Water can dissolve so many different substances that it is often called the universal solvent. What makes water so special? The oxygen atom of a water molecule holds electrons more strongly than the hydrogen atoms. The shared electrons in the two covalent bonds, therefore, are drawn closer to the oxygen. As a result, the oxygen takes on a slightly negative charge and the hydrogens a slightly positive charge. Because of the molecule's shape, one end is positive and the other end negative.
Water molecules can act as little magnets. The positive ends of water molecules are attracted to solute particles that have a negative charge. The negative ends of water molecules are attracted to positively-charged solute particles.
Water dissolves most ionic solids because its molecules pull apart the ions that make up the solid. Water can also form a solution with molecules that have slightly negative and slightly positive parts. However, because molecules of fats and oils have their electrical charges evenly distributed, they repel water molecules instead of attracting them.
