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Cell Biology
Bryan Hogeveen

1 2 Solids Measurements of crystal structures are performed Minimal motion using X–ray diffraction spectroscopy Long range structural order (longerthanliquids) See fig. B12.1 p. 447 Crystalline solids = solids with long range internal order. Particles are located at specific sites within the crystal. Amorphous solids = considerable disorder (like glass) 2011 Nobel Prize in Chemistry – Dan Shechtman Quasicrystals – crystals with regular patterns (follow mathematical rules) but never repeat themselves. 3 4 Crystal structure Consider the following 2D pattern To describe the structure of crystals, we need 3D patterns. We use three sets of parallel planes called a lattice that will provide a 3D system for representing the position What is the unit cell? of particles (atoms, ions, molecules). Several choices are possible. The usual convention is to choose the one that indicates all of the symmetry A unit cell is the smallest portion of the crystal that present in the lattice (beyond the scope of this course). when stacked together repeatedly without gaps can reproduce the entire crystal. But not Not smallest ! 5 6 There are 7 systems and 14 types of unit cells that Cubic lattice occur in nature. All planes are equidistant mutualplerpendicul(ar0 ) A cube has 8 corners s eca f 6 edges r e t nec 1 For home Stacking cubes next to each other without gaps, how many cubes does one corner share? A face, an edge or a center? We'll deal mainly with the cubic lattice but tetragonal and orthorhombic with all 90 can be on exams. 7 8 For the cubic lattice, 3 types occur in nature. Simple cubic See Silberberg fig. 12.27 (top) The centers of 8 identical particles (often atoms) define the corners of a cube. Coordination number = how many particles are
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