Question

why does soap lower the surface tension of water? I know that there is a slight difference in the water molecules in front of and behind the raft but why?

Answer 1

what causes surface tension? intermolecular forces, more importantly H-bonds in water. "surfactants reduce the surface tension of water by adsorbing at the liquid-gas interface" ( http://en.wikipedia.org/wiki/Surfactant) ..basically surfactants get in the way of the IMFs at the surface.