Arrange the following ions in order of increasing ionic radius. a. sulfide ion
b. calcium ion
c. phosphide ion
d. potassium ion

Ca 2+ <K  +  <Ar<Cl  −  <S  2−

Explanation:

Ar,K  + ,Cl  − ,S  2− ,Ca  2+

 have the same number of electrons. Their radii would be different because of their different nuclear charges. The cation with the greater positive charge will have a smaller radius because of the greater attraction of the electrons to the nucleus. Anion with the greater negative charge will have the larger radius. In this case, the net repulsion of the electrons will outweigh the nuclear charge and the ion will expand in size. Hence the correct order will be Ca  

2+  <K +  <Ar<Cl  −  <S  2−