Electron Configurations That Differ from Predicted Configurations

Some of the elements have electron configurations that differ slightly from what our general procedure would lead us to predict. Because a few of these elements are important ones, it is useful to know their actual electron configurations. Six of these are listed on the table below. 

Unusual Electron Configurations

Element Predicted Electron Configuration Actual Electron Configuration
copper, Cu [Ar] 3d9 4s2 [Ar] 3d10 4s1
silver, Ag [Kr] 4d9 5s2 [Kr] 4d10 5s1
gold, Au [Xe] 4f14 5d9 6s2 [Xe] 4f14 5d10 6s1
palladium, Pd [Kr] 4d8 5s2 [Kr] 4d10
chromium, C r [Ar] 3d4 4s2 [Ar] 3d5 4s1
molybdenum, Mo [Kr] 4d4 5s2 [Kr] 4d5 5s1

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