In this video we go over electron configuration exceptions involving copper and chromium.
There are two main exceptions to electron configuration: chromium and copper. In these cases, a completely full or half full d sub-level is more stable than a partially filled d sub-level, so an electron from the 4s orbital is excited and rises to a 3d orbital.
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https://www.youtube.com/watch?v=Om3QruwD0t8