Question

Why do ionic compounds dissolve in water?

Answer 1

Well, for a start they don't all dissolve.

Explanation:

Some ionic crystals display considerable solubility in water. Water is a protic, dipolar solvent, i.e. `stackrel(delta+)H-stackrel(delta-)O-stackrel(delta+)H`, that can very efficiently solvate many ions. That is the solvent allows charge separation of anion and cation.

However, anions with more than the one unit electronic charge, i.e. oxides, phosphides, carbonates, sulfides, TEND to be quite insoluble. Anyway, chemistry is an experimental science, and you usually have to determine solubility by experiment.