Question

Which ion has smallest radius?

Answer 1

Because K+ has the greatest nuclear charge (Z = 19), its radius is smallest, and S2− with Z = 16 has the largest radius. Because selenium is directly below sulfur, we expect the Se2− ion to be even larger than S2−.

Ionic Radii and Isoelectronic Series.

Ion     Radius (pm)           Atomic Number

N3− 146                            7

O2− 140                              8

F−          133                               9

Na+           98                               11

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