PPT Slide

45

• An important crystal structure for ionic salts with a cation/anion  ratio of 1/2 is the fluorite (CaF 2) structure.

• The CaF 2 unit cell consists of a face-  centered cubic array of Ca 2+ ions  tetrahedrally surrounding eight F ñ ions.

• Four Ca 2+ ions + eight F ñ ions per unit cell.

• The properties of ionic solids are a direct  consequence of the fixed ion positions and  strong attractive forces (high lattice energy).

• Thus, ionic solids have high melting points and low electrical  conductivities.

• Ionic compounds are hard because only a strong external force can  change the relative positions of the many interacting ions.

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