Question

Write the electronic configuration of chromium (Cr).

Answer 1

Hint: In order to write the electronic configuration of chromium, we have to first know the atomic number of chromium which is $24$. This means that there are $24$ electrons in the chromium atom. We have to understand the orbital arrangement of these electrons around the nucleus.

Complete answer:
The total number of electrons in one chromium atom is $24$ and these electrons are arranged around the nucleus in orbitals with different energy levels.
Now generally one will use the Aufbau principle to write the electronic configuration of an element. If we use this principle to write the electronic configuration of chromium, it would be written as follows.
$1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^2}3{d^4}$

But chromium does not exist in this configuration. It is found that the actual electronic configuration of chromium is given as $1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^1}3{d^5}$
This phenomenon is explained by a concept known as half filled orbital stability. Half filled orbital means that each shell of the orbital consists of one electron and this half filled orbital has been found to be more stable than unfilled or partially filled orbitals.

Hence in chromium, the electron is filled in the d-orbital to complete the half filled orbital configuration instead of pairing with the electron in the s-shell. Therefore we can write the electronic configuration of chromium as $1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^1}3{d^5}$

Note: It is to be noted that the electronic configuration of chromium in terms of noble gas can be written as $\left[ {Ar} \right]3{d^5}4{s^1}$ where Ar is argon. Elements such as Nitrogen also exhibit exceptional electronic configuration since half filled and fully filled orbitals are more stable than partially filled orbitals.