Lab 7 - Solid State Modeling

In this modeling experiment you will build models of

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Unformatted text preview: of the cube. In this modeling experiment, you will build models of a few of the packing arrangements that simple materials can take. The models will focus on the unit ce ll of these structures. The unit cell is the smallest repeating unit in the three dimensional array. You will also explore unit ce ll s toichiome try. We normally think of the stoichiometry of a substance as the ratio of moles of each element. This is reflected in the chemical formula of that substance. This same ratio must also hold in the smallest repeating unit of the solid state, the unit cell. The models will help you visualize the number of each atom or ion inside a unit cell and help you determine the stoichiometry. Packing efficiency and coordination number will also be investigated. The packing e fficie ncy of a unit cell is the fraction of the volume of the unit cell that is occupied by atoms, ions or molecules (commonly expressed as the percent). Thus, as more atoms are packed into a volume, the packing efficiency increases. The coordination numbe r is the number of atoms surrounding another atom in a crystal lattice. The coordination number can also predict trends in packing efficiency. As the coordination number increases, the packing efficiency increases as well. The space in a unit cell that is not occupied by an atom is referred to as the void volume . As void volume increases, packing efficiency decreases. In Part A of the experiment, you will build some simple structures that metallic elements pack in. You may have encountered these in the lecture class. Part B is an exercise in exploring unit cell stoichiometry; finding the ratio of two different ions inside a few unit cells. Equipment 1 Solid- State Model Kit 1 ruler About the Model Kit This model kit was developed by the Institute for Chemical Education at the University of Wisconsin Madison. The instruction pages that follow are reprinted with permission from the Institute for Chemical Education (ICE), John W. Moore, director. The Chemistry Department of North Carolina State University wishes to express thanks to ICE for permission to reproduce th...
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This document was uploaded on 01/22/2014.

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