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Lecture 15—Structures of Solids
Demonstration: properties of crystalline salts, hydrogen bonded solids, and metals
The driving force for crystallization is to maximize the interactions (minimize the
enthalpy) of nearestneighbor subunits
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This leads to the packing of the atoms or molecules as closely as possible
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These closely packed arrangements are highly symmetric
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One simple, symmetrical packing arrangement is a cubic lattice.
However, this
packing leaves a considerable amount of empty space, and the interactions are not
maximized.
Only one element, polonium, crystallizes this way.
The structure is
relatively rare compared to the next three.
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Putting an extra particle inside the cube is more efficient—bodycentered cubic.
Effectively, the “extra”particles make a second layer over holes in the first layer
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The most efficient packing arrangements are based on a hexagonal lattice, where
a second, and sometimes a third, layer are packed over sets of holes in the first
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This note was uploaded on 09/29/2009 for the course ME 530.230 taught by Professor Katz during the Spring '09 term at Johns Hopkins.
 Spring '09
 KATZ

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