Explaining the Behavior of Gases
The kinetic-molecular theory helps explain the behavior of gases.CROSSCUTTING CONCEPTS
Systems and System Models Review the assumptions made by the kinetic-molec-
ular theory.For example, the 
constant motion of gas particles allows a gas to expand until it fills its container, such as 
when you inflate a beach ball.Thus, 
there are fewer chlorine molecules than gold atoms in the same volume.Develop your own visual or physical representation to help others 
understand the kinetic-molecular theory and the behavior of gases.Compression and expansion
If you squeeze a pillow made of foam, you can compress it; that is, you can reduce its 
volume.When the volume of a container is made larger, the random motion of the 
particles fills the available space.Figure 3 illustrates what happens to the density of a 
gas in a container as it is compressed and as it is allowed to expand.Air, which is a mixture of gases, is also compressible.