# Explain why carbon dioxide is classified as a greenhouse gas but diatomic gases such as nitrogen and oxygen are not.

> IB DP Physics Standard Level (2023 syllabus) — B.2 Greenhouse effect · Explain · 4 marks

> The concentration of carbon dioxide in Earth's atmosphere has increased significantly since industrialisation, contributing to enhanced global warming. Not all atmospheric gases, however, contribute to the greenhouse effect.

## Mark scheme (4 marks)

1. Greenhouse gases absorb (and re-emit) infrared radiation emitted by the Earth's surface.
2. CO₂ (and other greenhouse gases) are polyatomic molecules whose natural vibrational frequencies correspond to frequencies in the infrared region of the electromagnetic spectrum.
3. Diatomic homonuclear molecules such as N₂ and O₂ are symmetrical, so their vibrations do not produce a change in electric dipole moment.
4. Because N₂ and O₂ cannot absorb infrared radiation, they do not contribute to warming the atmosphere / do not act as greenhouse gases.

## Key terms

- [greenhouse gas](https://www.gradenine.co.uk/glossary/greenhouse-gas)

## Related

- [Revision notes for IB DP Physics Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-carbon-dioxide-is-classified-83d8407b) · Published by Druglandscape Ltd.