Lecture 27_Solids_Spirng09 (1)

Lecture 27_Solids_Spirng09 (1) - CHM 11500 Lectures 27 and...

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CHM 11500 CHM 11500 Lectures 27 and 28 Lectures 27 and 28 Solids, Ceramics Solids, Ceramics Reading: Sections 13.6-13.8; pp. 619-629 Next time: Interchapter: The Chemistry of Modern Materials; pp. 643-655
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Crystalline Solids When most liquids are cooled, they eventually freeze and form crystalline solids: atoms, ions, or molecules are arranged in a definite repeating pattern .
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- Unit Cell - Crystal Systems The cubic systems (SC, BCC, FCC) Packing arrangements Packing efficiency Crystalline Solids Relation between crystal density and atomic radius
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portion of a 3-D lattice The crystal lattice and the unit cell lattice point unit cell portion of a 2-D structure unit cell lattice point lattice parameter (a) lattice parameter (a)
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The three cubic unit cells 1) Simple Cubic coordination number = 6 (nearest neighbors) Atoms/unit cell = 1/8 x 8 = 1 1/8 atom at 8 corners
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2) Body- centered Cubic coordination number = 8 1/8 atom at 8 corners 1 atom at center Atoms/unit cell = (1/8 x 8) + 1 = 2 The three cubic unit cells
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3) Face- centered Cubic coordination number = 12 Atoms/unit cell = (1/8 x 8)+(1/2 x 6) = 4 1/8 atom at 8 corners 1/2 atom at 6 faces The three cubic unit cells
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Question 1 Barium crystallizes with a body-centered unit cell with the length of the cell edge - lattice parameter or a - of 502.5 pm . What is the radius (R) of a Ba atom? (enter a number with no decimal places)
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Solution to Question 1 a a f a a f a 2 + a 2 = f 2 √2 a = f lattice parameter
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Solution to Question 1 a a d f a 2 + f 2 = d 2 √2 a = f a 2 + 2 a 2 = d 2 3 a 2 = d 2 √3 a = d Radius = d / 4 = (√3 a)/4 = 0.433 x 502.5 pm f a d a f
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Body- centered Cubic coordination number = 8 1/8 atom at 8 corners 1 atom at center Atoms/unit cell = (1/8 x 8) + 1 = 2 Cell diagonal = 2 atoms Radius = 1/2 x atom’s diameter Cell diagonal = 4 x radius The three cubic unit cells
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a f a d f a 2 + f 2 = d 2 √2 a = f a 2
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Lecture 27_Solids_Spirng09 (1) - CHM 11500 Lectures 27 and...

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