2A.5 7th edition

[Schem_student]

Question 2A.5 asks for the ground state electron configuration for Cu + which is isolectronic with Ni which would have a configuration of [Ar]3d^8 4s^2 why then is the solution [Ar] 3d^10 ?

[Henri_de_Guzman_3L]

Copper has a "half-filled" 4s subshell. It is a special case. Only 1 electron sits in it's 4s subshell while 10 electrons sit in it's 3d subshell. This is a special case. Therefore, Cu+ is [Ar] 3d^10

[Schem_student]

Thank you ! @Henri_de_Guzman_3L I see that it is more stable as a full 3d orbital so it takes the electron from the 4s. This would then be the same then for Chromium.

[Tony Chung 2I]

Cu and Cr are special cases which means that they have different electron configurations.

[Henri_de_Guzman_3L]

You're welcome! I just learned in discussion today that it is the same case for Ag+ ion which sits right below it on the periodic table. Happy studying!

[Michael Novelo 4G]

Its important to remember that there are two exceptions in the first row of the d block. Cr or Chromium's configuration is [Ar]3d^5 4s^1 and the other exception is Cu or copper which has the configuration [Ar]3d^10 4s^1. I believe one of the TA's mentioned that there are more exceptions further down the periodic table but to just focus on the 1st row of the d block.