Minimum when 0 = dr dU n r e Z AZ B r nNB r e Z NZ A n n 0 1 2 1 2 0 2 4 0 4 πε + + + = = ) 1 1 ( 4 0 0 2 0 n r e Z ANZ U = + Born-Lande Equation: Chem 104A, UC, Berkeley 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 o A r 81 . 2 0 = U 0 =-755kJ/mol Chem 104A, UC, Berkeley Born-Haber Cycle: M(g) Æ M+ (g) + X(g) Æ X-(g) M(s) + ½ X2 (g) Æ MX (s) IE H Δ EA H Δ AX H Δ AM H Δ f H Δ 0 U H H H H H EA IE AX AM f + Δ + Δ + Δ + Δ = Δ 0 U Calculated: -381 kJ/mol Experimental: -411 kJ/mol Chem 104A, UC, Berkeley
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This note was uploaded on 04/12/2008 for the course CHEM 104 taught by Professor Yang during the Spring '04 term at University of California, Berkeley.

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chem104alecture23 - Chem 104A, UC, Berkeley Chem 104A, UC,...

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