Anomalous Electron Configurations:

Certain atoms appear to violate the orbital-filling rules:

• Chromium's electron configuration is [Ar]4s¹3d⁵ rather than the expected [Ar]4s²3d⁴
   
• Copper's electron configuration is [Ar]4s¹3d¹⁰ rather than the expected [Ar]4s²3d⁹
   
• There are other examples in the heavier d-block and f-block metals.

 

This anomalous behavior occurs when there are enough electrons to produce a half-filled set of degenerate orbitals (as in chromium) or to completely fill a d or f subshell (as in copper).

 

Glass Tubing

Electron Distribution