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💡 Filling the shells
Electrons are seated shell by shell, like guests filling the front rows first. Bohr and Bury gave the simple rules for who sits where.
How many electrons fit in each shell?
- Maximum in a shell = 2n² (n = shell number).
- K (n=1): 2×1² = 2 ; L (n=2): 2×2² = 8 ; M (n=3): 2×3² = 18 .
- The outermost shell can hold a maximum of 8 (first shell max 2).
- Shells fill inward → outward : K first, then L, then M…
Important Definitions
- Maximum electrons in a shell — given by 2n squared, where n is the shell number; the outermost shell can hold a maximum of 8.
