Exceptions in Electronic Configuration

Certain elements do not follow the standard rules of electronic configuration due to extra stability gained by half‑filled or fully filled orbitals.  

Key Exceptions  

1. Chromium (Cr)  

   - Expected: [Ar] 3d⁴ 4s²  

   - Actual: [Ar] 3d⁵ 4s¹  

   - Reason: Half‑filled d‑subshell provides extra stability.  

2. Copper (Cu)  

   - Expected: [Ar] 3d⁹ 4s²  

   - Actual: [Ar] 3d¹⁰ 4s¹  

   - Reason: Fully filled d‑subshell is more stable.  

3. Silver (Ag)  

   - Expected: [Kr] 4d⁹ 5s²  

   - Actual: [Kr] 4d¹⁰ 5s¹  

   - Reason: Fully filled d‑subshell stability.  

4. Gold (Au)  

   - Expected: [Xe] 4f¹⁴ 5d⁹ 6s²  

   - Actual: [Xe] 4f¹⁴ 5d¹⁰ 6s¹  

   - Reason: Fully filled d‑subshell stability.  

5. Palladium (Pd)  

   - Expected: [Kr] 4d⁸ 5s²  

   - Actual: [Kr] 4d¹⁰  

   - Reason: Completely filled d‑subshell stability.