# Why do tungsten and chromium have different electronic configurations? [duplicate]

Why is the outer structure of tungsten $\mathrm{5d^46s^2}$ instead of $\mathrm{5d^56s^1}$?

I try to explain this in comparison with outer structure of chromium $\mathrm{4d^55s^1}$ taking into consideration 5d orbitals have lesser energy than 6s orbitals in tungsten by saying that the size of the energy gap between the 3d and 4s orbitals lesser than size of the energy gap between the 5d and 6s orbitals, and the repulsion between electrons in the structure$\mathrm{5d^46s^2}$ more than the repulsion in the structure $\mathrm{5d^56s^1}$ which can push the electron from 5d to 6s to produce the lowest energy structure.

• – Mithoron Feb 22 '18 at 21:07
• Cr is 3d5 4s1, not 4d5 5s1. – orthocresol Feb 22 '18 at 22:50
• @orthocresol thank you i edit and correct the structure of Cr. – Adnan AL-Amleh Feb 23 '18 at 6:48

Firstly note that the energetic differences between $\mathrm d^m\mathrm s^n$ and $\mathrm d^{m-1}\mathrm s^{n+1}$ configurations are generally not large. Sometimes these are not amenable to simple qualitative rationalisation.
• Electron-electron repulsions in the$\mathrm{5d^46s^2}$ structure are larger or lesser than repulsions in the $\mathrm{5d^56s^1}$ structure? – Adnan AL-Amleh Feb 23 '18 at 7:13