The positions of the components in a crystalline

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the positions of the components in a crystalline solid are represented by a lattice array amorphous solids- those wih considerabl disorder in their structures x-ray diffraction- determine crystalline structures, when beams of light are scattered  froma  regular array of points or lines where spacings between the components are  comparable to the wavelength of the light simple cubic 1 atom total body-centered cubis 2 atoms face-centered cubic 4 atoms abca hexagonal centered packing- hcp abab like fcc, but only on four sides 3 atoms
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03:14 ionic solids solid containing cations and anions that dissolve in water to give a solution containing  the separated ions, which are mobile and thus free to conduct electrc current positive and negative ions ion-ion attraction ex: NaCl, CaF2, MgO bcc, fcc, square looking molecular solids solid composed of neutral molecules at lattice points molecules with dispersion, dipole-dipole, H bonds ex: Os, H2O, CHCl3 crystals, layers,  covalent!! atomic solids substances that have all atoms occupying the lattice points atoms with dispersion ex: Group 8A, diamond, graphite intertwined ALL METALS metallic solids atoms with a metallic bond ex: Na, Zn, Fe
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03:14 network solids atoms with covalent bond ex: SiO2, C(diamond) 16.4 Structure and bonding in metals closest packing-uniform spheres hexagonal closest packing (hcp) abab spheres are identical except the “b” layer is placed in the dimple of “a” layer 2 atoms Cubic closest packing (ccp) Abc  Fourth layer is like the first 4 atoms calculating the fraction of space occupied by the spheres (fv)= volume occupied by spheres in the unit cell/volume of the unit cell body centered cubic packing 2 atoms edge=4r/(3^.5) bonding in most metals is strong and nondirectional electron sea model-sea of valence electrons, easily moved around (think pounding of  sheet metal) band model- molecular model for metals in which the electrons are assumed to travel  around the metal crystal in molecular orbitals formed from the valence atomic orbitals of  the metal atoms
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03:14 large number of resulting molecular orbitals become closely spaced forming bands metal alloys alloy-substance that contains a mixture of elements and has metallic properties substitutional alloy- some of the host metals are replaced by other metal atoms of  similar size interstitutial alloy- formed when some of the intersitces (holes) in the closest packed  metal structure are occupied by small atoms 16.5 carbon and silicon: network atomic solids network solids directional covalent bonds brittle and do not efficiently conduct heat or electricity ex: diamond and graphite semiconductors
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