Electron Configuration of Cu

[Tracy Tran 3L]

Why is the electron configuration of Cu [Ar]4s^1 3d^10 and not [Ar]3d^9 4s^2?

[Chance Lee 1G]

There is a special rule for certain groups in the d-orbital. In particular, the 4th and 9th group (where Cu is) in the d-orbital require one electron from the s orbital to move over to create either 5 electrons or 10 electrons to be in the d-orbital, respectively. In particular, for Cu, the electron configuration would be [Ar] 3d^10 4s^1 since Cu's d-orbital wants to "take" one electron from the 4s orbital, rendering the 4s orbital as one unpaired electron.

[Sristi Palimar 2E]

In his lecture, Dr. Lavelle explained that this was due to symmetry and stability. One might (incorrectly) assume that the electron configuration for copper should be [Ar]3d^9 4s^2. However, because there is an unpaired electron in the 3d subshell, one of the electrons in the 4s subshell moves to the 3d subshell because 3d is at a lower energy level than 4s. Recall that when electrons are at their lowest possible energy level, the atom is considered to be more stable.

[Michelle_Duong_3H]

Hello,

Dr. Lavelle pointed out in lecture that there are a couple of exceptions when it comes to the octet rule and electron configurations. It is more stable for Cu to have a full d subshell than a full s subshell. Thus, one of the electrons that would be in the s subshell instead pairs up with the final unpaired electron in the d subshell.

Hope this helps!

[austinchun]

Hello! In his lecture, Dr. Lavelle mentioned that there were exceptions to some elements in regards to their electron configurations. The most important ones you should remember are Cr and Cu. He explained that it was much more stable when there was a full d subshell rather than a full s subshell. This results in an electron from the s subshell moving the the p subshell. The same thought process can be applied to Cr.

[Sharlene Duong 3E]

The electron configuration of Cu is Cu [Ar]4s^1 3d^10 and not [Ar]3d^9 4s^2 because a completely full d sub-level is more stable than a partially filled d sub-level. So, instead of there being an unpaired electron in the d sub-level, the unpaired electron would be in the 4s orbital. Atoms always want to have the least amount of energy because it makes them more stable, and this configuration would allow more stability. This trend also seen in Silver which is right below Cu on the periodic table.