Which choice lists two elements with ground-state electron configurations that are well known exceptions to the Aufbau principle
A) Cu and C
B) Cr and Cu
C) Cs and Cl
D) Rb and Co
E) Fe and Co

Question

Quizplus · Accepted Answer

The Aufbau principle states that electrons fill the lowest energy levels first before moving to higher energy levels. However, there are some exceptions to this rule, particularly with the d-block elements. Chromium (Cr) and copper (Cu) are two examples of exceptions to the Aufbau principle. The ground-state electron configuration of chromium is [Ar] 3d^5 4s^1, where it has one electron in the 4s orbital and five electrons in the 3d orbital. This is because it is more stable to have a half-filled or fully-filled d-orbital. Similarly, copper has a ground-state electron configuration of [Ar] 3d^10 4s^1, where it has one electron in the 4s orbital and ten electrons in the 3d orbital. This is also due to the stability of a fully-filled d-orbital.

Which Choice Lists Two Elements with Ground-State Electron Configurations That