Kinetic Model
Atoms or molecules in matter tend to attract one another when they are far apart, and repel each other when they are too close together. This has to do with the fact that an atom is made up of electrons surrounding a nucleus, but we shall not go into that here.
The attractive forces cause atoms to come together to form solids. As they come closer and closer, there is a point when the attractive forces become repulsive. (This happens when the electrons get too close.) Then they stop coming closer. The distance between them would be the distance between atoms in the solid.
This situation is only possible if the atoms do not have much energy, or else they would just bounce right off each other. This in turn happens when the temperature is low enough for the material to be solid.
When temperature is increased, the atoms gain energy. In the solid, the vibration of the atoms increases. When temperature is high enough, there is enough energy to overcome some of the attractive forces, and the atoms can start moving around. This is when the solid melts into a liquid.
If the temperature is increased even further, the atoms would eventually have so much energy that they overcome all of the attractions. Then they no longer stay close to each other, but move apart completely. The liquid boils and turn into a gas.
Copyright 2010 by Kai Hock. All rights reserved.
Last updated: 5 October 2010.