Gases

The gas state of matter is characterized by particles that are widely spaced and move freely at high speeds. These particles are in constant motion and collide with each other and the walls of their container. Because the forces of attraction between the particles are weak, gases do not have a fixed shape or volume and can expand to fill any container they occupy. Gases are highly compressible, as the large amount of space between particles allows for changes in volume when pressure is applied. This state of matter is exemplified by substances like air, oxygen, and helium.