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