🧪 Electron Configuration Exceptions: Chromium & Copper

🧪 Electron Configuration Exceptions: Chromium & Copper

🔍 Why Do Cr and Cu Have Special Configurations?

Usually, electrons fill orbitals following the Aufbau Principle: from lowest to highest energy. But some elements like Chromium and Copper break this rule slightly to gain **extra stability**.

Chromium (Cr): Instead of [Ar] 4s² 3d⁴, it is [Ar] 4s¹ 3d⁵ – a half-filled d-subshell is more stable.

Copper (Cu): Instead of [Ar] 4s² 3d⁹, it is [Ar] 4s¹ 3d¹⁰ – a full d-subshell gives more stability.

This happens because of:

• Symmetrical orbital arrangement
• Lower electron repulsion
• Exchange energy: more parallel spins = more stability

🧬 Other Elements With Similar Exceptions

• Silver (Ag): [Kr] 5s¹ 4d¹⁰
• Gold (Au): [Xe] 6s¹ 4f¹⁴ 5d¹⁰
• Molybdenum (Mo): [Kr] 5s¹ 4d⁵

🧠 Practice: Which Config Is Correct?

1. What is the correct configuration of Ag (Silver)?

[Kr] 5s² 4d⁹
[Kr] 5s¹ 4d¹⁰
[Kr] 5s² 4d⁸

2. What is the configuration of Mo (Molybdenum)?

[Kr] 5s¹ 4d⁵
[Kr] 5s² 4d⁴
[Kr] 5s² 4d³

3. Why do Cr and Cu show configuration exceptions?

To follow periodic trends
To copy noble gas configs
To gain stability from half/full d-subshells