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So Dr. Lavelle was talking about how K and Ca are unique in that the 4s2 orbitals fill before the 3d orbitals, but that this doesn't apply after element 20 (Calcium). Can anyone explain this? I'm a bit confused on why it works this way, and why this only occurs before element 20.
Potassium and Calcium are in the s block of the periodic table and come before the 3d block, therefore K would have the configuration: [AR]4s^1. Calcium would have the configuration [Ar] 4s^2. After element 20, you get into the 3d block, so you would have to put 3d^n (n being 1-10) before the 4s energy level, as it is of lower energy.
Thanks for the response! I understand this, but something else has been bothering me. Why does this only occur in the 4s and 3d orbitals and not afterwards? What exactly happens between the 4d and 5s orbitals, for instance? I know that we are only concerned with elements up to the 1st d-block, but I still feel like this question sort of confuses me conceptually.
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