Electronic Configuration of Iron - Definition, Structure, Application & Uses

Electronic Configuration of Iron (Fe)

Iron (Fe) is a transition metal with atomic number 26, meaning it contains 26 electrons. Its electronic configuration in the ground state is $[\mathrm{Ar}] \mathrm{3d}^6 \mathrm{4s}^2$, where the first 18 electrons correspond to the noble gas argon, and the remaining eight electrons occupy the 4s and 3d orbitals. According to the Aufbau principle, the 4s orbital is filled before the 3d orbital, resulting in a complete electronic configuration of $1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 4 s^2 3 d^6$. The presence of partially filled 3d orbitals gives iron its characteristic transition metal properties, such as variable oxidation states, formation of complexes, and magnetic behavior. When iron forms ions, electrons are removed first from the 4s orbital; thus, the ferrous ion $\left(\mathrm{Fe}^{2+}\right)$ has the configuration $[\mathrm{Ar}] 3 \mathrm{~d}^6$, while the ferric ion $\left(\mathrm{Fe}^{3+}\right)$ has the more stable half-filled configuration $[\mathrm{Ar}] 3 \mathrm{~d}^5$.

Using Only the Periodic Table

1. Locate iron (Fe) in the periodic table.

2. Iron is in:

   • Period = 4

   • Group = 8

   • d-block (transition metal)

3. Fill electrons according to the position in the periodic table:

   • Up to Argon (Ar, Z = 18) → [Ar]

   • Remaining electrons = 26 − 18 = 8

4. In the 4th period:

   • 4s orbital fills before 3d

   • Electrons fill as 4s², then 3d⁶

Electronic Configuration (Periodic Table Method):

$\mathrm{Fe}=[\mathrm{Ar}] 3 d^6 4 s^2$

Using the Electron Configuration Chart (Aufbau Principle)

According to the Aufbau principle, electrons fill orbitals in increasing order of energy:

Order of Filling:

$1 s \rightarrow 2 s \rightarrow 2 p \rightarrow 3 s \rightarrow 3 p \rightarrow 4 s \rightarrow 3 d$

Electronic Configuration (Aufbau Chart Method):

$1 s^2 2 s^2 2 p^6 3 s^2 3 p^6 4 s^2 3 d^6$

Number of Electrons in Iron

Atomic mass - 55.845

Number of Protons - 26

Number of Neutrons- 30

Number of Electrons- 26

Related Topics link

• Periodic Table Elements
• 118 elements, their symbols and their atomic numbers
• Rutherfords Model of Atoms and Its Limitations
• Reactivity series
• First 20 Elements

Calculate the Oxidation number for $\mathrm{FeSO}_4$

The oxidation number of FeSO₄ is calculated as 0, which is a neutral compound.

The first step is to identify the oxidation rate for each element present in the compound.

The oxidation number of S is 6.

The oxidation number of Fe is +2.

The oxidation number O is (-2 ✕ 4) = - 8

When the entire oxidation number of the conference is included, it provides

(+2) + (+6) + (-8) = 0

(+8) - 8 = 0.

Related Topics link

• Electronic Configuration of First 30 Elements
• Electron Gain Enthalpy
• Homologous Series
• Atomic radius in periodic table in basic chemistry
• Classification of Elements in Modern Periodic Table

Uses of Iron

It is used to make metal and is also used in civil engineering such as reinforced concrete, girders etc.

Iron is used to make alloy metals such as carbon steel with additives such as nickel, chromium, vanadium, tungsten, and manganese.

These are used to make bridges, electric poles, bicycle chains, cutting tools, and gun barrels.

Iron ore contains 3-5% of carbon. It is used for making valves,pumps and pipes

Metal elements are used in Haber's process of producing ammonia.

Magnets can be made up of iron metal and its alloys and compounds.

Some Facts About Iron

1.The normal human body contains about 4 grams of iron in the form of hemoglobin, in the blood.

2.It is the sixth most common thing in the universe.

3.There are four known allotropic metals.

Also read -

Some Solved Examples

Question 1: The correct ground-state electronic configuration of iron ( $Z=26$ ) is:
A. $[\mathrm{Ar}] 3 \mathrm{~d}^8 4 \mathrm{~s}^0$
B. $[\mathrm{Ar}] 3 \mathrm{~d}^6 4 \mathrm{~s}^2$
C. $[\mathrm{Ar}] 3 \mathrm{~d}^7 4 \mathrm{~s}^1$
D. $[\mathrm{Ar}] 3 \mathrm{~d}^5 4 \mathrm{~s}^3$

Solution:

According to the Aufbau principle, electrons fill the 4 s orbital before the 3 d orbital. Iron has 26 electrons, so after $[\mathrm{Ar}]$ ( 18 electrons), the remaining 8 electrons fill as $4 s^2 3 d^6$.

$$
\mathrm{Fe}=[\mathrm{Ar}] 3 d^6 4 s^2
$$

Hence, the correct answer is option (C)

Question 2:The electronic configuration of the ferric ion $\left(\mathrm{Fe}^{3+}\right)$ is:
A. $[\mathrm{Ar}] 3 \mathrm{~d}^6$
B. $[\mathrm{Ar}] 3 \mathrm{~d}^4$
C. $[\mathrm{Ar}] 3 \mathrm{~d}^5$
D. $[\mathrm{Ar}] 4 \mathrm{~s}^1 3 \mathrm{~d}^4$

Solution:

Electrons are removed first from the 4s orbital.

$\begin{aligned}
& \mathrm{Fe} \rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^6 4 \mathrm{~s}^2 \\
& \mathrm{Fe}^{2+} \rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^6 \\
& \mathrm{Fe}^{3+} \rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^5
\end{aligned}$

Hence, the correct answer is option (C)

Question 3: Which of the following statements about iron is correct?

A. Iron has completely filled d-orbitals
B. Iron has half-filled d-orbitals in its ground state
C. Iron shows variable oxidation states due to partially filled d-orbitals
D. Iron does not form complexes

Solution:

Iron has partially filled 3d orbitals $\left(3 d^6\right)$, which allow it to lose different numbers of electrons and form complexes, resulting in variable oxidation states.

Hence, the correct answer is option (C)

Question 4: The number of unpaired electrons in a free iron atom is:

A. 2
B. 3
C. 4
D. 6

Solution:

Electronic configuration of $\mathrm{Fe}:[\mathrm{Ar}] 3 \mathrm{~d}^6 4 \mathrm{~s}^2$
Accordina to Hund's rule. $3 d^6$ has 4 unbaired electrons.

Hence, the correct answer is option (C)