Why Are Cr, Cu, Rh, and Ir's Electronic Configurations Anomalous?

[lkh1986]

I ony know how to explain the anomality of Cr and Cu's electronic configurations.

And in the assignments, I am asked the following:
(a) For Rh: Why not [Kr]4d7 5s2 but [Kr] 4d8 5s1
(b) For Ir: Why not [Xe]4f14 5d8 6s1 but [Xe] 4f14 5d7 6s2

Can someone give a brief explanation? Thanks.

 

[Gokul43201]

We can help you, but only if you first show us some of your own effort or ideas. Please read the posting guidelines.

Also, we would need to know what class this is for and what topic was last covered in this class (before this problem was posed).