Cu+ electron configuration

[105002507]

I am confused on why the electron configuration of Cu is not [Ar]4s^2 3d^9. this is question 3.5 6th edition

[Rachel Yoo 1F]

Since the question is asking for the electron configuration of Cu+ it means that Cu lost an electron. Originally it would be [ar]3d84s2 but the 2 electrons from the 4s shell move to the 3d shell making the electron configuration [Ar]3d10

[Kate_Santoso_4F]

Cu+ would have a total of 28 electrons since you are losing one electron and Cu normally has 29 electrons. Argon is the nearest noble gas to Cu for the shorthand notation. Half filled and fully-filled orbitals are more symmetrical than any other configuration and symmetry leads to greater stability. Therefore, the electron configuration for Cu+ would be: [Ar] 3d^10. Hope this helps!