Atomic Radius vs Ionic Radius: What's the Difference?
When sodium hands its electron to chlorine, something dramatic happens to both atoms' waistlines: sodium collapses to nearly half its radius, while chlorine balloons to almost double. One electron, traded between neighbors — and both particles are transformed. If you can explain why, you've understood more about electron structure than most of the class. The short answer: atomic radius is the size of a neutral atom; ionic radius is the size of that atom after it gains or loses electrons. Cations are always smaller than their parent atoms (Na 186 pm → Na⁺ 102 pm), and anions are always larger (Cl ≈ 99 pm → Cl⁻ 181 pm). Quick comparison at a glance Feature Atomic radius Ionic radius Applies to Neutral atoms Ions (charged atoms) Measured from Half the distance between identical bonded/packed nuclei Ion sizes deduced from distances between neighboring ions in crystals Electron count Equals the proton count More (anion) or fewer (cation) than protons ...