Final answer:
Water and oil do not mix due to differences in their intermolecular forces, with water molecules bonded by strong hydrogen bonds and oil molecules held by weaker dispersion forces. These differences lead to the immiscibility of water and oil, causing them to form separate layers when combined.
Step-by-step explanation:
When water and oil are mixed, they do not form a solution because of differences in their intermolecular forces. Water molecules are polar and connected by strong hydrogen bonds, while oil molecules are nonpolar and held together by weaker dispersion forces. For a mixture of water and oil to form a solution, the strong hydrogen bonds in water and the dispersion forces in oil must be overcome, which is not energetically favorable as the polar water molecules and nonpolar oil molecules do not experience strong intermolecular attraction. As a result, water and oil remain immiscible, forming two separate layers with oil floating on top due to its lower density.
When immiscible liquids like water and oil are combined, they form distinct layers because the nonpolar oil will not dissolve into the polar water. Different intermolecular attractions, such as the hydrogen bonding in water and dispersion forces in oil, explain why these two substances do not mix and why they have very low mutual solubility. This phenomenon is illustrated by macroscale images where oil forms droplets instead of dissolving in water.