Iron(Fe) Electron Configuration and Orbital Diagram
Iron is the 26th element in the periodic table and its symbol is ‘Fe’. In this article, I have discussed in detail how to easily write the complete electron configuration of iron. I also discussed how to draw and write an orbital diagram of iron. Hopefully, after reading this article, you will know more about this topic.
What is the electron configuration of iron?
The total number of electrons in iron is twentysix. These electrons are arranged according to specific rules in different orbitals. The arrangement of electrons in iron in specific rules in different orbits and orbitals is called the electron configuration of iron.
The electron configuration of iron is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{6} 4s^{2}, if the electron arrangement is through orbitals. Electron configuration can be done in two ways.
 Electron configuration through orbit (Bohr principle)
 Electron configuration through orbital (Aufbau principle)
Electron configuration through orbitals follows different principles. For example Aufbau principle, Hund’s principle, and Pauli’s exclusion principle.
Iron atom electron configuration through orbit
Scientist Niels Bohr was the first to give an idea of the atom’s orbit. He provided a model of the atom in 1913. The complete idea of the orbit is given there.
The electrons of the atom revolve around the nucleus in a certain circular path. These circular paths are called orbit(shell). These orbits are expressed by n. [n = 1,2,3,4 . . . The serial number of the orbit]
K is the name of the first orbit, L is the second, M is the third, and N is the name of the fourth orbit. The electron holding capacity of each orbit is 2n^{2}.
Shell Number (n)  Shell Name  Electrons Holding Capacity (2n^{2}) 
1  K  2 
2  L  8 
3  M  18 
4  N  32 
For example,
 n = 1 for K orbit.
The maximum electron holding capacity in K orbit is 2n^{2} = 2 × 1^{2} = 2.  For L orbit, n = 2.
The maximum electron holding capacity in L orbit is 2n^{2} = 2 × 2^{2} = 8.  n=3 for M orbit.
The maximum electrons holding capacity in M orbit is 2n^{2} = 2 × 3^{2 }= 18.  n=4 for N orbit.
The maximum electrons holding capacity in N orbit is 2n^{2} = 2 × 4^{2} = 32.
Therefore, the maximum electron holding capacity in the first shell is two, the second shell is eight and the 3rd shell can have a maximum of eighteen electrons.
The atomic number is the number of electrons in that element. The atomic number of iron is 26. That is, the number of electrons in iron is twentysix. Therefore, the iron atom will have two electrons in the first shell, and eight in the 2nd shell.
According to Bohr’s formula, the third orbit will have sixteen electrons but the third orbit of iron will have fourteen electrons and the remaining two electrons will be in the fourth orbit.
Therefore, the order of the number of electrons in each shell of the iron(Fe) atom is 2, 8, 14, 2. Electrons can be arranged correctly through orbits from elements 1 to 18.
The electron configuration of an element with an atomic number greater than 18 cannot be properly determined according to the Bohr atomic model. The electron configuration of all the elements can be done through the orbital diagram.
Electron configuration of iron through orbital
Atomic energy shells are subdivided into subenergy levels. These subenergy levels are also called orbital. The most probable region of electron rotation around the nucleus is called the orbital.
The subenergy levels depend on the azimuthal quantum number. It is expressed by ‘l’. The value of ‘l’ is from 0 to (n – 1). The subenergy levels are known as s, p, d, and f.
Orbit Number  Value of ‘l’  Number of subshells  Number of orbital  Subshell name  Electrons holding capacity  Electron configuration 
1  0  1  1  1s  2  1s^{2} 
2  0 1  2  1 3  2s 2p  2 6  2s^{2} 2p^{6} 
3  0 1 2  3  1 3 5  3s 3p 3d  2 6 10  3s^{2} 3p^{6} 3d^{10} 
4  0 1 2 3  4  1 3 5 7  4s 4p 4d 4f  2 6 10 14  4s^{2} 4p^{6} 4d^{10} 4f^{14} 
For example,
 If n = 1,
(n – 1) = (1–1) = 0
Therefore, the value of ‘l’ is 0. So, the subenergy level is 1s.  If n = 2,
(n – 1) = (2–1) = 1.
Therefore, the value of ‘l’ is 0, 1. So, the subenergy levels are 2s, and 2p.  If n = 3,
(n – 1) = (3–1) = 2.
Therefore, the value of ‘l’ is 0, 1, 2. So, the subenergy levels are 3s, 3p, and 3d.  If n = 4,
(n – 1) = (4–1) = 3
Therefore, the value of ‘l’ is 0, 1, 2, 3. So, the subenergy levels are 4s, 4p, 4d, and 4f.  If n = 5,
(n – 1) = (n – 5) = 4.
Therefore, l = 0,1,2,3,4. The number of subshells will be 5 but 4s, 4p, 4d, and 4f in these four subshells it is possible to arrange the electrons of all the elements of the periodic table.
Subshell name  Name source  Value of ‘l’  Value of ‘m’ (0 to ± l)  Number of orbital (2l+1)  Electrons holding capacity 2(2l+1) 
s  Sharp  0  0  1  2 
p  Principal  1  −1, 0, +1  3  6 
d  Diffuse  2  −2, −1, 0, +1, +2  5  10 
f  Fundamental  3  −3, −2, −1, 0, +1, +2, +3  7  14 
The orbital number of the ssubshell is one, three in the psubshell, five in the dsubshell and seven in the fsubshell. Each orbital can have a maximum of two electrons.
The subenergy level ‘s’ can hold a maximum of two electrons, ‘p’ can hold a maximum of six electrons, ‘d’ can hold a maximum of ten electrons, and ‘f’ can hold a maximum of fourteen electrons.
Aufbau is a German word, which means building up. The main proponents of this principle are scientists Niels Bohr and Pauli. The Aufbau method is to do electron configuration through the subenergy level.
The Aufbau principle is that the electrons present in the atom will first complete the lowest energy orbital and then gradually continue to complete the higher energy orbital.
The energy of an orbital is calculated from the value of the principal quantum number ‘n’ and the azimuthal quantum number ‘l’. The orbital for which the value of (n + l) is lower is the low energy orbital and the electron will enter that orbital first.
Orbital  Orbit (n)  Azimuthal quantum number (l)  Orbital energy (n + l) 
3d  3  2  5 
4s  4  0  4 
Here, the energy of 4s orbital is less than that of 3d. So, the electron will enter the 4s orbital first and enter the 3d orbital when the 4s orbital is full.
The method of entering electrons into orbitals through the Aufbau principle is 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d.
The first two electrons of iron enter the 1s orbital. The sorbital can have a maximum of two electrons. Therefore, the next two electrons enter the 2s orbital. The porbital can have a maximum of six electrons.
So, the next six electrons enter the 2p orbital. The second orbit is now full. So, the remaining electrons will enter the third orbit. Then two electrons will enter the 3s orbital of the third orbit and the next six electrons will be in the 3p orbital.
The 3p orbital is now full. So, the next two electrons will enter the 4s orbital and the remaining six electrons will enter the 3d orbital. Therefore, the iron full electron configuration will be 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{6} 4s^{2}.
Note: The short electron configuration of iron is [Ar] 3d^{6} 4s^{2}. When writing an electron configuration, you have to write serially.
How to write the orbital diagram for iron?
To create an orbital diagram of an atom, you first need to know Hund’s principle and Pauli’s exclusion principle.
Hund’s principle is that electrons in different orbitals with the same energy would be positioned in such a way that they could be in the unpaired state of maximum number and the spin of the unpaired electrons will be oneway.
And Pauli’s exclusion principle is that the value of four quantum numbers of two electrons in an atom cannot be the same. To write the orbital diagram of iron(Fe), you have to do the electron configuration of iron.
Which has been discussed in detail above. 1s is the closest and lowest energy orbital to the nucleus. Therefore, the electron will first enter the 1s orbital.
According to Hund’s principle, the first electron will enter in the clockwise direction and the next electron will enter the 1s orbital in the anticlockwise direction. The 1s orbital is now filled with two electrons.
Then the next two electrons will enter the 2s orbital just like the 1s orbital. The next three electrons will enter the 2p orbital in the clockwise direction and the next three electrons will enter the 2p orbital in the anticlockwise direction.
Then the next two electrons will enter the 3s orbital just like the 1s orbital and then the next six electrons will enter the 3p orbital just like the 2p orbital. The 3p orbital is now full. So, the next two electrons will enter the 4s orbital just like the 1s orbital.
The 4s orbital is now full. Therefore, the next five electrons will enter the 3d orbital in the clockwise direction and the remaining one electron will enter the 3d orbital in the anticlockwise direction. This is clearly shown in the figure of the orbital diagram of iron.
Iron ion(Fe^{2+}, Fe^{3+}) electron configuration
The ground state electron configuration of iron is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{6} 4s^{2}. This electron configuration shows that the last shell of iron has two electrons and the dorbital has a total of six electrons. Therefore, the valence electrons of iron are eight.
There are two types of iron ions. The iron atoms exhibits Fe^{2+} and Fe^{3+} ions. The iron atom donates two electrons in the 4s orbital to form an iron ion(Fe^{2+}).
Fe – 2e^{–} → Fe^{2+}
Here, the electron configuration of iron ion(Fe^{2+}) is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{6}. The iron atom donates two electrons in 4s orbital and an electron in 3d orbital to convert iron ion(Fe^{3+}).
Fe – 3e^{–} → Fe^{3+}
The electron configuration of iron ion(Fe^{3+}) is 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{6}. Iron atom exhibit +2 and +3 oxidation states. The oxidation state of the element changes depending on the bond formation.
FAQs

What is the symbol for iron?
Ans: The symbol for iron is ‘Fe’.

How many electrons does iron have?
Ans: 26 electrons.

How do you write the full electron configuration for iron?
Ans: 1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{6} 3d^{6} 4s^{2}.

How many valence electrons does iron have?
Ans: Eight valence electrons.

What is the valency of iron?
Ans: The valency of iron is 2, and 3.