Liquid water makes one of the best solvents, dissolving many ionic compounds such as table salt. The key to this ability lies in the electric attraction between its hydrogen and oxygen atoms. The positive protons in hydrogen attract negative ions, and the negative oxygen atoms attract positive ions. This creates enough force to break the bond in the ionic compound, dissolving it.
Ionic bonds form between two atoms when one loses an electron, becoming more positive, and another gains an electron, becoming more negative. Opposite electric charges attract each other, so the two atoms stick together. The two atoms together are more stable than they are by themselves. Other electric attractions between atoms are even stronger than the ionic bond; however, so the bond only lasts as long as no stronger forces are present.
In water, two hydrogen atoms bind to one oxygen atom, forming what chemists call a covalent bond. Covalent bonds are very strong. Because of the water molecule’s bent shape, one side is more electrically positive and the other side is more negative. Water molecules attract other molecules and each other because of these charges. When water attracts other charged atoms, they stick, though not as strongly as with a covalent bond. In this case, a hydrogen bond forms.
When you mix an ionic compound, such as sodium chloride, in water, the electric charges in water molecules overpower the ionic bonds, pulling the sodium and chlorine apart and surrounding them with water. The atoms of the salt don’t disappear, but they no longer form the ionic compound. With water molecules in the way, they cannot move close enough to form an ionic bond.
It takes a certain number of water molecules to effectively surround and separate the atoms in an ionic compound. When the water molecules are all occupied with other ions, new ionic molecules do not dissolve; they sink or float on the water and remain a compound. When you add too much of a substance into water and it no longer dissolves, the water is saturated with the ionic compound.