Question

What is electronic configuration of Chromium?
(A) $\left[ {Ar} \right]3{d^6}4{s^0}$
(B) $\left[ {Ar} \right]3{d^5}4{s^1}$
(C) $\left[ {Ar} \right]3{d^4}4{s^2}$
(D) $\left[ {Ar} \right]3{d^3}4{s^2}4{p^1}$

Answer 1

Hint: The process of distributing the electrons of an element in different orbitals is known as electronic configuration. The principles which govern the filling of electrons are Aufbau principle, Pauli exclusion and Hund’s rule.

Complete Step By Step Answer:
According to the Aufbau principle electrons of chromium start filling from the lowest energy orbital and then move gradually towards the higher energy orbital. The order of orbital depending on increasing energy is-
$1s,2s,2p,3s,3p,4s,3d,4p,5s,4d,5p,6s,4f,5d,6p,7s.$
Based on the principle of Pauli exclusion rule each orbital has a maximum capacity of holding two electrons which have opposite spin.
As we know that the $p - $ orbital is composed of three sub-orbitals $\left( {px,py,pz} \right)$ it has a maximum tendency of holding $6$ electrons.
Atomic number of chromium is $24$, so when we start filling the orbitals starting from $1s$ we give two electrons to each orbital and finally get the configuration of chromium as -
$1{s^2},2{s^2},2{p^6},3{s^2},3{p^6},4{s^2},3{d^4}$
As we already know that fully-filled and half-filled orbital are more stable due to low energy state, so one electrons from $4{s^2}$ move to $3{d^4}$ in order to attain stability in configuration due to half-filled $3d$ orbital. So final configuration of chromium becomes:
$1{s^2},2{s^2},2{p^6},3{s^2},3{p^6},4{s^1},3{d^5}$
Noble gas Argon has total $18$ electrons in its orbital so we can also express the configuration of chromium as-
$ \Rightarrow {\left[ {Ar} \right]^{18}}4{s^1}3{d^5}$
Therefore the option $\left( 2 \right)$ is the correct option.

Note:
Chromium is placed at position one in group $6$ elements. Physical properties of chromium include steel-grey in colour, lustrous in nature, hard and brittle. Chromium is used as an anti-corrosive additive in the production of stainless steel.