Section 1 of 7Energy levels
Fixed orbits
- Fixed orbits Electrons orbit the nucleus only at certain distances, called energy levels or shells.
Capacity
- Capacity Each level holds a limited number of electrons: two in the first, eight in the second and eight in the third (as met in chemistry).
Higher means more energy
- Higher means more energy The further an electron is from the nucleus, the more energy it has, a bit like being higher up a ladder.
Section 2 of 7Absorbing radiation
1Radiation arrives
- Radiation arrives Electromagnetic radiation, such as light or infrared, hits an atom.
2Electron absorbs energy
- Electron absorbs energy The electron takes in a packet of energy from the wave.
3Moves up a level
- Moves up a level It jumps to a higher energy level and the atom is now in an excited state.
4Radiation removed
- Radiation removed The wave has lost energy, so it is absorbed by the material.
Section 3 of 7Emitting radiation
1Excited state is unstable
- Excited state is unstable The electron does not stay in a high level for long.
2Falls to a lower level
- Falls to a lower level It drops back to a lower energy level closer to the nucleus.
3Energy is released
- Energy is released The energy difference leaves as a burst of electromagnetic radiation.
4Colour
- Colour If the radiation is visible, its frequency decides the colour; larger jumps give higher frequencies.
Section 4 of 7Comparison
| Process | Electron moves | Radiation | Energy of electron |
|---|---|---|---|
| Absorption | Up to a higher level | Taken in | Increases |
| Emission | Down to a lower level | Given out | Decreases |
Section 5 of 7Explaining everyday observations
1
Dark objects look dark because their electrons absorb most of the visible light that arrives, and little is reflected.
2
This is also why dark surfaces warm up faster in sunlight.
3
Hot or electrically excited gases give out light because electrons fall between levels and emit radiation.
4
Each jump emits a particular frequency, so each element gives a characteristic set of colours.
5
At GCSE physics you do not need the filling order of shells; this belongs to chemistry.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Energy level | A fixed distance from the nucleus at which an electron can orbit, also called a shell. |
| Excited state | The condition of an atom when an electron has moved to a higher energy level. |
| Absorption | Taking in energy from radiation. |
| Emission | Giving out energy as electromagnetic radiation. |
| Electromagnetic radiation | Waves of electric and magnetic fields that transfer energy, including light. |
Section 7 of 7Exam technique
1
Saying electrons can orbit at any distance: only certain energy levels are allowed.
2
Reversing the directionelectrons move up when they absorb radiation and down when they emit it.
3
Thinking electrons leave the atom when they move up a level: this is only ionisation, which takes more energy.
4
Forgetting that the emitted frequency is set by the size of the jump.