dioxide

Everyday

1. A dioxide is a chemical substance whose molecules have two oxygen atoms joined to another atom. tree →
2. In everyday use it almost always means carbon dioxide (CO₂), the gas that people and animals breathe out. tree →

In the lessons

In science, carbon dioxide is a colourless gas: we breathe it out, plants take it in to make food (photosynthesis), fizzy drinks get their bubbles from it, and burning fuels makes it. Too much carbon dioxide in the air traps heat and warms the Earth (climate change). Other dioxides: sulphur dioxide (from volcanoes and pollution), titanium dioxide (white paint).

Examples

• We breathe out carbon dioxide. tree →
• Plants take in carbon dioxide and give out oxygen. tree →
• The bubbles in lemonade are carbon dioxide. tree →
• Burning coal makes carbon dioxide. tree →
• Carbon dioxide is written CO₂. tree →
• Too much carbon dioxide warms the planet. tree →
• Volcanoes give off sulphur dioxide. tree →
• A candle in a jar goes out when oxygen runs low. tree →

Note

Pronounced «dye-OK-side». «Di-» means two (two oxygen atoms). «Carbon monoxide» (one oxygen) is a different, very poisonous gas from faulty heaters — homes need a CO alarm. Carbon dioxide is not poisonous in small amounts.