The basic assumptions of the kinetic-molecular theory are as follows:
- Gases consist of discrete molecules, which are very small compared with the spaces that exist between them.
- The gas molecules are all in motion. Their motion is continuous, progresses in a straight line, and can have a velocity that is different from those of the molecules around it.
- Collisions between molecules or between a molecule and the wall of its container are elastic. That is, no energy is lost in these collisions.
- Aside from collisions, molecules do not exert forces upon one another.
The kinetic-molecular theory is generally attributed to Rudolf Clasius, who published his theory in 1857. Kinetic-molecular theory attempted to explain Boyle's, Dalton's, Charles', and Avogadro's laws.