Question

What is the electron configuration of Cr 3+?

Answer 1

`Cr^(3+):1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)4s^(color(red)(0))3d^(color(red)(3))`

Explanation:

The atomic number of Chromium is `Z=24`, therefore a `Cr` atom possesses `24` electrons.

`Cr:1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)4s^(1)3d^(5)`

Note that it is `4s^(1)3d^(5)` and not `4s^(2)3d^(4)` because a half filled `d` orbital is more stable than a partially filled `d` orbital.

However, the chromium ion `Cr^(3+)` possesses `24e^(-)-3e^(-)=21e^(-)` due to the loss of `3` of its electrons.

Thus, the electron configuration of `Cr^(3+)`is:
`Cr^(3+):1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)4s^(color(red)(0))3d^(color(red)(3))`