The Seasons
The Seasons

You know that water is a liquid, ice is a solid, and steam is a gas. But what exactly is a gas? The molecules in a solid are stable. They don’t move and they’re packed closely together. The molecules in a liquid are spaced farther apart. But the molecules in a gas are active. They move around – a lot – and they’re spaced very far apart.

Fun Facts

  • Vapor is a gas that’s a liquid at room temperature, such as water. Steam is a vapor.
  • Our atmosphere is made up of layers of gases that protect our planet.
  • Solids can only take their own form; liquids can spread to fill the bottom of a container; gases can fill a container of any size and any shape.
  • Some gases are flammable.
  • Gases can be tightly compacted under high pressure. When the pressure is lowered, the gases are released with force. Opening a bottle of soda is an example of this. The carbon dioxide gas in the soda causes a rushing sound or bubbles to foam up.


Gas: a form of matter with molecules that move and that are widely spaced

Flammable: easily catches on fire

Vapor: a gas that’s a liquid at room temperature, such as water

Q and A

Question: Are gases dangerous?

Answer: Some gases, such as natural gas, are dangerous because they’re highly flammable and can explode. Others, such as carbon monoxide, can make people sick. Not all gases are dangerous.

Learn More

Visit the American Chemistry Society to learn about the fizz in soda pop.

Head over to Purdue University for a demonstration of what gas molecules look like.