Question

What is the unabbreviated electron configuration of iron?

Answer 1

As we know that electronic configuration is the arrangement of electrons in different orbits and in its orbitals. While writing it, a standard notation procedure is followed where the energy level or shell number is written first followed by the subshell and the number of electrons it contains is written in the superscript.

Complete answer:
Let us first understand about the electronic configuration followed by the unabbreviated electronic configuration of iron:-
-As we know that electron configuration of an element tells us about how electrons are distributed in its
atomic orbitals. It follows a standard notation in which all atomic sub shells containing electrons (where the
number of electrons they hold are written in superscript) are placed in a sequence.
-Now let us answer about the electronic configuration of iron:-
The atomic number of iron is = 26.
Number of electrons in first shell = 2 (maximum capacity is 2)
Number of electrons in second shell = 8 (maximum capacity is 8)
Number of electrons in third shell = 18 (maximum capacity is 18)
Now as we know that the first shell has only 1s subshell, so it will be denoted as: $1{{s}^{2}}$.
The second shell has 2s and 2p subshells, so it will be denoted as: $2{{s}^{2}}2{{p}^{6}}$.
The third shell has 3s, 3p and 3d subshells, so it should be filled as: $3{{s}^{2}}3{{p}^{6}}3{{d}^{8}}$but it is not filled in this manner because according to Aufbau’s principle, the electrons should be filled from lower energy level to higher energy level which means 4s should be filled before 3d as energy of 4s is lower than 3d.
So now the filling would be done as: $3{{s}^{2}}3{{p}^{6}}4{{s}^{2}}3{{d}^{6}}$.
-Hence the unabbreviated electron configuration of iron = $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}4{{s}^{2}}3{{d}^{6}}$.

Note:
-As we can see, the standard notation is quite lengthy electron configurations especially in case of elements having a relatively large atomic number. Therefore an abbreviated notation can be used instead of the standard notation in which the sequence of completely filled subshells that correspond to the electronic configuration of a nearest noble gas is replaced with the symbol of that noble gas in square brackets. For iron the abbreviated electron configuration is: $[Ar]3{{s}^{2}}3{{p}^{6}}4{{s}^{2}}3{{d}^{6}}$.