Chapter 5.2, Problem 12LC

Interpretation Introduction

Interpretation: To determine the reason for a different type of electronic configuration of some elements from the Aufbau principle.

Concept Introduction: The placement of electrons inside orbitals around a nucleus is known as electronic configuration, also known as electronic structure, as well as electron configuration.

Answer to Problem 12LC

Half-filled sublevels and filled sublevels are more stable than some other partially filled sublevels, hence some real electron configurations deviate from those predicted by the Aufbau principle.

Explanation of Solution

The Aufbau principle states that as energy levels increase, these electrons must always fill in the order of increasing energy of shells and subshells. The exceptions include elements like copper as well as chromium, whose electrons partially or fill two subshells, some of which are in the greater energy level shells.

The electronic configuration of $\text{Cu}$ is ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{4s}}^{\text{1}}{\text{3d}}^{\text{10}}$ .

The electronic configuration of $\text{Cr}$ is ${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{4s}}^{\text{1}}{\text{3d}}^5$

Half-filled sublevels and filled sublevels are more stable than some other partially filled sublevels.