We all have observed that Oil and Water do not mix with each other. Oil floats on water surface. But have you ever thought of the reason behind it?. Here is a basic scientific explanation of this behaviour.
Water, as we know, is the most common of the solvents. Many substances like Salt, Sugar etc. dissolve in water. Others like Wax, Oil, Fat etc. do not. There is a scientific principle “Like dissolves Like”. Only those substances make solutions which have similar types of molecules. For any substance to dissolve or mix with water, its molecules must be capable of forming electrostatic bond with water molecules.
Water molecules are Polar. That is, one side of each water molecule has a partial Positive and the other side has a partial Negative charge. For example, the molecules of Sodium Chloride have Ionic or Polar characteristics. Therefore Salt when put in Water dissolves in it. The Polar Molecules of Water are attracted towards the charged Sodium and Chloride ions and forms a cluster around them. This in turn reduces the attraction between Sodium and Chloride Ions. They separate and spread through the water and forms a solution.
The Molecules of Oil are different from that of Water. They are much bigger than Water Molecules and contain much more atoms in them. Oil Molecules have Covalent Bonds. The force of attraction between Water and Oil Molecules is less than that between the Oil Molecules. Hence Oil Molecules do not mix with water and float on water and they do not dissolve in Water.