Quick Summary
d-Block elements (transition metals) and f-Block elements (lanthanides and actinides) are central to inorganic chemistry. This chapter carries 8–10 marks in TN HSE. Focus on trends in d-block, colour and magnetic properties, and the concept of lanthanoid contraction.
d-Block (Transition Metals) — General Properties
Definition: Elements with incompletely filled d-orbitals in ground state or in any common oxidation state.
| Property | Reason |
|---|---|
| Variable oxidation states | Both (n-1)d and ns electrons available |
| Coloured compounds | d–d electron transitions |
| Paramagnetic behaviour | Unpaired d-electrons |
| Catalytic activity | Variable valency, ability to adsorb reactants |
| Complex formation | Small size, high charge, available d-orbitals |
Trends Across 3d Series (Sc to Zn)
- Atomic radius: Decreases slightly then increases at the end (Zn largest)
- Ionisation enthalpy: Increases across the period (irregular due to d-electron repulsions)
- Density: Generally increases (Cr is exception — low due to bcc structure)
- Melting point: Peaks at Cr (strongest metallic bonding); Zn lowest (d¹⁰, no unpaired)
- Colour of ions:
| Ion | Config | Colour |
|---|---|---|
| Sc³⁺ | d⁰ | Colourless |
| Ti³⁺ | d¹ | Purple |
| Cr³⁺ | d³ | Violet |
| Mn²⁺ | d⁵ | Pale pink |
| Fe³⁺ | d⁵ | Yellow |
| Cu²⁺ | d⁹ | Blue |
| Zn²⁺ | d¹⁰ | Colourless |
Magnetic Properties
Paramagnetic: Contains unpaired electrons; attracted by magnetic field. Diamagnetic: All electrons paired; repelled by magnetic field.
Magnetic moment (μ): μ = √n(n+2) BM, where n = number of unpaired electrons
| Ion | Unpaired e⁻ | μ (BM) |
|---|---|---|
| Mn²⁺ | 5 | 5.92 |
| Fe³⁺ | 5 | 5.92 |
| Fe²⁺ | 4 | 4.90 |
| Cu²⁺ | 1 | 1.73 |
Important Catalysts from d-Block
- Fe: Haber's process (N₂ + H₂ → NH₃)
- V₂O₅: Contact process (SO₂ → SO₃)
- Pt/Rh: Ostwald's process
- Ni: Hydrogenation of oils
- MnO₂: Decomposition of KClO₃
f-Block Elements
Lanthanides (Lanthanoids) — 4f Series
1. Zr and Hf have nearly identical radii (used as twins) 2. 4d and 5d elements of same group have similar properties 3. Separation of lanthanoids is difficult
- Elements: La (57) to Lu (71)
- General configuration: [Xe] 4f¹⁻¹⁴ 5d⁰⁻¹ 6s²
- Common oxidation state: +3
- Lanthanoid contraction: Steady decrease in size La→Lu due to poor 4f shielding
- Consequences of lanthanoid contraction:
Actinides (Actinoids) — 5f Series
- Elements: Ac (89) to Lr (103)
- More variable oxidation states than lanthanides
- Highly radioactive; mostly synthetic
- Uranium (U) and Thorium (Th) are important: used in nuclear fuel
Lanthanides vs Actinides
| Property | Lanthanides | Actinides |
|---|---|---|
| Orbital filled | 4f | 5f |
| Radioactivity | Non-radioactive | All radioactive |
| Oxidation states | Mainly +3 | +3 to +7 |
| Magnetic properties | Less complex | More complex |
Important Questions
One Mark
1. Define transition metals. 2. What is lanthanoid contraction? 3. Why is Zn not considered a transition metal? 4. Give the formula for magnetic moment. 5. Name a catalyst derived from a transition metal.
Short Answer (3 marks)
1. Explain why transition metals form coloured compounds. 2. What is lanthanoid contraction? State two consequences. 3. Why do transition metals show variable oxidation states?
Long Answer (5 marks)
1. Discuss the general properties of transition metals with reference to ionisation energy, colour, magnetic properties, and catalytic activity. 2. Compare lanthanides and actinides in terms of electronic configuration, oxidation states, and magnetic properties.
Board Exam Tips
- Magnetic moment calculation μ = √n(n+2) — always check the number of unpaired electrons first
- Zn, Cd, Hg are NOT true transition metals (d¹⁰ in ground state AND all stable states)
- Lanthanoid contraction — remember the word "poor shielding of 4f electrons"
- Consequences of lanthanoid contraction: Zr/Hf similarity is a classic exam point
Revision Checklist
- [ ] General trends in d-block
- [ ] Colour of common transition metal ions
- [ ] Magnetic moment formula and calculation
- [ ] Lanthanoid contraction and its consequences
- [ ] Differences: lanthanides vs actinides
- [ ] Important transition metal catalysts
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