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Solids. crystalline. quartz. well defined structures. amorphous. glass. no orderly structure. SiO 2. crystal lattice. system of points. describes arrangement of particles. unit cell. repeating structural unit. lattice. 7 unit cells. simple cubic. formed from packing spheres.
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Solids crystalline quartz well defined structures amorphous glass no orderly structure SiO2 crystal lattice system of points describes arrangement of particles
unit cell repeating structural unit lattice 7 unit cells simple cubic formed from packing spheres
crystalline solids unit cells hexagonal closest packing cubic packing in 3 dimensions hexagonal closest pack cubic closest pack simple cubic body centered cubic “abab” layers “abca” layers “abab” layers “aaa” layers
Three-Dimensional Cubic Lattices Simple cubic a a a 1/8 x 8 = 1 particle coordination number = 6 Body-centered cubic a b a b (1/8 ) x 8 + 1 = 2 particles coordination number = 8 Face-centered cubic cubic closest pack a b c a b c (1/8 ) x 8 + (1/2 ) x 6 = 4 particles coordination number = 12
Calculation of atomic radii Cu faced-centered cubic density = 8.92 g/cm3 r+2r+r mass = 63.546 g/mol 63.546 g 4 atoms 1 mol cm3 unit cell 6.022 x 1023 atoms mol 8.92 g 1/3 = 3.617 x 10-8 cm ( ) 4.732 x 10-23 cm3 / unit cell lattice parameter, a = (4r)2 (3.617 x 10-8)2 + (3.617 x 10-8)2 1 x 10-2 m 1 pm r = 1.279 x 10-8 cm = 127 pm 1 x 10-12 m 1 cm
d X-Ray Diffraction by Crystals diffraction interference between waves caused by object in their path constructive or destructive Bragg Equation n = 2d sin
Types of Crystalline Solids Covalent Ionic Molecular molecules in lattice atoms in lattice ions in lattice m.p. depends on bonding forces ionic covalent H-bonding H2O 0oC Cdiamond 3550oC NaCl 800OC
Covalent solids atoms in lattice carbon sp3 sp2 sp2 diamond graphite buckminsterfullerene hardest material known conduct electricity - e- doesn’t conduct electricity
Covalent solids atoms in lattice atom of 1 metal metals every lattice point - body-centered cubic face-centered cubic melting point hexagonal close packed Na 97oC share valence e- e- “sea” Cr 1890oC good conductors substitutional alloy brass steel interstitial alloy
Ionic Solids composed of charged species – unit cell neutral stoichiometry of compound each unit cell - anions and cations different in size anions at lattice points cations in “holes” NaCl face-centered cubic CsCl simple cubic r = 0.225 R r = 0.414 R too small trigonal hole tetrahedral hole octahedral hole
Molecular Solids molecules in lattice hemoglobin reaction center 1962 1988 Perutz and Kendrew Deisenhofer, Huber and Michel