Dissolving salt in water is an example of a chemical change. The dissolution leads the salt to break into sodium and chlorine ions, so it alters its essential chemical properties. Even though boiling salt water ends up leaving behind a residue of salt, while the salt and water are together, the chemical processes change enough to be viewed as a chemical reaction.
Salt is formed out of the ionically bonded elements of sodium and chlorine; the fact that water molecules are polar, with a slightly positive charge on one end and a slightly negative charge on the other means that water has the power to break some of these ionic bonds. The polarity in the salt molecules mirrors that of the water molecules, making it even easier for the water to break up the salt molecules, causing the salt to dissolve.
The process of breaking up the salt molecules involves the matching of opposite magnetic poles. The hydrogen end of the water molecule takes on a slightly positive charge, attracting the slightly negative chloride end of the salt molecule. This attraction also takes place between the slightly positive sodium end of the salt molecule and the slightly negative oxygen end of the water molecule.