Ionic Theory of Solutions and Solubility Rules

Chemists began studying the electrical behavior of substances in the early nineteenth century, and they knew that you could make pure water electrically conducting by dissolving certain substances in it. In 1884, the young Swedish chemist Svante Arrhenius proposed the ionic theory of solutions to account for this conductivity. He said that certain substances produce freely moving ions when they dissolve in water, and these ions conduct an electric current in an aqueous solution.  

Ions are in fixed positions in a crystal. During the solution process, however, ions leave the crystal and become freely moving. Note that Na ions (small gray spheres) are attracted to the negative wire, whereas Cl ions (large green spheres) are attracted to the positive wire. 

Now consider pure water. Water consists of molecnles, each of which is electrically nentral. Since each molecnle carries no net electric charge, it carries no overall electric charge when it moves. Thns, pnre water is a nonconductor of electricity. 

In summary, although water is itself nonconducting, it has the ability to dissolve various substances, some of which go into solution as freely moving ions. An aqueous solution of ions is electrically conducting. 

We can divide the substances that dissolve in water into two broad classes, electrolytes and nonelectrolytes. An electrolyte is a substance that dissolves in water to give an electrically conducting solution. Sodium chloride, table salt, is an example of an electrolyte. When most ionic substances dissolve in water, ions that were in fixed sites in the crystalline solid go into the surrounding aqueous solution, where they are liee to move about. The resulting solution is conducting because the moving ions form an electric current Thus, in genraal, ionic solids that dissolve in water are electrolytes. 

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