Electrons exist in specific, quantized main energy levels (n). They cannot exist between levels.
Shell Capacity
Principal Energy Levels (2n² Rule)
- Each principal energy level is denoted by the quantum number \(n\) (\(n = 1, 2, 3, 4\dots\))
- Maximum number of electrons per level = \(2n^2\)
- Energy levels converge (get closer together) as \(n\) increases
Maximum Electrons per Shell
\(2n^2\)
Shell n=1
2
Shell n=2
8
Shell n=3
18
Shell n=4
32
Physical Insight
Why Energy Levels Converge at Higher n
The electrostatic attraction from the nucleus drops off with distance (following Coulomb's inverse square law). At higher principal quantum energy levels (further from the nucleus), the difference in nuclear attraction between shell \(n\) and shell \(n+1\) decreases rapidly, so the energy gap (\(\Delta E\)) converges towards a limit (\(n = \infty\)).
AQA GCSE & IB Chemistry
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