Question

The electronic configuration of element of atomic number 24 is:
(A) $1s^2$, $2s^2$ , $2p^6$ , $3s^2$ , $3p^6$ , $3d^5$ , $4s^1$
(B) $1s^2$, $2s^2$ , $2p^6$ , $3s^2$ , $3p^6$ , $3d^6$
(C) $1s^2$, $2s^2$ , $2p^6$ , $3s^1$ , $3p^3$ , $3d^{10}$
(D) $1s^2$, $2s^2$ , $2p^6$ , $3s^2$ , $3p^6$ , $3d^4$ , $4s^2$

Answer 1

Hint: Identify the position of the element with the atomic number 24 in the periodic table. Write the electronic configuration such that electrons are filled in increasing order of energy of orbitals. The Aufbau principle can be used as it clearly states the order of energies of the orbitals making it easier to write electronic configuration.

Complete answer:
The element having atomic number 24 can be identified as chromium.
It lies in the group of d-blocks of elements in the periodic table. It is a metal.
We will now write the electronic configuration for the element chromium.
E.C = $1s^2$, $2s^2$ , $2p^6$ , $3s^2$ , $3p^6$ , $3d^5$ , $4s^1$
We see that one electron from the 4s subshell gets transferred to the 3d subshell. This is because it adds stability to the atom due to the half-filled d subshell.
This is in accordance with the Hund's rule of maximum multiplicity.
From the above statements we can conclude that our assumption of electronic configuration is correct.

Therefore, the correct answer is option (A).

Note: Aufbau principle is mainly considered for writing the electronic configuration of elements. However, the electronic configuration of chromium is an exception as explained above. The same exception is seen in the case of copper atoms. Copper has only 1 electron in 4s subshell and has a completely filled 3d subshell which adds stability to the atom.