Solids Chem 1C

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Solids Chem 1C
2014-11-24 22:46:56
Chem 1C

Solids Chem 1C
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  1. Ionic solids
    Network of positively and negatively charged ions forming a net neutral solid
  2. Ionic solid held together by and characteristics
    • Electrostatic forces (ionic bonding)
    • Brittle, high melting point
  3. Molecular Solid
    Molecules held together by intermolecular forces
  4. Molecular solid intramolecular vs. intermolecular forces
    Strong forces within molecules and relatively weak intermolecular forces between molecules
  5. Atomic Solids
    Solid made entirely of one element
  6. Type of bond in atomic solid
  7. Allotrope
    Different crystal structures of same atom in solid form
  8. Metallic Solids
    Cations in a sea of electrons
  9. Metallic Solid characteristic
    Strong but malleable, good electrical conductors
  10. Lattice
    Atoms arranged in particular, regular array
  11. Hexagonal Closet Packing
    • -Spheres packed as close as possible
    • -Second layer atoms sit in indentation of 1st layer
    • -ABABAB
  12. Unit Cell
    Smallest repeating unit of a lattice. Repeats in 3D
  13. Cubic Closet Packing
    • -Second layer atoms sit in indentation of first layer
    • -Third layer atoms are above indentations in 1st layer not covered by 2nd layer
    • -ABCABC
  14. Fully within unit cell
    Centered on face
    Centered on edge
    Centered on corner
    • 1 atom
    • 1/2 atom
    • 1/4 atom
    • 1/8 atom
  15. Body-Centered Cubic Packing
    • -Not closest packed
    • -Atoms centered at each corner with one atom centered in the middle of the body of the cell
    • -2 atoms per cell
  16. Simple Cubic Packing
    • -Not closest packed
    • -Spheres packed directly on top of each other
    • -1 atom per unit cell
  17. Simple cubic atoms in cell, neighbors, % occupation
    1 atom, 6 neighbors, 52.4% occupation
  18. Body-Centered Cubic atoms in cell, neighbors, % occupation
    2 atoms, 8 neighbors, 68.0% occupation
  19. Face centered cubic atoms in cell, neighbors, % occupation
    4, 12, 74.0% occupation
  20. Hexagonal number of atoms in cell, neighbors, % occupation
    2 atoms, 12 neighbors, 74.0% occupation
  21. Holes
    • -Close packing of cations and anions
    • -Overall net charge must be 0
  22. Holes: Larger Ions
    • -Anions
    • -Define type of packing
  23. Holes: Smaller Ions
    • -cations
    • -fit into "holes" between large atoms
  24. Tetrahedral Holes
    • -8 holes in unit cell
    • -All 8 fully inside cell
  25. Octahedral Holes
    • -4 holes in unit cell
    • -1 completely inside +12 on edge
  26. Trigonal Holes
    Very small, generally not occupied
  27. Sizes of holes
  28. What determines which holes get filled?
    Ratio of cation radius to anion radius
  29. Tetrahedral hole radius ratio
  30. Octahedral Hole radius ratio
  31. How do anions accommodate cations
    Move slightly apart to accommodate space taken by cations
  32. Band Model
    • Explains the "sea of electrons"
    • -Results in filled orbitals close in energy to empty orbitals
    • -Electrons now are highly mobile
  33. Alloys typically form between
    Electropositive metals that have similar electronegatives
  34. Solid alloy solutions may be
    Substitutional or interstitial
  35. What can you do to a semiconductor to enhance conductivity
  36. n-type semiconductor
    foreign atom with an excess of electrons is added to a pure semi-conductor
  37. p-type semiconductor
    foreign atoms with less electrons are added to a pure semiconductor