QuestionPeriodic properties / ionic radius
Which one of the following is the correct order of ionic radius?
- (a) F⁻ > O²⁻ > Na⁺
- (b) Na⁺ > F⁻ > O²⁻
- (c) H⁻ > H > H⁺
- (d) Al³⁺ > Mg²⁺ > N³⁻
Answer: (c) H⁻ > H > H⁺
Isoelectronic: more negative charge → larger. O²⁻ > F⁻ > Na⁺, and N³⁻ > Mg²⁺ > Al³⁺, so (a), (b), (d) are reversed. H⁻ (1s²) > H (1s¹) > H⁺ (bare proton) → (c). Remember: adding electrons expands the cloud; removing shrinks it.