Lecture 15 - Lecture 15Structures of Solids Demonstration:...

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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 nearest-neighbor subunits This leads to the packing of the atoms or molecules as closely as possible These closely packed arrangements are highly symmetric 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. Putting an extra particle inside the cube is more efficient—body-centered cubic. Effectively, the “extra”particles make a second layer over holes in the first layer 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.

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