Anomalous electron configurations
Some atoms, such as some transition metals and some elements in the lanthanide and actinide series, do not adhere strictly to Hund’s rule and Pauli’s principle. The reason the anomalies are observed is the unusual stability of both half-filled and completely filled subshells This behavior can be explained with an example of the chromium atom. Using Hund’s rule and Pauli’s principle, you can write the expected electron configuration of the Cr atom that strictly follows these rules as 1 2 2p 3s²3p 4s 3d However, by moving an electron from the 4s orbital to the 3d orbital you obtain a half-filled 3d orbital. This half-filled orbital is more stable than the combination of the filled 4 orbital and the partially filled 3d orbital. Thus, the observed electron configuration of the Cr atom is 1 2 2p 3s2 3p 4s 3d
Part D
Mo has an anomalous electron configuration. Write the observed electron configuration of Mo
Express your answer in complete form in order of increasing orbital energy. For example, 1s22s2 should be entered as 1s^22s 2.
The Correct Answer and Explanation is :
The observed electron configuration of Molybdenum (Mo) is:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁵
Explanation (300 Words)
Molybdenum (Mo), with an atomic number of 42, belongs to the transition metals and exhibits an anomalous electron configuration similar to chromium (Cr). The expected electron configuration based on Hund’s rule and the Aufbau principle would be:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d⁴
However, the observed electron configuration differs because a more stable arrangement is achieved by shifting one electron from the 5s orbital to the 4d orbital. This results in:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹ 4d⁵
Why Does This Happen?
- Enhanced Stability of Half-Filled Orbitals:
- A half-filled d subshell (4d⁵) is more stable due to the symmetrical distribution of electrons.
- This results in lower repulsion and a more balanced exchange energy.
- Exchange Energy Contribution:
- Electrons in degenerate (same-energy) orbitals exchange positions, leading to exchange energy.
- More unpaired electrons mean higher exchange energy, stabilizing the configuration.
- Relativistic Effects:
- In heavier elements like Mo, relativistic effects influence electron behavior, making the 4d and 5s orbitals closer in energy.
- Thus, an electron can be promoted from 5s to 4d to attain stability.
Conclusion
The anomalous electron configuration of Mo arises due to the stabilization of a half-filled 4d subshell, making 5s¹ 4d⁵ a more favorable arrangement than 5s² 4d⁴. This is a common trend among transition metals, where d-electron stability plays a crucial role in determining the final electron distribution.
Now, I’ll generate an image representing the electron configuration of Mo.
Here is an artistic visualization of the electron configuration of the Molybdenum (Mo) atom, highlighting its anomalous electron arrangement with a half-filled 4d subshell. Let me know if you need any modifications!