Electron arrangement in Nickel [duplicate]








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[Why is the ground state electronic configuration of Group 10 (Ni group) elements so anomalous?](/questions/83170/why-is-the-ground-state-electronic-configuration-of-group-10-ni-group-elements)

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Closed 3 years ago.



I'm struggling to understand why the element Nickel can be written like so: [Ar]3d84s2, but **cannot** be written as [Ar]3d10.


I know that the d-orbital can 'house' 10 electrons, and that according to the Aufbau principle, electrons must be 'housed' in the vacant orbital which has the lowest energy, so the first way I presented seems wrong to me. 


I'm sure that there's some confusion on my end here, or rather, I'm missing something that might seem obvious, but I really don't get it. 




The available energy levels are arranged in the following order, going from the lowest level to the highest :
$1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p,$ etc. So the $4s$ level is filled before the $3d$. 


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