# How do you determine the electron configuration of Fe?

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Hint: The electron configuration of Fe can be determined by the Aufbau principle, which basically gives us the idea of subshells in which electrons are present. And also tells us about the energies and shape of that subshells.

Complete Solution :
- As we know that iron is a transition metal. It basically follows the Aufbau principle of the filling of the atomic orbitals.
- It is found that the atomic number of iron is 26. This means that its atoms contain 26 protons in their nuclei. And if neutral then 26 electrons in their electron clouds.
As we know that the shell value is denoted by the principal quantum number (n). K = 1, L = 2, M = 3, N = 4, O = 5.
- The electronic configuration of Fe is:
$1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}3{{d}^{6}}4{{s}^{2}}$
- From the electronic configuration it was observed that,
K shell contains 2 total electrons ($1{{s}^{2}}$)
L shell contains 8 total electrons ($2{{s}^{2}}2{{p}^{6}}$)
M shell contains 8 total electrons ($3{{s}^{2}}3{{p}^{6}}$)
N shell contains 8 total electrons ($3{{d}^{6}}4{{s}^{2}}$)
- As we know that 4s sublevel fills before the 3d sublevel because it has lower energy. We can say that the electronic configuration lists the sublevels of each energy level, even if the 4s sublevel has lower energy than that of the 3d sublevel.

Note: It should be noted that we might get confused with the idea of a half filled and partially filled orbital. Basically, it is found that half filled d orbital contains only five electrons, whereas partially filled d orbital can have anywhere in between one to nine electrons in them, but it is not fully occupied.