Filling of Orbitals

[gabbymaraziti]

Why is the d-orbital filled before the s-orbital is filled for some atoms? For example, the electron configuration for Silver is [KR] 4d^10 5s^1. Why is the electron configuration not [KR] 4d^9 5s^2?

[Alice Chang 2H]

One of the UA's explained this during the 5-8 PM session on Friday:
If I recall correctly, the idea is that you should be writing electron configurations in the arrangement of increasing energy. The d-orbital has less energy when an electron is placed in the d-orbital, but otherwise, the s-orbital has less energy on its own (when compared to the d-orbital without any electrons).

In this case with silver, the d-orbital borrows an electron from the s-orbital in order to become more stable (due to wanting to be symmetric), so it becomes [Kr]4d^10 5s^1 rather than [KR] 4d^9 5s^2.

Hope this helps!

[Noah Canio 3C]

Since we're on the topic, the commenter above has got the correct explanation.

It's important to note that this scenario, that is, having the d-orbital filled, takes place for all elements within chromium's column and copper's column (silver is underneath copper in the periodic table). In the case of chromium, having a half-filled d-orbital will actually be more stable than having a filled 4s orbital.

[Ar] 3d^5 4s^1.