Chapter 9, Problem 123A

Interpretation Introduction

Interpretation: Explain why the ionic radii of Groups 1A and 2A are smaller, whereas those of Group 7A are larger than their respective neutral atoms.

Concept Introduction: Ionic radii denote the distance from the center of the nucleus to the outermost shell of electrons in an ion. The elements on the left side of the periodic table form positive ions whereas those on the right side form negative ions.

Answer to Problem 123A

The ionic radii of elements decrease on moving from left to right across the period in the periodic table. So the ionic radii of Groups 1A and 2A are smaller than the ionic radii of Group 7A.

Explanation of Solution

The elements on the left side of the periodic table have electropositive character, so they lose electrons to form cations. Since they give up electrons, their effective nuclear charge increases, and hence their size decreases from that of their neutral atom. While the elements on the right side of the periodic table are electronegative. They tend to accept electrons and form anions. So, their effective nuclear charge decreases, and the size of anions are larger than their respective atoms.