Why oil will not mix with water?

Water is a polar molecule. This means that a water molecule has a slightly different charge on one side compared to the other. The oxygen atom has a slight negative charge because it is larger, so it accepts more electrons. The hydrogen atom has a slight positive charge because oxygen receives the electrons most of the time. Oil, on the other hand, is a non-polar molecule. Since water is a polar molecule, and polar molecules can only bond with polar molecules, the oil is repelled from the water.