Exceptions  of Aufbau Principle

There are a few exceptions to the Aufbau Principle which are Chromium and Copper. Their electronic configuration is,

Electronic Configuration of Chromium

The electronic configuration of Chromium according to the Aufbau Principle should be

• Cr(24): [Ar]3d⁴4s²

But the above configuration is not correct because the actual electronic configuration of Chromium(Cr) is,

• Cr(24): [Ar]3d⁵4s¹

The reason for this electronic configuration is that the half-filled d-atomic orbital is more stable than the orbital filled according to the Aufbau Principle.

Electronic Configuration of Copper

The electronic configuration of Copper according to the Aufbau Principle should be,

• Cu(29): [Ar]3d⁹4s²

The above configuration is not correct because the actual electronic configuration of Copper(Cu) is,

• Cu(29): [Ar]3d¹⁰4s¹

The reason for this electronic configuration is that the full-filled d-atomic orbital is more stable than the orbital filled according to the Aufbau Principle.

Read More

• Quantum Numbers
• Shape of Atomic Orbitals
• Atomic Structure

Aufbau Principle is the basic method that tells us how the electrons are filled in the atomic orbital. According to the Aufbau Principle, the filling of the electrons in the ground state of an atom follow a basic pattern. This principle tells us that the electrons in the atomic orbital of any atoms are filled in the ascending order of their energy and for finding the energy of the atomic orbital they follow the “n+l” rule.

In this article, we will learn about Aufbau Principle, Features of the Aufbau Principle, its exceptions and limitations in detail.