D-subshell Electron Configurations

[Audrey Banzali-Marks 1A]

I've been having trouble writing electron configurations with incomplete nd subshells, especially atoms like Cu and Ag. If Ag is the ninth transition metal in the 4d block, how does it have a configuration of [Kr]4d^105s^2? I have the same problem with the configuration for Cu, which looks like the ninth transition metal in the 3d block. Am I missing something when looking at the periodic table?

[Melinda Luo 2G]

I think you may have a small mistake with your configuration; for elements that are in group 11, their (valence) d subshell is 10, but the (valence) p subshell is 1
For example, copper (Cu)'s electron configuration is: [Ar]3d¹⁰4s¹

And for elements in group 6, their (valence) d subshell is 5, but the valence p subshell is 1
For example, chromium (Cr)'s electron configuration is: [Ar]3d⁵4s¹

This exception occurs because it allows the element to achieve a full/half-filled subshell, respectively.

Hope this helps!

[Ashley Johnson 2G]

Copper and Argon are two exceptions. They have a half-filled s level in order to have a full d level, which causes them to be more stable. The half filled and full d sublevels have lower energy than a ful s sublevel.

[AudreyQian1J]

Hello,
Silver has an electron configuration of [Kr] 4d^10 5s^1 because it would be more stable to have the lower energy of the 4d orbital filled. So, instead of having two electrons in the 5s orbital, one of the electrons goes to the 4d orbital to completely fill it up for more stability.
Copper and Chromium are similar - and the main - exceptions from the typical electron configuration. Instead of [Ar] 3d^4 4s^2 for Chromium, the element's electron [Ar] 3d^5 4s^1 so that the 4d orbital is half full and will be more stable. The same concept goes to copper, which has an electron configuration of [Ar] 3d^10 4s^1 instead of [Ar] 3d^9 4s^2, because like silver, a full 4d orbital is more stable.