Five ideas in chemical education that must die: Chromium's anomalous configuration
Eric Scerri argues that we may be misleading students about what's behind chromium's anomalous configuraton
The fourth idea in our series is that chromium displays an anomalous configuration – [Ar] 3d5 4s1 – because of the stability of its half-filled sub-shell. Many chemistry textbook authors make this claim. My response is that there is nothing intrinsically stable about half-filled shells or sub-shells and that this is an ad hoc notion that should be abandoned. After all, why should the possession of a half-filled sub-shell confer any additional stability? What principle of physics is supposed to justify such a claim?
As a matter of fact, there is no such justification and it is just another myth that seems to be embraced by many chemical educators. As in the case of my article about the concept of pH 7 being neutral, there is the implication that having a half-filled sub-shell is somehow both necessary and sufficient for an atom to display an anomalous configuration.
Inspired by the book This Idea Must Die Eric Scerri explores outdated chemical concepts, this issue: Chromium's anomalous configuration.
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