The structure of water makes it a polar molecule. This shows each hydrogen atom contain a slight positive charge, while the oxygen contain a slight negative charge.
Ionic compounds are crystalline in nature that contain the same number of both positive and negative ions. When you dissolve these ionic compounds in water, its molecules begin to attract water ions, which causes a separation between the ionic molecules. These atoms of hydrogen contained in water molecules are nearest to the ions of the compound with a negative charge, while the atoms of oxygen in the water molecule is nearest to the ions of ionic compounds with a positive charge.
Create a picture of each one of the ionic compounds enveloped by molecules of water and you will be able to get an idea of the reaction that takes place, but know that the reaction occurs at a very rapid rate the moment you add the compound to water.
This is nothing more than just a physical change because once you remove the water from the ionic compound, the compound is recovered back without any change.