Question

Arrange these ions in order of increasing ionic radius: K+, P3– , S2– , Cl– . Increasing radius  A) K+ < Cl– < S2– < P3– D) Cl– < S2– < P3– < K+ B) K+ < P3– < S2– < Cl– E) Cl– < S2– < K+ < P3– C) P3– < S2– < Cl– < K+ Reasoning:

Answer 1

The ionic radius means the distance between nucleus and outer most electron.

The electronic configuration of

K⁺ is 1S² 2S² 2P⁶ 3S² 3P⁶

Cl^- is 1S² 2S² 2P⁶ 3S² 3P⁶

S^2- is 1S² 2S² 2P⁶ 3S² 3P⁶

P^3-is 1S² 2S² 2P⁶ 3S² 3P⁶

All these ions having the same electronic confugration but the charge on ion is 1,-1,-2 and - 3 for K⁺,Cl^-,S^2-,P^3- respectively.Atomic radius decreses from left to right across the periodic table. when an atom loses electron to form a cation ,the lost electron no longer contributes to shielding the other electrons from the charge of the nucleus then the other electrons are stongly attacted towards nucleus there fore the cation having the smaller radius. when the electron is added ,these electrons are repled by other electrons there fore the size of anion is increses.

There fore the P^3- having the large negative charge that means it take more number of electrons which are more repel by other electron,hence it having the largest ionic radius and the K + donate one electron and other electron are strongly attracted towards nucleus hence having small ionic radius.

The correct order is as K⁺ Cl^- S^2- P^3-