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Unformatted text preview: + ions The bottom layer will contain the same as the top or 1 each Cl-and Na + ions The unit cell has a total of 4 Cl-and 4 Na + ions in it. This equals the empirical formula NaCl . Close packing of spheres Many ions are spherical and many small molecules pack in a crystal lattice as essentially spherical entities. Spheres can pack in three-dimensions in two general arrangements: Hexagonal close packing Cubic close packing The coordination number is the number of particles surrounding a particle in the crystal structure. In each packing arrangement above (hexagonal close pack, cubic close pack), a particle in the crystal has a coordination number of 12 The NaCl (face centered cubic) has a coordination number of 6...
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- Fall '10