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Week 5 Key Practice Problems

# Week 5 Key Practice Problems - CHEMISTRY 201X Practice...

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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? λ = 154.178 pm Left: d = a = 336.8 pm sin θ = n λ /2d = 0.2289n n = 1: sin θ = 0.2289 2 θ = 26.46 ° n = 2: sin θ = 0.4598 2 θ = 54.49 ° ALL OBSERVED n = 3: sin θ = 0.6867 2 θ = 86.74 ° Middle: d = a/ 2 = 238.2 pm sin θ = n λ /2d = 0.3237n n = 1: sin θ = 0.3237 2 θ = 37.77 ° n = 2: sin θ = 0.6474 2 θ = 80.69 ° JUST n=1 and n=2 n = 3: sin θ = 0.9711 2 θ = 152.38 ° Right: d = a/ 3 = 194.5 pm sin θ = n λ /2d = 0.3964n n = 1: sin θ = 0.3964 2 θ = 46.71 ° n = 2:

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Week 5 Key Practice Problems - CHEMISTRY 201X Practice...

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