Electron Arrangement and Energy Levels Revision Notes | GCSE AQA Higher Physics
Energy levels are fixed distances from the nucleus where electrons can exist. Free GCSE AQA Physics notes with key definitions and 14 questions answered.
Updated 20 Mar 2026 · Revise Right Team
Electron Arrangement and Energy Levels is part of Atoms and isotopes in GCSE AQA Higher Physics.
3 min
Reading time
23
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GCSE AQA Higher
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What this lesson covers
Energy levels are fixed distances from the nucleus where electrons can exist. Free GCSE AQA Physics notes with key definitions and 14 questions answered.
Explain how electrons are arranged at different distances from the nucleus in energy levels
Describe what happens when electrons absorb electromagnetic radiation
Describe what happens when electrons emit electromagnetic radiation
Apply knowledge of electron energy changes to explain absorption and emission of electromagnetic radiation
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Use this lesson to stay inside Atoms and isotopes while connecting the detail back to the wider Atomic structure topic.
Atomic structure
Atoms and isotopes
GCSE AQA Higher Physics
Revision notes
Read the core explanations from Electron Arrangement and Energy Levels before testing yourself from memory.
1. Why Electrons Don't Just Fall Into the Nucleus
Here's something that puzzled scientists for decades: if electrons are negatively charged and the nucleus is positively charged, why don't they just crash together? The answer revolutionised our understanding of atoms.
Electrons can't exist anywhere they want around the nucleus. They're restricted to specific distances - like being forced to stand on particular rungs of a ladder, never between them. These fixed positions are called energy levels.
Think of energy levels like the floors of a building. An electron can be on the ground floor, first floor, or second floor - but never floating between floors. The ground floor (closest to nucleus) requires the least energy to reach.
2. How Electrons Jump Between Energy Levels
Electrons can move between energy levels, but only in specific ways. They need exactly the right amount of energy to make the jump - like needing the exact change for a vending machine.
When an electron absorbs electromagnetic radiation (like light), it gains energy and jumps to a higher energy level - further from the nucleus. This is called excitation. The electron has moved from a lower energy level to a higher one.
But electrons don't stay excited forever. They naturally fall back down to lower energy levels, releasing the extra energy as electromagnetic radiation. This is called emission.
3. Ground State vs Excited State
Most of the time, electrons occupy the lowest possible energy levels. This minimum-energy arrangement is called the ground state - it's the atom's natural, relaxed condition.
When energy is added, electrons can move to higher energy levels, creating an excited state. But this doesn't last - excited electrons quickly fall back down, releasing energy as light.
Worked example: Electron Energy Changes in Hydrogen
A hydrogen electron absorbs energy and moves from energy level 1 to energy level 3. Describe what happens next when it returns to the ground state.
Electron absorbs energy: Level 1 → Level 3 — The electron has been excited to a higher energy level
Level 3 is an excited state - unstable — Electrons naturally want to return to lower energy levels
Electron falls back: Level 3 → Level 1 — Could happen in one jump or via Level 2
Electromagnetic radiation is emitted — The energy difference is released as light
Answer: The electron will emit electromagnetic radiation and return to energy level 1 (ground state)
4. Electron Transitions and Emission
When electrons change energy levels, they absorb or emit electromagnetic radiation.
Each element has its own unique pattern of energy levels. When electrons fall from higher to lower levels, they emit specific frequencies of light. Different energy gaps produce different colours - this creates each element's unique 'fingerprint' of light.
This shows that electrons can only move between specific energy levels.
5. Common Mistakes and Exam Success
Students often get confused about the direction of energy changes. Remember: absorption means gaining energy and moving to higher levels (further from nucleus). Emission means losing energy and moving to lower levels (closer to nucleus).
Another trap: thinking electrons can exist anywhere around the nucleus. They can't - only at specific energy levels. It's like a staircase, not a ramp.
Sources and content standards
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-20.
Electromagnetic radiation is energy carried by waves, including visible light, radio waves, microwaves and X-rays. When it is absorbed by electrons, it provides the energy they need to move to higher energy levels.
What are energy levels in an atom?
Energy levels are fixed distances from the nucleus where electrons can exist. The first energy level, closest to the nucleus, has the lowest energy, and energy increases further out; electrons can never exist between energy levels.
What is the difference between ground state and excited state?
The ground state is the lowest energy arrangement of electrons in an atom, the most stable configuration. An excited state is when one or more electrons have absorbed energy and moved to higher energy levels; it is temporary and unstable, so electrons quickly fall back down.
Which energy level has the lowest energy?
The first energy level, closest to the nucleus, has the lowest energy, and the energy increases moving further out. In the ground state, electrons occupy the lowest available energy levels.
What happens when an electron absorbs electromagnetic radiation?
When an electron absorbs electromagnetic radiation, it gains energy and moves to a higher energy level, further from the nucleus. This is called excitation, and the electron needs exactly the right amount of energy to make the jump.
What happens when an electron moves to a lower energy level?
When an electron falls back to a lower energy level, closer to the nucleus, it loses energy and emits electromagnetic radiation. This is called emission; the energy difference between the levels is released as light.
Why do different elements emit different colours of light?
Each element has its own unique pattern of energy levels, so when electrons fall from higher to lower levels they emit specific frequencies of light. Different energy gaps produce different colours, creating each element's unique fingerprint of light.
What is excitation of an electron?
Excitation is when an electron absorbs electromagnetic radiation, such as light, gains energy and jumps to a higher energy level, further from the nucleus. The electron then falls back down, releasing the energy.
What is emission in atoms?
Emission is when an excited electron falls back to a lower energy level, closer to the nucleus, and releases the extra energy as electromagnetic radiation. Electrons do not stay excited forever.
What happens when a hydrogen electron moves from level 1 to level 3?
A hydrogen electron that absorbs energy and moves from energy level 1 to level 3 is in an unstable excited state. It falls back to level 1, the ground state, either in one jump or via level 2, emitting electromagnetic radiation.
Can electrons exist between energy levels?
Electrons cannot exist between energy levels; they can only be at specific, fixed distances from the nucleus, like standing on the rungs of a ladder but never between them. Energy levels are like a staircase, not a ramp.
Do electrons gain or lose energy moving away from the nucleus?
Electrons gain energy when they move away from the nucleus to a higher energy level, by absorbing electromagnetic radiation. They lose energy, emitting radiation, when they move to a lower level closer to the nucleus.
Why do excited electrons fall back down?
Excited electrons fall back down because an excited state is temporary and unstable. They return to lower energy levels, towards the ground state, and release the energy difference as light.
Why do electrons not fall into the nucleus?
Electrons do not fall into the nucleus because they can only exist at specific, fixed distances from it, called energy levels. They are restricted to these levels, like being forced to stand on particular rungs of a ladder.