Electronic Configuration of Iron - Rules for Filling Electrons in Orbitals, How to prevent iron from rusting and Oxidation states of iron

Which of the few chemical components best promotes our understanding of our planet and its origins, also considered which has had the most impact on human civilization?

Many elements have a huge impact on the human civilization but few of them are the highest impact which changed the way of life of humans e.g- through silver photography is possible, gold is the element that established the international trade, uranium for mass destruction, in same way iron, Since the Industrial Revolution in the 18th century, iron has been the backbone of all industries, and without it, no oil could be produced. One of the reasons life is conceivable on our planet is its strength. Iron makes up the majority of the Earth's core. A magnetic field is created around the Earth when the solid inner core rotates and conversion currents flow through the liquid outer core. This keeps the solar wind at bay, which is a kind of ionizing radiation that is detrimental to living things. Due to the ease with which iron corrodes, the earliest human uses of the metal are difficult to trace, making ancient iron artefacts far rarer than those made of more durable metals such as gold and silver. 

In the shape of iron swords, shields, and spears, iron became a deadly instrument of ancient conflict. the recognition of the industrial iron armoury's strength, a force that would go on to define contemporary international politics and warfare.

Table of contents

• What is electronic configuration?
• Rules for Filling Electrons in Orbitals
• Electronic configuration of iron
• Position in the periodic table 
• Ores of iron
• Rusting of Iron and its prevention
• How to prevent iron from rusting
• Oxidation states of iron:
• Interpretation of the electronic configuration of iron
• Practice problems
• Frequently asked questions - FAQs

What is electronic configuration?

Electrons are filled in orbitals of an element under a set of rules based on the parameters of energy, indistinguishability, and orientation.

You may also want to learn more about electron configuration.

Rules for Filling Electrons in Orbitals

• Aufbau's principle
• Pauli’s exclusion principle
• Hund’s rule for maximum multiplicity

Electronic configuration of iron

The atomic number of iron is 2₆ 

The atomic symbol of iron is Fe

Electronic configuration of Fe₂₆=1s²,2s²2p⁶,3s²3p⁶3d⁶,4s²

Condensed electronic configuration of Fe₂₆=[Ar] 3d⁶,4s²

The atomic mass of Iron is 55.845 u.

Position in the periodic table: 

Iron is a chemical element with the atomic number 26 and the symbol Fe (from Latin: Ferrum). It is a metal that belongs to the periodic table's first transition series and group 8. [Ar] 3d⁶4s² is its electronic configuration. Iron is a transition element.

Ores of iron

• The chief ores of iron are hematite (Fe₂O₃) and magnetite (Fe₃O₄). 
• A mineral is a naturally occurring substance that contains a metal or its compound. An ore is a mineral from which a metal may be profitably mined.
• We can understand in this way, that iron in nature is happy to stay in oxides form like Fe₂O₃ and Fe₃O₄ but for our use, we need it in isolated form (Fe). So, we have to invest a huge amount of money to separate Fe from oxygen through a complex metallurgical process. You must hear about rusting of iron, after a large investment of money, and manpower, the time we separate Fe from its ore but as Fe came in contact with air and mixture it starts rusting.
• The commercial metallurgical process used for extraction of iron: Pyrometallurgy in blast furnace 
• Reducing agent: Coke

Rusting of Iron and its prevention: 

Rusting is one of the transformations that take place in iron items over time, gradually degrading them. Rusting causes enormous financial losses since iron is used to build bridges, ships, autos, truck hulls, and a number of other goods. In fact, excessive moisture concentration in the air hastens corrosion.

The rusting process may be represented by the following equation:

Iron (Fe) + Oxygen (O₂ , from the atmosphere) + water (H₂O) → RUST

How to prevent iron from rusting:

Air, water or both should not come into contact with iron things. One easy approach is to apply a coat of paint or grease. These coatings should be applied on a regular basis to prevent corrosion.

A coating of chromium or zinc can also be used to coat iron. The application of a zinc coating on iron is known as galvanization. The water pipes in our homes are galvanized to keep them from rusting. Electroplating can be done on iron items to make them look more glossy (e.g., shiny) and to prevent corrosion.

Oxidation states of iron:

Iron is frequently found in oxidation states of +2 and +3. Iron (III) compounds are referred to as ferrous, whereas iron (III) complexes are referred to as ferric. Iron (II) compounds are pale green in colour, whereas iron (III) compounds are orange/brown in colour. It can also be found in compounds with a higher oxidation state of +6 such as potassium ferrate (K₂FeO₄).

Interpretation of electronic configuration of iron

• Identification of colour of Fe²⁺ and Fe³⁺ ions 

Compounds generally exhibit colours due to excitation and deexcitation of electrons. In compounds of d block elements colours are produced for mainly 2 reasons

• d-d transition
• Charge transfer

The energy of excitation relates to the frequency of light absorbed when an electron from a lower energy d orbital is pushed to a higher energy d orbital. This frequency is usually in the visible range. The colour seen matches the light absorbed's the complementary colour.

Configuration of Fe²⁺:[Ar]3d⁶

Color of Fe²⁺: Green

Configuration of Fe³⁺:[Ar]3d⁵

Color of Fe²⁺: Yellow

• Magnetic behaviour 

Case 1: if unpaired electrons are presents then, ion exhibits paramagnetic behaviour.

Case 2: if all electrons are fully paired then, the ion exhibits diamagnetic behaviour.

Case 3: if half-filled subshells are present, the ion exhibits ferromagnetic behaviour (d5- extreme case of paramagnetism).

Configuration of Fe²⁺:[Ar]3d⁶

Number of unpaired electrons: 4

Magnetic behaviour: Paramagnetic

A magnetic field attracts paramagnetic material only weakly.

Configuration of Fe³⁺:[Ar]3d⁵

Number of unpaired electrons: 5

Magnetic behaviour: Ferromagnetic

A magnetic field is attracted very strongly by a magnetic field.

• Spin magnetic moment

With the help of electronic configuration we can easily find its spin magnetic moment, 

n=number of unpaired electron

Example 1: Find the spin magnetic moment of Fe²⁺(d⁶ configuration)?

Answer: d⁶configuration :

 number of unpaired electron = 4

• Maximum spin multiplicity:

Maximum spin multiplicity = 2|S|+1 

where, S = total spin 

E.g- for Fe²⁺(d⁶ configuration) 

Maximum spin multiplicity = 2|S|+1 = 2|2|+1=5 

• Exchange energy

Electrons having the same spin and energy present in degenerate orbitals can exchange their positions and in this exchange process, the energy is released and the released energy is termed exchange energy. 

The higher the number of exchanges in a particular configuration, the stability of the configuration becomes higher.

The exchange energy is the basis for Hund's rule, which allows maximum multiplicity, that is electron pairing is possible only when all the degenerate orbitals contain one electron each.

more the number of exchange ∝ more the stability of configuration

maximum number of possible exchange 

Where n is the total number of electrons having same energy and spin

r = 2 (minimum 2 electrons required for exchange)

E.g- for d⁵ configuration 

d⁵ configuration:

Number of electrons having same energy and spin (n) = 5

Minimum number of electrons required for exchange = 2 

maximum number of possible exchange = 

maximum number of possible exchange = 

Practice problems

Q 1. Find the spin magnetic moment of Fe3+(d5 configuration)?

Answer: (B)

d⁵configuration :

 number of unpaired electron = 5

Q 2. Find the maximum possible exchange for Fe2+(d6 configuration)?

a. 12
b. 11
c. 10
d. 15

Answer: (C)

maximum number of possible exchange = 

Where n is the total number of electrons having same energy and spin

r = 2 (minimum 2 electrons required for exchange)

E.g- for d⁶ configuration 

d⁶ configuration:

Case 1: electrons having upward spin

Number of electrons having same energy and spin (n) = 5

Minimum number of electrons required for exchange = 2 

maximum number of possible exchange = 

maximum number of possible exchange =  

Case 2: electrons having downward spin 

Minimum 2 electrons are required for the exchange, so no any exchanges are possible for downward arrow electron.

So, total number of possible exchange = 10 + 0 = 10

Q 3. We know Fe²⁺ show green colour and Fe³⁺ show yellow colour, which will absorb light of highest energy

a. Fe²⁺
b. Fe³⁺
c. Both A and B
d. Can’t be predicted

Answer: (B)

We know, visible colour according to increasing wavelength: VIBGYOR

(Wavelength: Violet > Indigo > Blue > Green > Yellow > Orange > Red)

Wavelength of yellow is smaller than red means frequency of yellow is higher than red.

We know, that if any object's colour is yellow means it reflects yellow and absorbs the complementary colour of yellow.

Complementary colour wheel:

The object's visible colour is yellow means it is absorbed in the zone of violet and the object whose visible colour is green means it absorbed colour in the range of red.

The energy of violet is higher than red.

Q 4. The colour absorbed by Fe²⁺ ions is 

a. Red zone
b. Violet zone
c. Green zone
d. Yellow zone

Answer: (A)

Solution:

We know, that if any object's colour is yellow means it reflects yellow and absorbs the complementary colour of yellow.

Complementary colour wheel:

Fe²⁺ visible colour is green means it absorbed colour in a range of red.

Frequently asked questions-FAQs

Q 1. What is steel?
Answer: Steel is an iron alloy with a few tenths of a per cent of carbon added to increase its strength. Different elements are mixed for the different desired properties.

Chromium (Cr) is mixed for corrosion resistance, heat & oxidation resistant. 

Q 2. What is stainless steel?
Answer: It is a generic term used for a family of corrosion-resistant alloys which contains at least 10.5% chromium. it can also contain other elements. 

Since iron and steel, are the most popular iron alloy, rust in air, corrode in acids, and scale in furnace atmospheres, they are rather poor materials from the perspective of corrosion. Despite this, there is a class of iron-base alloys called stainless steels that are resistant to rust in seawater, corrosion from strong acids, and scaling at temperatures up to 1100 °C.

Q 3. What is the other interpretation of Fe2+(aq)?
Answer: Fe²⁺(aq) can be written as [Fe(H₂O)₆]²⁺

Where Fe acts as a central atom

H₂O^- acts as ligands

Water molecules act as ligands and generally Fe²⁺ ions present in coordination number 6. In complex compounds, coordination numbers are treated as secondary valency and these are directional in nature.

Q 4. What is the maximum perceivable amount of iron in drinking water?
Answer: The maximum permissible amount of iron in drinking water is 2 ppm or 0.2 mg dm-3.

Permissible values of some other ions and elements in drinking water:

Lead: 50 ppb (parts per billion)
Sulphate ion: > 500 ppm.
Nitrate ion: 50 ppm
Manganese: 0.05 ppm
Aluminium: 0.2 ppm
Copper: 3 ppm
Zinc: 5 ppm
Cadmium: 0.05

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