NEET d and f-Block Elements: Complete Chapter Revision Notes and Questions by PW

Questions from d- and f-block elements often test how well you connect electronic configuration with oxidation states, magnetic behaviour, colour, and chemical reactivity. Remembering individual facts is useful, but understanding the reason behind a trend can help you solve unfamiliar questions.

PW’s d and f-Block Elements Full Chapter One-Shot Video covers important concepts through detailed explanations, a wide range of practice questions, and previous-year questions (PYQs). Use the notes below to revise key trends, reactions, exceptions, and formulas before attempting the questions from the lecture.

f-Block Elements: Important Notes

The f-block contains two series, lanthanoids and actinoids. Both involve the filling of inner f-orbitals and show similarities in their physical and chemical properties.

Lanthanoids

Lanthanoids are associated with Group 3. Lanthanum is not a lanthanoid, but it is studied alongside the series because its properties closely resemble theirs.

Electronic configuration

The important elements showing a 5d electron are lanthanum, cerium, gadolinium, and lutetium.

Physical and magnetic properties

• Lanthanum is a soft, silvery-white metal.

• Lanthanoids tarnish rapidly in air.

• Hardness generally increases with atomic number.

• Samarium is noted for its hardness and high melting point.

• Lanthanoids conduct heat and electricity well.

• Many Ln³⁺ ions are coloured because of f-f transitions. La³⁺ and Lu³⁺ are colourless.

• La³⁺ and Ce⁴⁺ have an f⁰ configuration, while Yb²⁺ and Lu³⁺ have an f¹⁴ configuration.

• Lanthanide ions are generally paramagnetic. Neodymium is particularly paramagnetic because both orbital and spin angular momentum contribute.

The common oxidation state is +3. Unusually low third ionisation enthalpies are associated with the formation of particularly stable electronic configurations.

Reactions and mischmetal

Lanthanoids react with several non-metals and form compounds such as oxides, hydroxides, halides, sulfides, nitrides, and carbides. They also form salts with acids and react with water to release hydrogen.

Mischmetal is an alloy containing approximately 95% lanthanum and 5% iron, along with traces of sulfur, carbon, calcium, and aluminium.

Actinoids

Actinoids form the 5f series and are mostly radioactive. Their chemistry is more complex than that of lanthanoids because of radioactivity and their wider range of oxidation states.

• The series ends with lawrencium, atomic number 103.

• Their electronic configurations involve the 5f orbitals, with possible involvement of 6d and 7s orbitals.

• Thorium and curium are important configuration exceptions. Thorium has two electrons in the 6d orbital.

• Actinoids show oxidation states ranging from +3 to +7.

• Uranium exhibits +6 among the important higher oxidation states discussed in this chapter.

• Earlier actinides generally have longer half-lives than later members.

d-Block Elements

The d-block contains elements in which the d-orbitals are being filled. Their electronic configurations help explain their variable oxidation states, magnetic properties, coloured compounds, and catalytic activity.

Electronic Configuration and Transition Elements

Electronic configuration exceptions are important, particularly among chromium, copper, and several 4d-series elements.

Zinc, cadmium, and mercury are not transition elements because their atoms and common ions do not have partially filled d-orbitals.

Melting Point and Enthalpy of Atomisation

The general melting-point trend presented in the chapter is:

3d < 4d < 5d

Group 11 is an exception. Among the coinage metals, the 3d element has the highest melting point, the 4d element the lowest, and the 5d element an intermediate value.

Enthalpy of atomisation is the energy required to separate a substance into gaseous atoms. It is related to the strength of metallic bonding and generally follows the trend in melting points.

Oxidation States and Stability

D-block elements commonly show multiple oxidation states because the energies of their ns and (n−1)d electrons are relatively close.

• Scandium mainly shows +3.

• Zinc mainly shows +2.

• Manganese exhibits the maximum number of oxidation states in the 3d series.

• Heavier d-block elements generally stabilise higher oxidation states more effectively.

• Chromium in the +6 state acts as an oxidising agent.

• Molybdenum and tungsten also show +6, but this oxidation state is more stable for them.

Chemical reactivity depends on the relative stability of the species involved. When a species acts as an oxidising agent, it accepts electrons and is reduced.

High Oxidation States and Oxide Character

Higher oxidation states generally increase the covalent character and acidic character of metal oxides.

• Lower oxidation-state oxides are generally ionic and basic.

• Higher oxidation-state oxides are generally covalent and acidic.

• Some oxides, including vanadium pentoxide, are amphoteric.

Manganese reaches +7 with oxygen, although it does not form a simple stable halide in the +7 state. Oxygen can stabilise high oxidation states through multiple bonding.

CuI₂ does not exist as a stable compound because Cu²⁺ oxidises iodide ions to iodine and is reduced to Cu⁺.

Magnetic Properties and Colour

Magnetic behaviour and colour are frequently tested in d-block chemistry. Both depend on electronic configuration and the types of electronic transitions possible.

Magnetic Moment

Paramagnetism arises from unpaired electrons. For 3d elements, orbital angular momentum is generally quenched, so spin angular momentum is the main contributor.

The spin-only magnetic moment is:

Magnetic moment = √[n(n + 2)] Bohr magnetons

Here, n represents the number of unpaired electrons.

• d⁰ and d¹⁰ species have no unpaired electrons and are diamagnetic.

• A d⁵ configuration has five unpaired electrons.

• d⁴ and d⁶ configurations have the same number of unpaired electrons in the high-spin comparison discussed.

• A magnetic moment of approximately 4.9 Bohr magnetons indicates five unpaired electrons.

Colour of Transition-Metal Compounds

Transition-metal compounds may be coloured due to electronic transitions.

Some d⁰ compounds are coloured because of charge-transfer transitions. Iron compounds may show colour due to d-d transitions.

Catalytic Properties, Interstitial Compounds and Alloys

Transition metals and their compounds are used as catalysts in several industrial processes. They also form interstitial compounds and alloys because of their metallic properties.

Important Catalysts

• Contact Process: V₂O₅

• Haber Process: Powdered iron

• Hydrogenation: Nickel

• Deacon Process: CuCl₂

• Wilkinson Process: [RhCl(PPh₃)₃]

• Ziegler–Natta Process: Organoaluminium compound and titanium chloride

Wilkinson’s catalyst contains rhodium, chloride, and three triphenylphosphine ligands. The Ziegler-Natta catalyst combines an organoaluminium compound with titanium chloride.

Interstitial Compounds and Alloys

Interstitial compounds form when small atoms occupy spaces within a metal lattice. Their important properties include:

• Non-stoichiometric composition

• Greater hardness than the pure metal

• High melting points

• Chemical inertness

• Metallic electrical conductivity

Common alloys include steel, bronze (copper and tin), and brass (copper and zinc).

Potassium Dichromate and Potassium Permanganate

Potassium dichromate and potassium permanganate are important oxidising agents. Revise their preparation, colour changes, oxidation states, and reactions in different media.

Potassium Dichromate (K₂Cr₂O₇)

Potassium dichromate is prepared from chromite ore through the following steps:

1. Chromite ore is fused with sodium carbonate in air to form yellow sodium chromate.

2. Sodium chromate is acidified to form sodium dichromate.

3. Sodium is exchanged with potassium to obtain orange potassium dichromate.

Chromate-dichromate equilibrium

• Adding H⁺ converts chromate into dichromate.

• Adding OH⁻ converts dichromate into chromate.

• Chromate is yellow, while dichromate is orange.

• Both ions have tetrahedral structures.

In an acidic medium, dichromate reduces chromium from +6 to +3 and acts as an oxidising agent. It oxidises iodide to iodine, Fe²⁺ to Fe³⁺, Sn²⁺ to Sn⁴⁺, and H₂S to sulfur.

Potassium Permanganate (KMnO₄)

Potassium permanganate is prepared by heating manganese dioxide from pyrolusite with KOH and an oxidising agent to form green potassium manganate. Further oxidation produces potassium permanganate.

Permanganate is diamagnetic and intensely coloured due to ligand-to-metal charge transfer. Manganate is paramagnetic.

In acidic medium, permanganate oxidises Fe²⁺ to Fe³⁺, iodide to iodine, nitrite to nitrate, sulfide to sulfate, and H₂S to sulfur. Iodide forms iodine in acidic medium but iodate in neutral or slightly alkaline medium.

Manganate also undergoes disproportionation:

3MnO₄²⁻ → 2MnO₄⁻ + MnO₂

Manganese is simultaneously oxidised from +6 to +7 and reduced from +6 to +4. MnO₂ forms a black precipitate.

d and f-Block Elements: 15 Important Questions for NEET 2027

Practise these objective and subjective questions to revise electronic configurations, oxidation states, magnetic properties, lanthanoids, actinoids, and important redox reactions.

Objective Questions

Q1. Which of the following is not considered a transition element?

A. Iron
B. Chromium
C. Zinc
D. Manganese

Answer: C. Zinc

Q2. What is the most common oxidation state of lanthanoids?

A. +1
B. +2
C. +3
D. +4

Answer: C. +3

Q3. Which of the following ions has an f⁰ configuration?

A. La³⁺
B. Nd³⁺
C. Sm³⁺
D. Gd³⁺

Answer: A. La³⁺

Q4. Which element exhibits the maximum number of oxidation states in the 3d series?

A. Scandium
B. Titanium
C. Manganese
D. Zinc

Answer: C. Manganese

Q5. Which of the following compounds is used as a catalyst in the Contact Process?

A. Fe
B. Ni
C. V₂O₅
D. CuCl₂

Answer: C. V₂O₅

Q6. Which of the following ions is generally colourless because of its d⁰ configuration?

A. Ti⁴⁺
B. Cu²⁺
C. Ni²⁺
D. Co²⁺

Answer: A. Ti⁴⁺

Q7. A species has five unpaired electrons. What is its approximate spin-only magnetic moment?

A. 1.73 BM
B. 2.83 BM
C. 4.90 BM
D. 5.92 BM

Answer: D. 5.92 BM

Q8. What is the colour of the chromate ion, CrO₄²⁻?

A. Orange
B. Yellow
C. Green
D. Purple

Answer: B. Yellow

Q9. What is the oxidation state of manganese in potassium permanganate, KMnO₄?

A. +2
B. +4
C. +6
D. +7

Answer: D. +7

Q10. Which of the following is an example of an alloy of copper and zinc?

A. Bronze
B. Brass
C. Steel
D. Mischmetal

Answer: B. Brass

Subjective Questions

Q11. Why do transition metals show variable oxidation states?

Answer: The energies of the ns and (n−1)d electrons are relatively close. Consequently, different numbers of these electrons can participate in bonding, allowing transition metals to exhibit multiple oxidation states.

Q12. Explain lanthanoid contraction.

Answer: Lanthanide contraction refers to the gradual decrease in atomic and ionic radii across the lanthanoid series as atomic number increases. The increasing nuclear charge is not fully offset by the shielding effect of the added 4f electrons.

Q13. Why are many transition-metal compounds coloured?

Answer: Many transition-metal ions have partially filled d-orbitals. Electrons can absorb energy and undergo d-d transitions, producing colour. Some compounds are coloured due to charge-transfer transitions instead.

Q14. Write the spin-only magnetic moment formula and explain its terms.

Answer: The spin-only magnetic moment is given by:

Magnetic moment = √[n(n + 2)] BM

Here, n is the number of unpaired electrons, and BM stands for Bohr magneton.

Q15. What happens when potassium permanganate reacts in an acidic medium? Give two examples of its oxidising action.

Answer: In acidic medium, permanganate acts as a strong oxidising agent, and manganese is generally reduced from +7 to +2. For example, it oxidises Fe²⁺ to Fe³⁺ and iodide ions to iodine.

The d and f-Block Elements Full Chapter One Shot Video for NEET includes a wide range of questions and PYQs alongside chapter explanations. Use it to practise applying electronic configurations, oxidation-state trends, magnetic moment calculations, colour-based concepts, and redox reactions.

 Revise the d- and f-block elements chapter with PW’s full-chapter one-shot video, important notes, and question practice, including PYQs. Regular practice can help you strengthen your concepts, improve accuracy, and prepare more confidently for NEET 2026.

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