Lect3 Tinh thể

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Lect3 Tinh thể

  1. 1. Solids crystalline amorphous well defined structures no orderly structure glass quartz SiO 2 crystal lattice system of points describes arrangement of particles
  2. 2. unit cell repeating structural unit lattice 7 unit cells simple cubic formed from packing spheres
  3. 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. 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. 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. 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. 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. 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. 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. 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

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