Why Chromium has [Ar] 3d5 4s1 and Copper has [Ar] 3d10 4s1?

2 Answers
Oct 19, 2017

I can give you a summary, but you need to read these links...


Chromium is explained in great detail here

It boils down to an increase in exchange energy and decrease in repulsion energy being enough that the #3d# orbitals are lower in energy than the #4s#, but not so low that #"Cr"# can afford to pair one of its electrons up with a #3d# electron.

Copper is explained over here.

This is easy enough: the #3d# orbitals of #"Cu"# are significantly lower in energy than the #4s# orbitals of #"Cu"#, so electron pairing in the #3d# orbitals is more favorable than in the #4s# orbital.

These configurations give Cr and Cu better stability than what the electron configurations predicted by the Aufbau principle would.

Explanation:

There is a more detailed explanation of this here.

Hope this helps!