Question

What two factors influence the size of an ion relative to the size of its parent atom?
Would you expect the ionic radius of S2-
to be the same in both MgS and Na2S? Why or
why not?

Answer 1

Two factors that influence the size of ion to size of parent atom are:-

1)Effective nuclear charge:--- the effective nuclear charge depend on number of protons in the nucleus as the number of protons increases the force by which the nucleus attract the electrons also increases and hence size decreases as compared to parent atom and vice versa if protons decreases size also decreases.

2)Shielding effect:---this factor depend on the number of electrons as number of electrons increases the outer electrons are shielded and hence size of ion decreases as compared to  parent atom and vice versa if electrons decreases.

Yes  the ion size of S^2- is  same in MgS and Na2S as in both anion is same that is S^2- .Radii of anion s more than parental atom as number of electron increases so effective nuclear force decreases so size of anion more than parental atom. As the ion S^2- same in both compounds so ionic radii of S^2- same in both MgS and Na2S.