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The d- and f-Block Elements
The d- and f-block elements are studied through their position, electronic configuration, oxidation states, colours, magnetic behaviour, catalytic properties, and compound formation. The chapter connects periodic trends with observable properties such as coloured ions, variable valency, and paramagnetism. Transition elements are especially important because their partially filled d-orbitals allow variable oxidation states, complex formation, alloy formation, and catalytic activity. These properties are frequently tested through reasons, comparisons, trend-based questions, and application examples. The compounds potassium permanganate and potassium dichromate are important oxidising agents. Their preparation, colour changes, oxidation-state changes, and acidic-medium reactions are useful for reaction-based and observation-based CBSE questions. The f-block section focuses on lanthanoids and actinoids, especially lanthanoid contraction, common oxidation states, actinoid variability, and uses such as misch metal. You should connect contraction and shielding with similarities in later elements and separation difficulties.
Difficulty
Medium
Study time
70-90 min
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Last-pass revision
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Targeted practice
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First full pass
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Key Concepts
Work through the concepts in order. Each one has an explanation, a worked example, a self-check and an exam answer.
All Concepts
All 6 concepts of the chapter, in the order the NCERT chapter teaches them.
Position of d-Block Elements in the Periodic Table
d-block elements are elements in which the differentiating electron enters the d-subshell of the penultimate shell. They are placed between the s-block and p-block elements in the periodic table.
General Properties of Transition Metals
Transition metals show characteristic properties such as variable oxidation states, coloured ions, paramagnetism, complex formation, catalytic activity, high enthalpy of atomisation, high melting points, and alloy formation due to involvement of d-electrons.
Trends in Atomic and Ionic Radii
Across a transition series, atomic and ionic radii generally decrease at first due to increasing nuclear charge, but the decrease becomes small because added d-electrons shield each other poorly. In f-block elements, poor shielding by f-electrons causes lanthanoid contraction.
Magnetic Properties and the Spin-Only Formula
Magnetic behaviour of transition-metal ions depends mainly on the number of unpaired electrons. Paramagnetic species have unpaired electrons, while diamagnetic species have all electrons paired.
Preparation and Oxidising Properties of KMnO4 and K2Cr2O7
Potassium permanganate and potassium dichromate are important transition-metal compounds used as strong oxidising agents, especially in acidic medium. Their reactions involve reduction of Mn(VII) or Cr(VI) to lower oxidation states.
Lanthanoids and Actinoids
Lanthanoids and actinoids are f-block elements in which differentiating electrons enter 4f and 5f orbitals respectively. Lanthanoids commonly show +3 oxidation state, while actinoids show greater oxidation-state variability.
Exam Intelligence
The traps that cost marks in this chapter, and how its main concepts turn up in the paper.
Common Traps
- Calling every d-block element a typical transition element without checking incomplete d-orbitals.
- Counting neutral-atom electrons instead of ion electrons for magnetic moment questions.
- Using oxidation state as n in the spin-only formula instead of number of unpaired electrons.
- Ignoring the reaction medium for KMnO4 and writing the wrong manganese product.
- Saying lanthanoids show only +3 without remembering important +2 and +4 exceptions.
How CBSE Asks This Chapter
- Position of d-Block Elements in the Periodic Table
Questions usually ask students to define transition elements, locate the 3d series, or explain why Zn, Cd, and Hg are not typical transition elements.
- General Properties of Transition Metals
CBSE questions often ask for reasons for colour, magnetic nature, variable oxidation states, alloy formation, or catalytic behaviour, usually with a named ion or metal.
- Trends in Atomic and Ionic Radii
It is commonly asked as a reason for lanthanoid contraction, similarity of Zr and Hf, separation difficulty of lanthanoids, or small change in radii across transition series.
- Magnetic Properties and the Spin-Only Formula
Questions may ask for magnetic moment, number of unpaired electrons, comparison of magnetic strength, or identification of para- and diamagnetic ions.
Quick Revision
Concept, formula or equation to remember, and the trap that loses marks — in one scannable view.
Position of d-Block Elements in the Periodic Table
Remember
d-block elements have differentiating electrons entering (n-1)d orbitals.Trap to avoid
Students often call every d-block element a transition element without checking whether the atom or its common ion has a partially filled d-subshell.
General Properties of Transition Metals
Remember
Property-cause pattern: variable oxidation state arises from comparable ns and (n-1)d energies; paramagnetism depends on unpaired electrons; colour generally requires partially filled d-orbitals; complex formation is favoured by small size, charge, and available orbitals.Trap to avoid
Students often give one reason for all properties.
Trends in Atomic and Ionic Radii
Remember
Trend rule: across a transition series, effective nuclear charge generally increases because d-electrons shield poorly.Trap to avoid
Students often say size always decreases uniformly across the d-block.
Magnetic Properties and the Spin-Only Formula
Remember
Spin-only formula: magnetic moment = √(n(n+2)) BM, where n is the number of unpaired electrons and BM means Bohr magneton.Trap to avoid
Students often count electrons in the neutral atom instead of the ion.
Preparation and Oxidising Properties of KMnO4 and K2Cr2O7
Remember
Key acidic-medium reductions: MnO4- + 8H+ + 5e− → Mn2+ + 4H2O; Cr2O7 2- + 14H+ + 6e− → 2Cr3+ + 7H2O.Trap to avoid
Students often ignore the medium.
Remember
Trend rule: lanthanoids mainly show +3 oxidation state and exhibit lanthanoid contraction due to poor 4f shielding.Trap to avoid
Students often assume lanthanoids and actinoids behave identically because both are f-block series.
| Concept | Remember | Trap to avoid |
|---|---|---|
| Position of d-Block Elements in the Periodic Table | d-block elements have differentiating electrons entering (n-1)d orbitals. | Students often call every d-block element a transition element without checking whether the atom or its common ion has a partially filled d-subshell. |
| General Properties of Transition Metals | Property-cause pattern: variable oxidation state arises from comparable ns and (n-1)d energies; paramagnetism depends on unpaired electrons; colour generally requires partially filled d-orbitals; complex formation is favoured by small size, charge, and available orbitals. | Students often give one reason for all properties. |
| Trends in Atomic and Ionic Radii | Trend rule: across a transition series, effective nuclear charge generally increases because d-electrons shield poorly. | Students often say size always decreases uniformly across the d-block. |
| Magnetic Properties and the Spin-Only Formula | Spin-only formula: magnetic moment = √(n(n+2)) BM, where n is the number of unpaired electrons and BM means Bohr magneton. | Students often count electrons in the neutral atom instead of the ion. |
| Preparation and Oxidising Properties of KMnO4 and K2Cr2O7 | Key acidic-medium reductions: MnO4- + 8H+ + 5e− → Mn2+ + 4H2O; Cr2O7 2- + 14H+ + 6e− → 2Cr3+ + 7H2O. | Students often ignore the medium. |
| Lanthanoids and Actinoids | Trend rule: lanthanoids mainly show +3 oxidation state and exhibit lanthanoid contraction due to poor 4f shielding. | Students often assume lanthanoids and actinoids behave identically because both are f-block series. |
Practice
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