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Week 5 Practice Problems

Week 5 Practice Problems - lead is 4.950 Å If X-rays with...

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CHEMISTRY 201X September 17-21, 2007 Practice Problems (45) Polonium adopts a “simple cubic” structure at room temperature and pressure. The unit cell is a cube, side is a = 336.8 pm, and contains Po atoms just at the corners. Vertical direction is parallel to a side of the cubic unit cell ( a ). Vertical direction is parallel to a diagonal of a square face of the cubic unit cell ( 2 a ). Vertical direction is parallel to the body diagonal of the cubic unit cell ( 3 a ). For Cu X-radiation, calculate the angles 2 θ where Bragg reflections would be observed for each set of planes for n = 1, 2, and 3. If the X-ray diffractometer could only observe reflections for 2 θ 90 ° , which reflections would be observed? (46) The distance between members of a set of equally spaced planes of atoms in crystalline
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Unformatted text preview: lead is 4.950 Å. If X-rays with λ = 1.936 Å are diffracted by this set of planes, calculate the scattering angles 2 θ at which first-order, second-order, third-order, and fourth-order ( n = 1, 2, 3, 4) will be observed. (47) Bragg’s equation contains sin θ , where 2 θ is the angle between the incident X-ray beam and diffracted X-ray beam. Since sin θ ≤ 1, this places a limit on what can be observed in a crystal. (a) Use the Bragg equation and deduce the limitation on d-spacings between planes of atoms when Cu K α X-radiation is used ( λ = 1.54178 Å), when Mo K α X-radiation is used ( λ = 0.71069 Å)....
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