Assemblies of Ions and the Ionic Model

In Chapter 1 an ionic solid was defined as a lattice composed of anions and cations, where the atoms have lost or gained electrons to become ions. The loss or addition of electrons effectively completes a stable octet of outer electrons to create the ion. 

The general structure of ionic solids results in the following properties  

High melting points. Ionic compounds contain strong non-directional interactions where the electrostatic attraction of 

Electrical Conductivity. In the solid the ions are fixed on their lattice sites and electrical conductivity is poor. However, in the molten state the ions are free to move and conduct electricity in the presence of an electric field. 

Coordination numbers. Ionic compounds containing cations and anions tend to show much lower coordination numbers than metallic lattices, but higher than covalently bonded compounds. This is due to the relatively small size of the cations and relatively large size of the anions. It is not geometrically feasible to locate many large anions closely around each cation. 

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