The electron configuration for chromium is **NOT** #1s^2 2s^2 2p^6 3s^2 3p^6 3d^4 4s^2#, but #color(blue)(1s^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^1)#.

Interestingly enough, Tungsten is much more stable v an electron setup of #

Unfortunately, over there is no easy way to describe these deviations in the ideal order because that each element.

To describe *Chromium*"s electron configuration, we might introduce:

**exchange energy**#Pi_e# (a stability quantum mechanical element that is directly proportional to the variety of pairs of electron in the exact same subshell or an extremely close-energy subshells through parallel spins)The

**coulombic repulsion energy**#Pi_c# (a destabilizing variable that is inversely proportional come the number of electron pairs)These incorporate to create an in its entirety

**pairing energy**#Pi = Pi_c + Pi_e#.

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The previous is stabilizing and the latter is destabilizing, together shown listed below (suppose configuration **2** is at pairing power #Pi = 0#):

One explanation for Chromium, then, is that:

The*maximized*

**exchange energy**#Pi_e# stabilizes this configuration (#3d^5 4s^1#). The maximization comes from how there space #5# unpaired electrons, rather of just #4# (#3d^4 4s^2#).The

*minimized*

**coulombic repulsion energy**#Pi_c# more stabilizes this configuration. The minimization comes from having every unpaired electron in the #3d# and also #4s# (#3d^5 4s^1#), rather than one electron pair in the #4s# (#3d^4 4s^2#).The

**small-enough orbital size**way that the electron thickness is

*not as spread out as it*, which makes it favorable

**could**be*enough*for a maximum total spin to give the many stable configuration.

However, *Tungsten*"s #5d# and #6s# orbitals being bigger than the #3d# and #4s# orbitals (respectively) spreads the end the electron density enough the the pairing power (#Pi = Pi_c + Pi_e#) is small enough.

The more the electron circulation is spread out out, the less electron-pair repulsion over there is, and thus the lower #Pi_c# is. Therefore, the lower #Pi# is.

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Thus, electron pairing is favorable *enough* for Tungsten.

*There is no hard and also fast preeminence for this, however that is an explanation the correlates with speculative data.*