Class 12 Chemistry Ch 4 d and f Block Elements Notes PDF

Class 12 Chemistry Chapter 4 The d- and f-Block Elements is one of the most heavily tested inorganic chapters in JEE Main and NEET, with at least one direct question on lanthanoid contraction, KMnO₄ preparation or magnetic moment appearing in almost every shift since 2021. This revision page hosts the 26-page Notes PDF, the sub-topic weightage map, oxidation-state ladders and the latest CBSE PYQ trends. Treat these d and f block elements class 12 notes as the canonical revision asset for the 2026-27 syllabus.

• CBSE Boards: 4 to 6 marks every year, typically one 3-mark conceptual question on lanthanoid contraction or KMnO₄, plus one assertion-reason MCQ on transition metal colour or magnetic behaviour.
• JEE Main: 2 to 3% of the Chemistry paper, with one or two questions per shift on electronic configurations of Cr and Cu, magnetic moment, and oxidation states of 3d series.
• NEET: 2 to 3 questions per year, almost always from lanthanoid contraction, spin-only formula, or KMnO₄ and K₂Cr₂O₇ chemistry.

The notes below build the chapter the way examiners actually mark it: position in the periodic table first, then the anomalous electronic configurations of Cr and Cu, then the four headline trends (atomic radii, ionisation enthalpy, oxidation states, magnetic behaviour), and finally lanthanoid contraction with KMnO₄ and K₂Cr₂O₇ preparation as the inorganic anchors.

These Collegedunia d- and f-Block Elements notes are curated by subject experts, mapped to the 2026-27 NCERT print, and refined against the last five years of CBSE Board, JEE Main, and NEET papers.

Also Check:

• The d- and f-Block Elements Class 12 Chemistry NCERT Solutions
• The d- and f-Block Elements Class 12 Chemistry Formula Sheet
• CBSE Class 12 Chemistry Syllabus 2026-27

Why d- and f-Block Elements Matter for CBSE, JEE and NEET

This is the chapter where descriptive inorganic chemistry meets pattern recognition. Transition metals occupy groups 3 to 12 of the periodic table, where the last electron enters the (n-1)d sub-shell while the ns orbital is already filled. That single structural fact explains why these elements show variable oxidation states, paramagnetism, intense colour, and catalytic activity, the four properties CBSE and NEET ask about year after year.

The f-block runs parallel: lanthanoids (4f) and actinoids (5f) show similar shrinkage in radii, but actinoids show many more oxidation states because their 5f, 6d and 7s levels are close in energy. The chapter therefore rewards memorising trends, not formulae.

The D and F Block Elements Video Walkthrough

Source: Magnet Brains on YouTube

How will Collegedunia's NCERT Notes Help You with The d- and f-Block Elements?

These notes are written by inorganic-chemistry specialists who have decoded the last five years of CBSE marking schemes and the 2024 and 2025 JEE Main shift papers, so what you read here is what gets ticked on the answer sheet.

• 2026-27 NCERT Alignment: Every topic matches the current 2026-27 syllabus, including the trimmed sections on inner transition elements and the retained KMnO₄ and K₂Cr₂O₇ preparation.
• Trend Tables, Not Walls of Text: Atomic radii, ionisation enthalpy and oxidation-state ladders are presented as one-glance tables, because that is how the chapter is revised in 24 hours.
• Expert Verification: Subject experts have re-checked every electronic configuration, oxidation state and equation against the latest NCERT textbook print.
• Reasoning Anchors: Each property ends with the one-line reason CBSE markers reward, marked in yellow for last-minute recall.

Most Important Sub-Topics in The d- and f-Block Elements and Their Mark Distribution

An audit of CBSE, JEE Main and NEET papers from 2021 to 2025 shows the chapter's marks concentrate on a tight set of sub-topics. The table below ranks them by frequency of appearance so revision time can be apportioned correctly.

The d- and f-Block Elements Topic-by-Topic Notes for Class 12 Chemistry

Position and configuration set up trends, trends explain colour and magnetism, and colour and magnetism culminate in the lanthanoid story. Each H3 below follows that order.

Position in the Periodic Table and General Electronic Configuration

The d-block occupies groups 3 to 12 of the modern periodic table and contains four transition series: 3d (Sc to Zn), 4d (Y to Cd), 5d (La and Hf to Hg), and 6d (Ac, Rf onwards). The general outer electronic configuration is (n-1)d^1-10 ns^0-2 . Chromium (Z = 24) shows the anomalous [Ar] 3d⁵ 4s¹ and Copper (Z = 29) shows [Ar] 3d¹⁰ 4s¹ because half-filled and fully filled d-orbitals are extra stable due to symmetrical distribution and exchange energy.

Atomic and Ionic Radii Trend Across the 3d Series

Across a period, atomic radius first decreases (Sc to Cr), then remains nearly constant (Cr to Cu) and finally increases slightly at Zn. The early decrease is due to increasing nuclear charge; the middle plateau is because additional d-electrons screen the nuclear charge effectively; the rise at Zn comes from electron-electron repulsion in the filled 3d¹⁰ shell. Comparing 4d and 5d, the radii are almost identical due to lanthanoid contraction.

Ionisation Enthalpy, Oxidation States and Standard Electrode Potentials

Ionisation enthalpy generally increases across each series but with irregularities at d⁵ and d¹⁰ configurations. Variable oxidation states are the headline property: Mn shows the widest range (+2 to +7), Fe shows +2 and +3, while the highest oxidation state for any 3d element is +7 in Mn. Standard reduction potentials E^∘(M²⁺/M) show a general trend of becoming less negative across the period, but Mn, Ni and Zn are exceptions, explained by sublimation, ionisation, and hydration enthalpy combinations.

Magnetic Properties and the Spin-Only Formula

Most transition metal ions are paramagnetic because of unpaired d-electrons. The spin-only magnetic moment is given by μ = √n(n+2) BM, where n is the number of unpaired electrons. For example, Mn²⁺ ( 3d⁵ , n = 5 ) gives μ = √35 ≈ 5.92 BM, the maximum for any 3d ion. Diamagnetic ions like Zn²⁺ ( 3d¹⁰ ) have n = 0 and μ = 0 .

Colour, Catalysis and Interstitial Compounds

Transition metal ions are coloured because of d-d transitions: an electron absorbs visible-light energy and jumps from one d-orbital to another of slightly higher energy. The colour observed is complementary to the absorbed wavelength. Ions with d⁰ (Sc³⁺, Ti⁴⁺) or d¹⁰ (Zn²⁺, Cu⁺) are colourless. The same partially filled d-orbitals make transition metals excellent catalysts: V₂O₅ in the Contact process, Fe in the Haber process, Ni in hydrogenation, and Pt in catalytic converters. Their ability to trap small atoms (H, C, N, B) in lattice voids gives rise to interstitial compounds, which are hard, high-melting and chemically inert.

Preparation and Properties of KMnO₄ and K₂Cr₂O₇

Both compounds are CBSE staples and demand precise equations. KMnO₄ is prepared from pyrolusite (MnO₂) by fusion with KOH in air, oxidation to K₂MnO₄, then electrolytic or chemical oxidation to KMnO₄. It acts as a strong oxidising agent in acidic medium: MnO₄^- + 8H⁺ + 5e^- → Mn²⁺ + 4H₂O . K₂Cr₂O₇ is prepared from chromite ore (FeCr₂O₄) via fusion with Na₂CO₃ in air; it oxidises Fe²⁺ to Fe³⁺ and I^- to I₂ in acidic medium.

The Lanthanoids, Lanthanoid Contraction and Its Consequences

The 14 lanthanoids (Ce to Lu) show a steady decrease in atomic and ionic radii from La³⁺ to Lu³⁺, called lanthanoid contraction. The cause is poor shielding by 4f electrons, so the effective nuclear charge experienced by outer electrons rises across the series. Its three exam-mandatory consequences are: (i) nearly identical sizes of 4d and 5d transition metals (Zr/Hf, Nb/Ta), (ii) difficulty in separating individual lanthanoids, and (iii) basicity decreases from La(OH)₃ to Lu(OH)₃. The common oxidation state is +3, with Ce(+4), Eu(+2), and Yb(+2) as standard exceptions.

The Actinoids and a Quick Comparison with Lanthanoids

The 14 actinoids (Th to Lr) show actinoid contraction too, but more pronounced than lanthanoid contraction because 5f electrons shield even less effectively than 4f. Unlike lanthanoids, actinoids show many more oxidation states (up to +7 for Np, Pu) because 5f, 6d, and 7s orbitals are close in energy. All actinoids are radioactive, and only Th and U occur naturally in significant amounts.

The d- and f-Block Elements Important Equations for Class 12 Boards

Four equation sets have appeared repeatedly on CBSE and JEE Main. The list below states what each one proves and the years it surfaced, so revision time goes to the highest-yield set.

The d- and f-Block Elements Class 12: Glossary of Must-Know Terms

These nine terms appear in CBSE one-mark MCQs and assertion-reason questions almost every year. Lock in the one-line definition for each before attempting the PYQ set.

Frequently Asked d- and f-Block Questions in CBSE Board Exams (2021 to 2026)

The three patterns below recur almost every year in CBSE Class 12 Chemistry. Practise the reasoning behind each, not just the surface facts.

Ques. Why is the magnetic moment of Mn²⁺ higher than that of Fe³⁺ ? (CBSE 2023, 2025)

[2-Mark Question] Both Mn²⁺ and Fe³⁺ have the 3d⁵ configuration with five unpaired electrons, so the spin-only moments are identical at μ = √5 × 7 = 5.92 BM. CBSE awards full marks for showing the configurations and stating that both equal 5.92 BM.

Ques. Explain lanthanoid contraction and any two of its consequences. (CBSE 2021, 2024)

[3-Mark Question] Steady decrease in radii from La to Lu due to poor shielding by 4f electrons. Consequences: (i) similar sizes of Zr and Hf, Nb and Ta, making them chemically inseparable; (ii) decrease in basicity of trivalent hydroxides from La(OH)₃ to Lu(OH)₃.

Ques. Write balanced equations for the action of KMnO₄ on (i) Fe²⁺ and (ii) oxalic acid in acidic medium. (CBSE 2022, 2024)

[3-Mark Question] (i) MnO₄^- + 5Fe²⁺ + 8H⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O . (ii) 2MnO₄^- + 5C₂O₄^2- + 16H⁺ → 2Mn²⁺ + 10CO₂ + 8H₂O .

The d- and f-Block Elements Top 6 Formulae for Quick Recall

The six lines below are the formulae and reaction patterns you will use most often in CBSE and JEE Main numericals on this chapter. The complete master sheet with all redox half-reactions and oxidation-state ladders sits on the dedicated Collegedunia Formula Sheet for this chapter.

Full master table: The d- and f-Block Elements Class 12 Chemistry Formula Sheet

Class 12 Chemistry Chapter 4 Previous Year Questions Snapshot

A quick year-wise scan of where The d- and f-Block Elements surfaced across CBSE, JEE Main and NEET in the last six cycles. The fuller year-wise question map with topic tagging lives on the NCERT Solutions page for this chapter.

Full year-wise PYQ map: The d- and f-Block Elements Class 12 Chemistry NCERT Solutions

Common Misconceptions Students Hold in 12th Chemistry Chapter 4

These four wrong beliefs are responsible for most of the dropped marks on this chapter. Address them before the board paper and the chapter becomes a steady scorer.

• Calling Zn, Cd and Hg "transition elements". They have completely filled (n-1)d¹⁰ configurations in their ground state and in their common +2 oxidation state, so they fail the IUPAC definition. A consistent 1-mark loss in every cycle since 2022.
• Confusing lanthanoid contraction with actinoid contraction. Both happen, but actinoid contraction is more pronounced because 5f electrons shield less effectively than 4f. NEET 2023 tested this exact distinction.
• Writing the wrong configuration for Cr and Cu. Many students write 3d⁴ 4s² for Cr and 3d⁹ 4s² for Cu. The correct forms are 3d⁵ 4s¹ and 3d¹⁰ 4s¹ , driven by exchange-energy stabilisation of half-filled and fully filled d-orbitals.
• Forgetting H⁺ coefficients in KMnO₄ balancing. The five-electron change in acidic medium needs exactly 8 H⁺. Loss of even one coefficient costs a full mark in CBSE marking.

Class 12 Chemistry Chapter 4 Weightage Compared Across All Chapters

The visual below maps the typical CBSE marks distribution across all 10 chapters of the Class 12 Chemistry NCERT, averaged over the last five board papers. The d- and f-Block Elements sits in the middle band alongside Electrochemistry and Alcohols-Phenols-Ethers.

Related Links:

• The d- and f-Block Elements Class 12 Chemistry Handwritten Notes
• The d- and f-Block Elements Class 12 Chemistry Exemplar Solutions
• CBSE Class 12 Chemistry Sample Papers 2026

More d- and f-Block Elements Chemistry Class 12 Resources

NCERT Notes for Class 12 Chemistry: All Chapters

Cycle through any of the other nine chapters of the Class 12 Chemistry NCERT below. Each link opens the chapter's full revision notes page.