L5 Structures II actual

L5 Structures II actual - interstices formed in...

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Crystalline and Non-Crystalline Structures Lecture 5 October 8, 2009
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Atomic Density Number of atoms per volume Calculate atomic density for the three cubic structures
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Density Mass per volume The unit cell can be repeated to form the entire structure, so the density of the unit cell is the same as the density of the entire solid. V m = ρ
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Atomic Packing Factors*** Note: I had this written incorrectly in the last lecture. Volume of atoms per total volume Calculate APF for the three cubic structures
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Density of Cr (7.19 g/cm 3 ) r(Cr) = 0.125 nm Cr = 52.00 amu What else do we need to know?
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Ionic Solids Charge neutrality is maintained in the crystal Maximize number of NN Ions are not all the same size! Anions tend to be larger than cations (why?)
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Callister
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Close Packed Planes Interstices: The spaces between the atoms Octahedral Tetrahedral In some ionic structures, the cations fit in
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Unformatted text preview: interstices formed in close-packed anion planes Callister Callister NaCl has an FCC structure with 1 Na + and 1 Cl- ion per lattice site. Calculate the theoretical density of NaCl r(Na + ) = 0.102 nm r(Cl-) = 0.181 nm Callister Draw Axes & Write down positions Of the ions Callister Stability of cations in anion interstices Radius Ratio Rules Callister Callister Example: SiO 2 What is the coordination number of Si 4+ in SiO 2 ? What is the CN of O 2-? Example: SiO 2 What is the coordination number of Si 4+ in SiO 2 ? What is the CN of O 2-? First, check to see whether SiO2 is ionic or not O has an electronegativity of 3.5 Si has an electronegativity of 1.8 What is the difference in electronegativity? 1.7 This means that Si-O bonds are about 50% ionic, and 50% covalent. f12_09_pg426 Callister Callister Callister Callister...
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This note was uploaded on 11/28/2010 for the course MTE 209 taught by Professor Tanyafalten during the Fall '09 term at Cal Poly Pomona.

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L5 Structures II actual - interstices formed in...

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