Final answer:
Oil and water do not mix because they have different polarities. Oil is nonpolar while water is polar, causing them to be immiscible. When oil is added to water, it forms droplets that float on the water's surface.
Step-by-step explanation:
Oil and water do not mix together because oil is a nonpolar compound while water is a polar compound. The polarity of water molecules arises from the uneven distribution of charge within the molecule, with oxygen being more electronegative than hydrogen. On the other hand, oil molecules are nonpolar because they have a relatively even distribution of charge. Due to these differences in polarity, oil and water are immiscible, meaning they do not dissolve in each other.
When oil is added to water, it forms droplets rather than dissolving. This is because the polar water molecules attract each other through hydrogen bonding, keeping them tightly packed. The nonpolar oil molecules cannot participate in hydrogen bonding and are unable to mix with water. Instead, the oil molecules cluster together to minimize their contact with water, forming separate droplets that float on the water's surface.