Copper and Chromium [ENDORSED]

[veneziaramirez 3I]

What is the exception with Copper and Chromium?

[Jessica Wakefield 1H]

For copper the electron configuration is [Ar] 3d10 4s1. The exception is that the 3d comes before the 4s because the d sub-level is more stable than a partially filled d sub-level.

[Derek Waters 1A]

for Chromium it is still the 3d coming before the 4s as its configuration is [Ar] 3d5 4s1

[altaing]

Why is it more stable?

[Thuy-Anh Bui 1I]

These configurations for copper and chromium are more stable because they result in a more symmetric distribution of the electrons.

For chromium, the electron configuration [Ar]3d5 4s1 distributes the 6 valence electrons evenly. 5 electrons fill the 5 d-orbitals and 1 electron fills the single s-orbital. This distribution is more stable because the electrons are spread out to reduce electron-electron repulsion.

For copper, the electron configuration [Ar]3d10 4s1 fills the d-orbital for stability. These more stable distributions can be seen in the picture below.