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CHEM 201 - 11.5.07

CHEM 201 - 11.5.07 - Packing arrangement in crystals o...

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CHEM 201 – November 5, 2007 Boiling Point – Temperature at which the P vaporization = P surface Normal Boiling Point – Temperature at which the P vaporization = P atm = 1 atm o If the p < 1 atm, then the bp < bp normal Solids o Amorphous solids – that have randomly arranged particles in their structures; no ordered long-range structure o Crystalline solids – ordered long range structure Ionic – made of ions, Ion-Ion forces, very hard and brittle, very high melting point Molecular – made of molecules, held together with van der Waals forces, soft, low melting point Covalent Network – giant 3D network, hard, high melting point Metallic – like a cpvalent network but made of metal atoms
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Unformatted text preview: Packing arrangement in crystals o Atoms are treated as spheres and the pack together to maximize the attractions o Simple cubic – spheres in one layer are on top of spheres in the previous layer, all layers are identical o Coordination number – number of nearest neighbors o Body centered cubic – a-b-a-b arrangement, simple cubic with a layer in between in the holes o Hexagonal close packed – non-cubic unit cell, hexagonal arrangement, spheres in layer b fit in the triangular depressions in layer a, coordination number – 12 o Cubic Close Packed – a-b-c-a-b-c, a-b layers are identical to HCP, third layer is offset from the other two...
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