Chapter 7.2, Problem 19LC

Interpretation Introduction

Interpretation:The pairs of elements likely to form an ionic compound need to be determined.

Concept Introduction:Ionic compound is formed by the chemical combination of a metal and a non-metal. Here, metal tends to be electron-rich, and non-metal tends to be electron deficient. Thus, metals donate electron/s to form a positively charged ion or cation and non-metals accept electron/s to form a negatively charged ion or anion.

Answer to Problem 19LC

Pairs of elements given in option (c) and (d) are likely to form an ionic compound. The formula forthe ionic compound formed is LiCl and NaI respectively.

Explanation of Solution

Reason for correct option/s:

Considering (c), the given elements are Li and Cl. Here, Li is a metal that belongs to group 1. It has 1 valance electron which can be easily donated to form ${\text{Li}}^{+}$ cation. Similarly, Cl is a non-metal and belongs to group 17. It has 7 valance electrons. It can gain 1 electron to form ${\text{Cl}}^{-}$ ion. Therefore, ${\text{Li}}^{+}$ cation and ${\text{Cl}}^{-}$ anion can chemically combine in a 1:1 ratio to form LiCl.

Considering (d), the given elements are Na and I. Here, Na is a metal belonging to group 1. It has 1 valance electron which can be easily donated to form ${\text{Na}}^{+}$ cation. Similarly, I is a non-metal and belong to group 17. It has 7 valance electrons. It can gain 1 electron to form ${\text{I}}^{-}$ ion. Therefore, ${\text{Na}}^{+}$ cation and ${\text{I}}^{-}$ anion can chemically combine in a 1:1 ratio to form NaI.

Conclusion

Reason for incorrect option/s:

Considering (a), the given elements are Cl and Br. Since both are non-metals, they cannot combine to form an ionic compound.

Considering (b), the given elements are K and He. Here, K is metal but He is a noble gas that is chemically neutral. It can neither gain nor lose electrons because it already has a noble gas electron configuration. An ionic compound can be formed when one element is an electron donor (metal) and the other is an electron acceptor (non-metal).