21_562ln08

21_562ln08 - MIT OpenCourseWare http:/ocw.mit.edu 5.62...

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MIT OpenCourseWare http://ocw.mit.edu 5.62 Physical Chemistry II Spring 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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5.62 Spring 2008 Lecture Summary #21 Page 1 THERMODYNAMICS OF SOLIDS: EINSTEIN AND DEBYE MODELS Reading: Hill, pages 86-98 For the next few lectures we will discuss solids, in particular crystalline solids, in which the particles are arranged in a regular lattice. The lattice could consist of single atoms or atomic ions, such as Ar or Na + Cl arranged in something like a face-centered-cubic (FCC) or body-centered-cubic (BCC) crystalline array. Or the lattice could be a crystal of more complex molecules in a lattice, such as CO, CO 2 , H 2 O, penicillin, hemoglobin, etc. TOTAL # DEGREES OF FREEDOM = 3N (where N = # of atoms in the crystal) 3 correspond to overall translation 3 correspond to overall rotation ! " # of whole crystal remaining 3N–6 correspond to internal vibrations within crystal In this treatment the crystal is viewed as a giant polyatomic molecule undergoing simple harmonic motion in each of its 3N-6 vibrational normal modes. The behavior of such a harmonic molecular crystal is described by the normal modes of vibration. There are 3N–6 harmonic oscillators that can be treated independently (a convenient idealization) to describe the motions and energies within the crystal. There are many kinds of vibrations in a crystal. Viewed along a particular
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This note was uploaded on 11/27/2011 for the course CHEM 5.43 taught by Professor Timothyf.jamison during the Spring '07 term at MIT.

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21_562ln08 - MIT OpenCourseWare http:/ocw.mit.edu 5.62...

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