How come the valance electrons of MO is [KR]5s^1 4d^5 and not
Because of the extra stability associated with a half-filled d-orbital. See here.
Scroll down to about half way where you see 'exchange' in blue; the configuration charts below that should be helpful as well.
PS: Be careful with your notation; the elements MO and KR do not exist, and should be written as Mo and Kr to denote the elements you speak of.
Thank you, Sirus.
That makes sense, but how would I predict such a thing?
All half filled and full filled orbitals have extra stability.So much that the electron from s orbital may go to the inner orbital.check out e config of Cr,Cu etc.
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