Lect3 Tinh thể

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  • 1. Solids crystalline amorphous well defined structures no orderly structure glass quartz SiO 2 crystal lattice system of points describes arrangement of particles
  • 2. unit cell repeating structural unit lattice 7 unit cells simple cubic formed from packing spheres
  • 3. unit cells crystalline solids hexagonal closest packing “ abab” layers “ abca” layers cubic packing “ aaa” layers in 3 dimensions hexagonal closest pack cubic closest pack “ abab” layers simple cubic body centered cubic
  • 4. Three-Dimensional Cubic Lattices Simple cubic Face-centered cubic Body-centered cubic 1/8 x 8 = 1 particle (1/8 ) x 8 + 1 = 2 particles (1/8 ) x 8 (1/2 ) x 6 + = 4 particles cubic closest pack a a a a b a b a b c a b c coordination number = 6 coordination number = 8 coordination number = 12
  • 5. Calculation of atomic radii Cu faced-centered cubic density = 8.92 g/cm 3 mass = 63.546 g/mol 63.546 g mol 1 mol 6.022 x 10 23 atoms 4 atoms unit cell 8.92 g cm 3 4.732 x 10 -23 cm 3 / unit cell ( ) 1/3 = 3.617 x 10 -8 cm (3.617 x 10 -8 ) 2 + (3.617 x 10 -8 ) 2 = (4r) 2 r = 1.279 x 10 -8 cm 1 cm 1 x 10 -2 m 1 x 10 -12 m 1 pm = 127 pm r+2r+r lattice parameter , a
  • 6. X-Ray Diffraction by Crystals Bragg Equation n  = 2d sin  diffraction interference between waves caused by object in their path constructive or destructive  d
  • 7. Types of Crystalline Solids Covalent Ionic Molecular atoms in lattice ions in lattice molecules in lattice m . p . depends on bonding forces C diamond 3550 o C NaCl 800 O C H 2 O 0 o C covalent ionic H-bonding
  • 8. Covalent solids atoms in lattice carbon sp 3 sp 2 sp 2 hardest material known conduct electricity -  e - diamond doesn’t conduct electricity graphite buckminsterfullerene
  • 9. Covalent solids atoms in lattice metals every lattice point - atom of 1 metal body-centered cubic face-centered cubic hexagonal close packed brass substitutional alloy steel interstitial alloy share valence e - e - “sea” melting point Na 97 o C Cr 1890 o C good conductors
  • 10. Ionic Solids trigonal hole tetrahedral hole octahedral hole too small r = 0.225 R r = 0.414 R composed of charged species – anions and cations each unit cell - anions at lattice points cations in “holes” NaCl face-centered cubic CsCl simple cubic unit cell neutral stoichiometry of compound different in size
  • 11.  
  • 12. Molecular Solids molecules in lattice hemoglobin reaction center 1988 1962 Perutz and Kendrew Deisenhofer, Huber and Michel