Chemistry / Unit 5 Chem 0881 short lesson, about 20 seconds
Ionic Radius: Cations
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The idea
A cation is smaller than its parent atom, since removing an electron leaves fewer electrons for the same Zeff to pull inward.
In practice
Aluminum's neutral atom has a larger radius than Al³⁺, since losing three electrons exposes a smaller core to an unshielded pull.
Where people slip
A cation's smaller radius comes from a changed electron-to-proton balance, not from the nucleus losing protons.
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