Stuctural formula of carbon dioxide. C is carbon and O is oxygen. The double lines represent the double chemical bond between the atoms.

A picture to show simply how the atoms may fill space. The black is carbon and the red is oxygen.

Carbon dioxide (CO₂) is a chemical compound and is acidic. It is a gas at room temperature. It is made of one carbon and two oxygen atoms. People and most animals release carbon dioxide when they breathe out. Also, every time something organic is burnt (or a fire is made), it makes carbon dioxide. Plants use carbon dioxide to make food. This process is called photosynthesis. The properties of carbon dioxide were studied by the Scottish scientist Joseph Black in the 1750s.