Answer to Question #242515 in General Chemistry for dee

Question

Consider the Mg2+ , Cl- , K+ and Se2- ions. Discuss the variation in the ionic size

Answer 1

The ionic radius is the distance between the center of the nucleus and valence electrons of that ion. Ionic radius decreases as the nuclear charge increases.

The atomic number of Mg²⁺ , Cl^- , K⁺ and Se^2- are 12, 19, 17 and 34 respectively.

Mg²⁺ is placed in third period and K⁺ is placed in the fourth period. As we go down in any group ionic size increases as the nuclear distance from the valence electrons increases due to introduction of new shell. So size of Mg²⁺ is less than size of K⁺.

As K⁺ and Cl^- are isoelectronic ions, in case of such ions ionic radius decreases as the nuclear charge increases. Therefore, the size of K⁺ is less than size of Cl^-.

Now Cl^-,is placed in third period and Se^2- is placed in the fourth period.

Therefore size of Cl^- is less than Se^2-.

Thus the increasing order of size is

Mg²⁺ < K⁺ < Cl^- < Se^2-.

Therefore, the first sphere is of Mg²⁺, the second one is of K⁺ third one is of Cl^- and the last one is of Se^2-.