This how it works covers How Greenhouse Gases Trap Heat within Greenhouse Effect for GCSE Chemistry. Revise Greenhouse Effect in Atmosphere for GCSE Chemistry with 20 exam-style questions and 12 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 6 of 13 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 6 of 13
Practice
20 questions
Recall
12 flashcards
⚙️ How Greenhouse Gases Trap Heat
Why do CO₂ and CH₄ absorb infrared radiation but N₂ and O₂ do not? The answer lies in molecular structure:
When infrared radiation strikes a molecule, it can be absorbed if the radiation's frequency matches a vibration frequency of the molecule. The molecule vibrates more — essentially warming up. Simple, symmetric molecules like N₂ (two identical nitrogen atoms) and O₂ (two identical oxygen atoms) have vibration modes that don't interact with infrared radiation. They are transparent to infrared.
CO₂, CH₄, and H₂O are asymmetric molecules with multiple vibration modes. These molecules can absorb infrared radiation efficiently. Once absorbed, the excited molecule re-emits the energy as infrared radiation in a random direction — about half goes back towards Earth's surface, adding to the warming effect.
Think of it like a thermal blanket: the thicker and denser the blanket (more greenhouse gases), the less heat escapes to space and the warmer the surface becomes.