section%204.6%20-%20Ionic%20Crystals - 4.6 Ionic Crystal...

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4.6 Ionic Crystal Structures Objectives Predict crystal structures of ionic compounds. So far we have considered crystal structures of pure elements, like copper or iron. But many crystals actually contain more than one type of atom. In some cases we can consider this extra atom to be an impurity, for example copper as a substitutional impurity in gold to make 14 karat gold, or carbon as an interstitial impurity in iron to make steel. In other cases, however, we need to consider both types of atoms together in determining the crystal structure. The crystal structures of ionic compounds, like NaCl, ZnS, CaF 2 , and CsCl, can be determined by figuring out how the two different types of atoms pack. In order to understand how two different atoms can fit in a crystal, we will start by looking at the SC unit cell. GI 4.6.1 What percentage of an SC unit cell is empty space? GI 4.6.2 Where could you fit another atom into the SC unit cell? GI 4.6.3 Will this atom be the same size as the other atoms, smaller than the other atoms, or larger than the other atoms? GI 4.6.4 How many of these extra atoms can you fit in the unit cell? GI 4.6.5 How many of the original SC atoms are surrounding the extra atom? GI 4.6.6 Based on the size of the atoms, if this were an ionic compound, which atoms would be the anions, the original atoms that make up the SC unit cell, or the atom you added? Explain your answer. An extra atom that fits in between the atoms of a unit cell is called an
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This note was uploaded on 03/30/2010 for the course EMA 3010 taught by Professor Unknown during the Spring '08 term at University of Florida.

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section%204.6%20-%20Ionic%20Crystals - 4.6 Ionic Crystal...

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