Gen Chem

[Ibraiz]

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Periodic Table

What is the best way to know which elements are exceptions in period table when it comes to writing their electronic configuration?

For example: Mo is exception with the electronic configuration
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 4d5

Do we have to memorize all the elements with exceptions or there is a way to know which ones have exceptions.

Please advise. Thank you

 

[kpanesar]

so orbitals want to be either full, half full, or empty. so basically anytime you have something that will be 5s2 4d4, it becomes 5s1 4d5 ---> now both orbitals are half full....or if you look at the end of the transition metals such as Cu, normally it would be 5s2 4d9, it becomes 5s1 4d10 ---> now one orbital is half full and another is full.