What is the electron configuration of tungsten?

1 Answer
Oct 23, 2017

Tungsten has a regular electronic configuration. Being in period #6# and column #6#, we expect it to have a #d^4# configuration and it sure does.

#[Xe] 5d^4 6s^2#

But unlike what you may think, this IS an exception to the Aufbau Principle. Consider the data from Appendix B.9:

Data from Appendix B.9 of Inorganic Chemistry by Miessler, Fischer, and Tarr

The #6s# orbital of tungsten being slightly above the #5d# orbitals (by about #"0.24 eV"#) makes it so that it is OK for the #6s# electrons to be paired without too much of a loss of stability, even though it goes against the Aufbau Principle to favor pairing an electron in the highest-energy orbital.

The fact that tungsten has this configuration follows from the #5d# and #6s# orbitals being large enough to hold electron density fairly well, which stabilizes the paired electron enough.