Hi, I was watching this video: https://www.youtube.com/watch?v=BSYPYLdsbBg. In it, the teacher said the half-filled ECs, molybdenum, and chromium would be different, but she said tungsten's EC wouldn't. Why does this only apply to molybdenum and chromium but not tungsten? I'm a little confused.
- Aditi

Chromium and molybdenum prefer half-filled d-orbitals due to the extra stability from exchange energy and electron correlation effects:

Actual Cr Configuration: Ar 4s¹ 3d⁵
Actual Mo Configuration: Kr 5s¹ 4d⁵
This happens because promoting one s-electron to the d-orbital results in a half-filled, more stable d⁵ configuration, lowering the overall energy.
However in case of W which is heavy element and also have f orbitals as inner shell, screening effect becomes very  poor and 6s orbitals become more stable .So it prefers to have more electron in 6s and hence more low energy for 6s then 5d.

ohh okay thank you, i understand this now. Thanks!