A Little Bit About Molecular Motion
Molecules/atoms in gases, liquids, and (believe it or not) even solids are constantly in motion to varying degrees. As a substance is heated, the kinetic energy of the molecules of that substance increases and the molecules move around faster. In a liquid, the molecules are close enough together that they experience attractive (sticky) forces between one another. These attractive forces weakly bind the molecules together into little packs or chains but can be easily overcome as the molecules move around and vibrate. The degree to which molecules of a substance stick to each other is called its “surface tension”. The surface tension of water is what allows water skippers to walk on the surface of water. In a gas, however, the molecules are far apart and are not close enough to other molecules to experience attractive forces. Additionally, the molecules in a gas are moving so fast that when two molecules do collide, they pretty much just bounce off each other instead of sticking.