Chapter 11.4, Problem 2RQ

Interpretation Introduction

Interpretation: The valence electrons and a core electron needs to be differentiated and the valence electron and core electron of an element from ${\text{3}}^{\text{rd}}$ row of periodic table needs to be determined.

Concept introduction: Valence electrons are the electrons that occupy the outermost shell(highest energy level) and core electrons are the electrons occupying the innermost shell(lowest energy level).

Answer to Problem 2RQ

Valence electrons of Magnesium is ${\text{3s}}^{\text{2}}$ and the rest are the core electrons.

Explanation of Solution

Valence electrons are the electrons that occupy the outermost shell and the highest energy level and core electrons are the electrons occupying the innermost shell and lowest energy level.

Let us take magnesium, Mg from the ${\text{3}}^{\text{rd}}$ row periodic table.

Mg have 12 electrons and 12 protons. Therefore, electronic configuration of Magnesium is ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}$

Which can be also written as ${\text{[Ne]3s}}^{\text{2}}$ where Ne represents the electron configuration ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}$

Therefore, the 2 electrons in the 3s orbital are the valence electrons and the rest core electrons.

Conclusion

In finding the valence electron shell configuration first find the nearest noble gas and then write the remaining electrons.