Question

Wtite the configuration of cr , z=24. What is the reason for unexpected configuration

Answer 1

EC of Cr = [Ar]3d54s1

ectron orbitals are most stable when they are fully filled or half filled. So the most stable configuration for the 3d subshell is 3d10 or 3d5.

In the case of Chromium, after the 4s2 3d4 configuration is attained, an electron from the 4s orbital jumps to 3d subshell because 3d5 is a much more stable configuration than3d4. That's why final configuration for Chromium is 4s1 3d5

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Answer 2

Configuration of chromium

[Ar] 3d5 4s1

or 1s2 2s2 2p6 3s2 3p6 4s1 3d5.

A completely full or half full d sub-level is more stable than a partially filled d sub-level, so an electron from the 4s orbital is excited and rises to a 3d orbital.