Book Notes- Crystal Structure

Book Notes- Crystal Structure - CrystalStructure...

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Crystal Structure Controls of Crystal Structure Structure Controls with Metallic Bonding o Low and nearly = electronegativity o Pack to minimize void space o Lay in layers o Hexagonal closest packing Layers alternate ABAB, parallel to {1,1,1} o Cubic closest packing Every 3 rd  layer aligned ABCABC, parallel to {1,1,1} o Alloys- interchangeable (gold, silver) o Body centered cubic packing Atoms at nodes of body centered cubic lattice Structure Controls  o Strong, hard, high melting points o Specific orientations so orbital’s overlap o Not very close packing Structure Controls with Molecular Crystals o Packed in systematic way o Internal covalent bond, no residual charge or valence to bond
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o Structure Controls with Iconic Bonding o Rule 1- The Coordination Principle Polyhedron of anions around cation # of an coordinating w/ cat determined by relative size of cat and  anion coordination #- #of anions in contact w/ cation Radius Ratio= Rcat/ Ran 12 fold RR~1 Cubic and hexagonal closest packing 8 fold RR<1 Cubic coordination 6 fold RR<.732 Form corners of octahedron- octahedral coor. Cat in center of 4 an and 1 an on bottom and top 4 fold RR<.414 Tetrahedral coordination
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Angle of 109.47 between legs 3 fold RR<.225 Triangular coordination 2 fold RR<.155 Other Coordinating Geometries Some have wrong # of anions Substantially covalent and give direction Coordination of Common Cations O2- most abundant anion Some cations fit multiple coordination’s o Rule 2- Electrostatic Valency Principle Total strength of valency bonds that reach anion from all near 
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This note was uploaded on 09/26/2010 for the course GEO 416k taught by Professor Staff during the Fall '08 term at University of Texas at Austin.

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Book Notes- Crystal Structure - CrystalStructure...

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