And now, I'm not only talking about the molecules on the surface of the water. Now I'm talking all the molecules found within the entire system gain enough kinetic energy. So when you boil something, you see bubbles forming from the inside that travel to the up. It's the outside. And that's because those molecules found inside gain enough kinetic energy, they become gas molecules, and they travel up. The Boiling point is also the point at which vapor pressure created by the liquid is equal to or greater than the total pressure found above the system.