Temperature and Phase Changes
When the temperature of a solid is increased, the particles move faster and the attractions become less effective due to the South Street Effect. As the molecules vibrate more and more quickly they reach a point where they are no longer strong enough to hold the particles in place and the solid melts.
Similarly, as the temperature of a liquid is increased, the attractions holding the particles together become less and less effective until the particles are no longer held together and can escape individually as a gas.
Gas particles move around freely, bumping into the walls of the container and each other. When a gas is cooled, the particles slow down and the attractions between them become more and more effective. The collisions between particles become stickier and stickier until the particles stick together and become a liquid.
When a liquid is cooled the particles slow down and as they do the attractions between them become more and more effective until they lock into place as a solid.