Why Water And Oil Don't Mix

The water molecule is made up of two hydrogen atoms and one oxygen atom. Due to the ability of the oxygen atom to pull the hydrogen electrons owards itself, it carries a negative charge. As a result, the hydrogen atoms carry a more positive charge. The charges of these two molecules allow them to make weak bonds with certain particles, like NaCl. NaCl dissociates into a Na+ which is attracted to the negative oxygen atoms of the water molecules and hangs out there, and the Cl- which is attracted to the positive hydrogen atoms in the water molecules and hangs out with them. Likewise, molecules which have lots of charges on them are termed hydrophillic, or "water loving." They interact well with the charges on water molecules. Unlike the water molecule, oil is made up of long chains of carbon atoms (usually 8 Carbon atoms) which do not carry an electric charge. These long chains without a charge are called hydrophobic - or "afraid of water." Because they do not have a charge, there is no attraction between the charges on the water molecule and the long carbon chains and can't hang out with the water molecules. That is why oil does not mix with water. It is because it cannot form any bonds with water.