Question

Which of the following element do not follow Aufbau principle?

Options

• Cu and Cr 

• Co and Cr 

• Zn and Cu

• C and Mn

Answer 1

Cu and Cr

Explanation:

The 3d-orbitals of Cr and Cu have half-filled and completely filled electronic configuration respectively which are the most stable electronic configurations: Thus, these both elements do not follow Aufbau principle according to which 4s orbital should be filled first with 2 electrons as it have lower energy than 3d-orbital. So, their electronic configuration are

Cr(Z = 24) = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹

Cu(Z = 29) = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹