surface energy

Surface energy is the energy associated with the intermolecular forces at the interface between two media. This energy per unit area is equal to the surface tension. Surface tension is a property of a liquid's surface that makes it act like a stretched elastic membrane. This property is responsible for phenomena like the spherical shape of small liquid drops and allows certain insects to walk on water.12

The molecules within a liquid attract each other. While molecules deep inside the liquid are pulled equally in all directions, surface molecules experience a net inward pull because there are no molecules above them. This inward pull creates tension. The energy required to remove a unit area of surface molecules is approximately equivalent to the work done to create that surface. Surface tension can be measured in units of energy per unit area, such as joules per square meter.2