NEET d and f Block Elements Notes and Important Questions by PW

d and f-block elements can be challenging to revise because many questions depend on remembering exceptions to general trends. Electronic configurations, oxidation states, magnetic behaviour, colours and reactions may appear similar across different elements, making it important to understand why these properties vary instead of relying only on memorisation.

PW’s d & f Block in One Shot for NEET brings together important concepts, tricks, Previous Year Questions (PYQs) and multiple-choice questions (MCQs) to support your revision. Use the chapter notes alongside the video to revisit key trends, understand common exceptions and practise applying concepts to NEET-style questions.

Coordination Compounds: Colour And Isomerism

Crystal-Field Splitting And Colour

The spectrochemical series gives the relative strength of ligands.

• Weak ligands produce smaller splitting.

• Strong ligands produce larger splitting.

• Greater splitting means greater absorbed energy and shorter wavelength.

The relation is:

Stronger ligand → larger splitting → higher energy → shorter wavelength

A d-d transition occurs when an electron moves between split d-orbitals. Species with d0 and d10 configurations are colourless through d-d transitions because d-orbitals are either empty or completely filled.

Colour may also arise from charge-transfer transitions. This explains the colour of d0 species such as permanganate and dichromate.

Important Isomerism Types

Memory Tip: Ambidentate ligand means linkage isomerism. Coordination isomerism requires both a complex cation and a complex anion.

Tetrahedral complexes do not show geometrical isomerism because all positions are equivalent. Square-planar complexes can show cis-trans isomerism but do not show optical isomerism because of their plane of symmetry.

In octahedral complexes, the cis form of suitable chelated complexes may be optically active, while the trans form is optically inactive. An octahedral MA3B3 complex shows facial and meridional isomerism:

• Facial: three similar ligands occupy one triangular face.

• Meridional: three similar ligands lie along a meridian.

Key d-Block Properties

Variable Oxidation States

Transition metals show variable oxidation states because the energies of the ns and (n-1)d orbitals are close. Electrons from both subshells can participate in bonding.

Manganese shows the highest oxidation state in the first transition series, reaching +7. Scandium generally shows only +3, while zinc generally shows only +2 and is not considered a transition element because of its d10 configuration.

Magnetic Moment

The number of unpaired electrons determines magnetic behaviour and spin-only magnetic moment:

Magnetic moment = square root of n multiplied by (n + 2) BM

Here, n is the number of unpaired electrons.

For V2+, the configuration is d3. It has three unpaired electrons, so its magnetic moment is the square root of 15 BM.

For d1 to d5, the number of unpaired electrons equals the d-electron count. For d6 to d10:

Unpaired electrons = 10 − d-electron count

More unpaired electrons generally mean a greater magnetic moment and stronger metallic bonding.

Melting Point And Enthalpy Of Atomisation

Metallic bonding is strongest when more unpaired d-electrons participate in interatomic bonding. Therefore, melting point, boiling point, and enthalpy of atomisation generally increase from d1 to d5 and decrease from d6 to d10 as pairing begins.

Zinc, cadmium, and mercury have d10 configurations. They have no unpaired d-electrons, weaker metallic bonding, lower melting points, and soft metallic character.

Packing efficiency can cause deviations from the general trend. Tungsten is associated with the highest melting point in the d-block, while zinc has a particularly low enthalpy of atomisation.

Complex Formation And Catalysis

Transition metals form complexes because they have:

• Small ionic size

• High charge density

• Vacant orbitals

Their catalytic activity mainly results from variable oxidation states and complex formation. The catalyst forms an intermediate complex with reactants, brings them closer, lowers activation energy, and increases the reaction rate.

Examples include:

• Ziegler-Natta catalyst

• Wilkinson’s catalyst

• Palladium catalysts

• Vanadium pentoxide, V2O5

Interstitial Compounds

Small atoms such as carbon, nitrogen, boron, and hydrogen can occupy spaces in a metal lattice. These compounds are generally:

• Non-stoichiometric

• Harder than pure metals

• Higher-melting

• Electrically conductive

• Chemically inert

Important Oxidation And Reduction Trends

Cu+ is unstable in aqueous solution and undergoes disproportionation:

Two Cu+ forms Cu2+ and Cu

Cu2+ is more stable because of its high hydration enthalpy.

Cr2+ acts as a reducing agent because it is oxidised to the stable Cr3+ state. Mn3+ and Co3+ act as oxidising agents because they are readily reduced to more stable lower oxidation states.

For M2+ to M reduction:

• Most 3d metals have negative standard reduction potentials.

• Copper is an important exception.

• Copper cannot liberate hydrogen from dilute acids.

• Manganese, zinc, and nickel can liberate hydrogen from dilute acids.

Higher oxidation states become more stable down a d-block group. Thus, the +6 state is more stable for tungsten and molybdenum than for chromium. Consequently, CrO3 and dichromate are stronger oxidising agents than comparable molybdenum and tungsten compounds.

Permanganate And Dichromate Chemistry

Permanganate Ion

MnO4− contains manganese in the +7 oxidation state. It is:

• Tetrahedral

• d0

• Diamagnetic

• Purple or violet

• Coloured due to charge transfer

In acidic medium, permanganate is reduced to Mn2+. In neutral or mildly basic medium, it is reduced to MnO2.

In alkaline medium, permanganate oxidises iodide to iodate:

I− forms IO3−

Manganate, MnO4 2−, is green, paramagnetic, and contains manganese in the +6 state. It disproportionates in neutral or acidic medium to form permanganate and manganese dioxide.

Preparation Of KMnO4

Pyrolusite ore or MnO2 is first converted to manganate and then oxidised to permanganate. The industrial process uses alkaline conditions followed by electrolytic oxidation.

Dichromate Ion

Cr2O7 2− is:

• Orange

• Stable in acidic medium

• A strong oxidising agent

• Formed from two tetrahedral units joined by a bridging oxygen

Chromate, CrO4 2−, is yellow and stable in basic medium. Acid converts chromate to dichromate, while base converts dichromate to chromate.

Dichromate changes from orange to green when chromium(VI) is reduced to chromium(III). It cannot oxidise chloride ions to chlorine because it is a weaker oxidising agent than chlorine.

Permanganate Titration

Dilute sulfuric acid is used in KMnO4 and ferrous ammonium sulfate titrations.

• Hydrohalic acids are unsuitable because halide ions are oxidised.

• Nitric acid oxidises Fe2+ to Fe3+.

• Concentrated sulfuric acid forms explosive Mn2O7.

• Dilute H2SO4 is suitable.

F-Block Elements

Lanthanides

Lanthanides belong to the sixth period and mainly show the +3 oxidation state. Important exceptions include:

• Eu2+ and Yb2+: reducing agents

• Ce4+ and Tb4+: oxidising agents

Lanthanides are silvery-white metals. Their hardness generally increases across the series. Most trivalent lanthanide ions are coloured, but La3+ and Lu3+ are highlighted as colourless because of f0 and f14 configurations.

Lanthanide Contraction

Lanthanide contraction is the gradual decrease in atomic and ionic radii from lanthanum to lutetium. It occurs because 4f electrons shield the nuclear charge poorly.

The sequence is:

Poor shielding → higher effective nuclear charge → smaller size

It explains the similar sizes and properties of zirconium and hafnium.

Actinides

Actinides are radioactive and mainly show the +3 oxidation state. They show more variable oxidation states than lanthanides and may reach +7.

Actinide contraction is greater than lanthanide contraction because 5f electrons shield less effectively than 4f electrons. However, 5f orbitals participate in bonding more readily because they are less deeply buried.

Important Questions on d and f Block Elements

Practise these five questions based on the chapter notes to revise key concepts and their applications.

Question: Calculate the spin-only magnetic moment of V²⁺ in Bohr magnetons (BM).

Solution: Vanadium (Z = 23) has the configuration [Ar] 3d³ 4s². V²⁺ loses the two 4s electrons, giving [Ar] 3d³, with three unpaired electrons. Using μ = √[n(n + 2)] BM, μ = √[3(3 + 2)] = √15 BM ≈ 3.87 BM.

Answer: √15 BM, approximately 3.87 BM.

Question: Why is MnO₄⁻ coloured even though manganese is in the +7 oxidation state?

Solution: Mn in MnO₄⁻ has a d⁰ configuration, so d-d transitions cannot occur. Its purple colour arises from charge-transfer transitions.

Answer: MnO₄⁻ is purple due to charge-transfer transitions, not d-d transitions.

Question: What causes lanthanide contraction, and why do zirconium and hafnium have similar sizes?

Solution: Lanthanide contraction is the gradual decrease in atomic and ionic radii from lanthanum to lutetium. Poor shielding by 4f electrons increases the effective nuclear charge, pulling electrons closer to the nucleus. This also contributes to the similar sizes of zirconium and hafnium.

Answer: Poor 4f shielding causes lanthanide contraction, contributing to the similar sizes of zirconium and hafnium.

Question: Why does Cr²⁺ act as a reducing agent, while Mn³⁺ acts as an oxidising agent?

Solution: Cr²⁺ readily loses an electron to form Cr³⁺, so it acts as a reducing agent: Cr²⁺ → Cr³⁺ + e⁻. Mn³⁺ gains an electron to form Mn²⁺, which has a stable d⁵ configuration: Mn³⁺ + e⁻ → Mn²⁺. Therefore, Cr²⁺ is a reducing agent, and Mn³⁺ is an oxidising agent.

Answer: Cr²⁺ is readily oxidised to Cr³⁺, while Mn³⁺ is readily reduced to Mn²⁺.

Question: Which acid is suitable for acidifying KMnO₄ during a titration involving ferrous ammonium sulfate, and why are HNO₃ and HCl unsuitable?

Solution: Dilute H₂SO₄ provides the required acidic medium. HCl is unsuitable because chloride ions may be oxidised by KMnO₄, interfering with the titration. HNO₃ can oxidise Fe²⁺ to Fe³⁺ and affect the result. Concentrated H₂SO₄ should also be avoided because it can form explosive Mn₂O₇ under relevant conditions.

Answer: Use dilute H₂SO₄ for KMnO₄ titrations involving ferrous ammonium sulfate.

For more practice, revisit important tricks and strengthen your understanding of d and f block elements with PW’s D & F BLOCK in ONE SHOT | All Concepts, Tricks & PYQs | NEET 2026 video. Review the PYQs and MCQs, then use the worked-out questions to identify concepts that need further revision.

Revising d and f block elements requires a clear understanding of electronic configurations, oxidation states, magnetic properties, colours, reactions and periodic trends. Focus on the exceptions, practise numerical and conceptual questions, and revisit topics you find difficult. PW’s one-shot video covers the important concepts, tricks, PYQs and MCQs to support your Chemistry revision.

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