Arrangement of Ions in Ionic Compounds

Ions of opposite charge strongly attract each other. Ions of like charge strongly repel each other. As a result, ions in an ionic compound are arranged in a specific way. Positive ions tend to be near negative ions and farther from other positive ions.
The placement of ions in an ionic compound results in a regular, repeating arrangement called a crystal lattice. A crystal lattice is made of huge numbers of ions. A crystal lattice gives the compound great stability. It also accounts for certain physical properties. For example, ionic solids tend to have high melting points.

Ionic compounds are made of nearly endless arrays of ions. A chemical formula for an ionic compound shows the ratio of ions present in the crystal lattice. It does not show the actual number of ions.

Each ionic compound has a characteristic crystal lattice arrangement. This lattice arrangement gives a particular shape to the crystals of the compound. For example, sodium chloride forms cubic crystals.

The crystal shape of an ionic compound is of great importance to geologists in identifying minerals. There are more than 2000 different kinds of minerals, and many of them look alike! One of the properties by which minerals are classified is crystal shape. There are six basic crystal shapes, or systems, and each of the thousands of minerals belongs to one of these systems.

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