intermolecular forces/ structure

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Anonymous
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81197
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intermolecular forces/ structure
Updated:
2011-04-22 20:53:55
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intermolecular
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intermolecular attractions/ structure
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  1. Surface Tension
    the amount of energy required to stretch or increase the surface of a liquid by a unit area, i.e. by 1 cm3
  2. cohesion
    intermolecular attraction by like molecules
  3. adhesion
    an attraction between unlike molecules
  4. viscosity
    a measure of fluids resistance to flow. The viscosity decreases as the temperature increases. Liquids with strong intermolecular forces have higher viscosities than those that have weak intermolecular forces.
  5. The structures and property of water
    its solid form is less dense than its liquid form. Intermolecular hydrogen bonds give water a high specific heat. Water can give off much heat without a change in its temperature and also take in a lot of heat with only a slight rise in temperature for this reason. Each oxygen can form 2 hydrogen bonds thus water- an extremely three dimensional network- each oxygen is approximately tetrahedrally bonded to four hydrogen atoms.
  6. crystalline solid
    possesses rigid and long range order- its atoms, molecules, or ions occupy specific positions
  7. Unit cell
    a basic, repeating structural unit of a crystalline solid
  8. coordination number
    the number of atoms (or ions) surrounding an atom (or ion) in a crystal lattice. Its value tells us how tightly the spheres are packed.- the larger the coordination number, the closer the spheres are to each other.
  9. simple cubic cell
    the basic, repeating unity in the array of spheres. Has 1 whole atom contained within its shared parts.

    a= 2r

    edge length= 2* radius

    this relationship can be used to determine the atomic radius r and the edge length a of a simple cubic cell
  10. body centered cubic unit cell
    the coordination number of each sphere in this structure is 8 (each sphere is in contact with with four spheres in the layer above and four spheres in the layer below). Contains the equivalent of two spheres/atoms per unit cell. Alkali metals all BCC, Cr, Mn, Fe are all BCC.

    a= 4r/ square root of 3

    this relationship can be used to determine the atomic radius r and the edge length a of a body centered cubic cell
  11. face centered cubic
    Has the equivalent of 4 atoms per unit cell. Has a coordination number of 12

    a= square root of 8*r

    this relationship can be used to determine the atomic radius r and the edge length a of a face centered cubic cell
  12. Hexagonal closet packing
    Noble gases are a good example. Have a coordination number of 12.
  13. Ionic crystals
    are composed of charged species and anions and cations are quite different in size. Most have high melting points. Non conductive in solid state. electrostatic attractive forces- hard, brittle, high MP
  14. Covalent crystals
    atoms held together by 3 dimensional network of covalent bonds. Well known are the two allotropes of carbon- diamond (sp3 hybridized) and graphite (sp2 hybridized). Hard, high MP, poor conductor of heat and electricity
  15. molecular crystals
    the lattice point are occupied by molecules and the attractive forces between them are dispersion forces, dipole-dipole attraction and/or hydrogen bonding. Soft, low MP, poor conductor of heat and electricity
  16. Mettalic crystals
    in a sense the simplest- every lattice point in a crystal is occupied by an atoms of the same metal. Are generally BCC, FCC or HCP- consequently they are very dense. in metallic bonding the bonding electrons are delocalized over then entire crystal. Good conductors of heat and electricity.- an array of positive ions in a sea of valence electrons. Soft to hard, low to high MP, good conductor of heat and electricity.
  17. Amorphous solids
    lack a regular three dimensional arrangement of atoms i.e. glass.

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