Question

Identify the species having larger radius from the following pairs:

i. Na and Na⁺

ii. Na⁺ and Mg²⁺

Answer 1

i. The nuclear charge is the same in Na and Na⁺. But Na⁺ has a smaller number of electrons and a smaller number of occupied shells (two shells in Na⁺, while three shells in Na). 

Therefore, radius of Na is larger.

ii. Na⁺ and Mg²⁺ are isoelectronic species.

Mg²⁺ has a larger nuclear charge than that of N^a+.

Therefore, N^a+ has larger radius.