Chapter 12, Problem 27A

Interpretation Introduction

Interpretation:

The reason for anions to be larger than their parent atoms needs to be explained.

Concept introduction:

Anions are formed by gain of electrons.

Answer to Problem 27A

Anions are larger than their parent atoms because after gaining the electrons, ion has more number of electrons but number of protons remains same. Thus same nuclear charge has to hold more number of electrons. Therefore, effective nuclear charge decreases and the size increase.

Explanation of Solution

Taking example:

  $C{l}^{-}$ is larger than $Cl$

    $C{l}^{-}$    $Cl$

Protons 17  17

Electrons 18  17

Thus, in $C{l}^{-}$ 17 protons are to hold 18 protons. This decreases effective nuclear charge. So size increases.

Conclusion

Thus, anions are always larger than their parent atom.