When a liquid is heated beyond it's boiling point it converts to gas. Matter that is composed of liquid is essentially atoms that are more loosely packed than a solid but still closer to each other as compared to gases. Under low pressures and high temperatures the atoms in a liquid oscillate at greater rates and drawn further apart which causes them to break free from the forces they exert on each other and convert to a gaseous state. For example, when we heat water at a temperature of 100 degrees C under ground level pressure it is converted to water vapor.
