Chapter 7, Problem 46A

How do positive ions and negative ions form?

Interpretation Introduction

Interpretation:

The formation of positive and negative ions needs to be explained.

Concept introduction:

Most of the atoms does not have eight electron in its valence shells to have a stable configuration. For instance, some may have less than 8 in its outer shell which indicates that it will be deficient of 4 electrons or just 1 to 2 electrons. In case the atom needs less than 3 valence electrons, it will tend to lose those electrons to become electrically neutral and the lower shell electrons will form an octet. Or in some cases, it will gain those 2 electrons and become octet.

Answer to Problem 46A

Atoms will lose electrons to become a positive charged ion and it can gain electrons to become a negatively charged ion so that it attains an octet or stable configuration.

Explanation of Solution

As atoms of elements do not have eight electrons in it valence shells, these atoms will tend to lose or gain electrons to form a stable configuration.

Let us consider Sodium atom that has electronic configuration as ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{1}}$. Here, the valence shell has only 1 electron. There is tendency for this atom to give away this electron as it is far away from the central nuclei which cause the force of attraction between this valence electron and nuclei to be less.

By losing an electron, Sodium atom becomes Sodium ion having an octet structure.

Let us consider Chlorine atom that has electronic configuration as ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^2{\text{3p}}^5$. Here, the valence shell has deficiency of 1 electron to fulfill the condition of octet. Hence, it will take up one electron to become a negatively charged ion.

Conclusion

Atoms will lose electrons to become a positive charged ion and it can gain electrons to become a negatively charged ion so that it attains an octet or stable configuration.