Question

Using an argument based on intermolecular forces, explain why there is a surface tension that develops between air and water? How would a surfactant disrupt this tension?

Answer 1

In a sample of water, there are two types of molecules. Those that are on the outside in contact with air and those that are on the interior (or "bulk"). The interior molecules are attracted to all the molecules around them, while the exterior molecules are attracted to only the other surface molecules and to those below the surface, since there are no water molecules above them. This makes it so that the energy state of the molecules on the interior is much lower than that of the molecules on the exterior. Because of this, the molecules try to maintain a minimum surface area, thus allowing more molecules to have a lower energy state. This is what creates what is referred to as surface tension.
The water molecules attract one another due to the water's polar property. The hydrogen ends, which are positive in comparison to the negative ends of the oxygen cause water to "stick" together. This is why there is surface tension and takes a certain amount of energy to break these intermolecular bonds. Same goes for other liquids, even hydrophobic liquids such as oil.