Chapter 8, Problem 106A

Interpretation Introduction

Interpretation: The ionic radius is to be compared with the atomic radius.

Concept introduction:

An ion is formed by gaining or losing electrons in an atom. The number of electrons lost or gained by an atom becomes its charge. If an element loses electrons, it has a positive charge. In the symbol for an ion, the charge is represented as a superscript of the symbol of the atom for that element.

Explanation of Solution

When an atom loses one or more electrons, a positively charged ion or cation is formed. The cations are smaller in size than the atom from which it is formed. This is because they contain fewer electrons while having the same nuclear charge (no. of protons). The protons in the nucleus are holding the residual electrons more firmly and so, their radii are less than those of the parent atoms.

Thus, cations are shorter in size than their parent atoms.

Anions are formed when an atom gains one or more electrons. Anions are always larger than the parent atom. This is because the number of protons in an atom stays the same, but the number of electrons increases as it forms an anion. The anion's electron cloud spreads and enlarges because of the repulsive force of the electrons becoming stronger than the attraction of the positively charged nucleus.

Thus, anions are larger than their parent atoms.