Chapter 12, Problem 118E

Interpretation Introduction

Interpretation:Trend in electron affinity values from $\text{Al}$ to $\text{Cl}$ as $-44\text{ kJ/mol}$ , $-120\text{ kJ/mol}$ , $-74\text{ kJ/mol}$ , $-200.4\text{ kJ/mol}$ and $-348.7\text{ kJ/mol}$ should be rationalized.

Concept introduction:In order to remove the electron situated in outermost shell certain minimum energy must be imparted to convert an atom to gaseous species. The energy thus imparted represents ionization energy.

The magnitude of ionization energy is determined by how effectively valence electron is held by the nucleus. If the outermost shell has, for instance, one or two electrons that require very minimum ionization energy as they can attain the noble gas configuration upon loss of those electrons.

Reverse of ionization process may result in a gain of one or more electron as exhibited by groups 16 and 17 to attain noble core configuration. These groups have 6 and seven valence electrons and hence favorably accept 2 and 1 electron respectively. This behavior is termed as electron affinity.