Explain what happens to the electrons inside an atom when the atom absorbs electromagnetic radiation, and what is observed when those electrons subsequently lose energy.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Atoms can absorb electromagnetic radiation and later release it. This process produces observable evidence about the structure of atoms.
Model answer (5 marks)
Electrons absorb a photon of electromagnetic radiation and gain the photon’s energy.
The electron is promoted to a higher energy level – it becomes excited.
When the electron subsequently returns to a lower (often the original) energy level, it releases the excess energy.
A photon is emitted during this transition.
Only photons of specific frequencies (wavelengths) are emitted, giving a line emission spectrum.
The electron is promoted to a higher energy level – it becomes excited.
When the electron subsequently returns to a lower (often the original) energy level, it releases the excess energy.
A photon is emitted during this transition.
Only photons of specific frequencies (wavelengths) are emitted, giving a line emission spectrum.
Examiner tips
- Use the word ‘photon’ and ‘excited’ to show understanding of absorption.
- Show the sequence: absorb → excited → emit → line spectrum.
- Mention that the emitted photon has the same energy difference as the absorbed one.
- Keep the answer concise – 5 marks allow a short paragraph.
Common mistakes
- Confusing absorption with emission – forgetting to mention the photon is absorbed first.
- Saying the electron ‘loses energy’ without specifying that it emits a photon.
- Giving a continuous spectrum instead of a line spectrum.
Mark scheme (5 marks)
- Electrons absorb a photon (of radiation) / electrons gain energy from the absorbed radiation
- The electron moves to a higher energy level (is excited to a higher energy level)
- The electron then falls back down to a lower energy level (returns to a lower / original energy level)
- A photon is emitted when the electron drops to a lower energy level
- Only specific frequencies (wavelengths) of light are emitted, producing a line emission spectrum
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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