Unit 4:- d and f block elements chemistry class 12

Unit 4: d- and f-Block Elements

Unit 4: d- and f-Block Elements

Part A: d-Block Elements (Transition Metals)

1. General Introduction

The d-block elements are found in groups 3 to 12 of the periodic table. These elements have partially filled d-orbitals either in ground state or in one of their oxidation states.

2. Electronic Configuration

The general configuration of d-block elements is:

[Noble Gas] (n-1)d1-10 ns0-2
  • First row (3d series): Sc (Z=21) to Zn (Z=30)
  • Second row (4d series): Y (Z=39) to Cd (Z=48)
  • Third row (5d series): La (Z=57), Hf (Z=72) to Hg (Z=80)

3. Occurrence and Characteristics

  • Mostly found in ores like oxides, sulphides, and halides.
  • Good conductors of heat and electricity.
  • Exhibit variable oxidation states.
  • High melting and boiling points.

4. General Trends in Properties (First Row)

(a) Metallic Character

All are metals, show malleability, ductility, conductivity, and luster.

(b) Ionization Enthalpy

Relatively high due to nuclear attraction, but lower than s- and p-block elements.

(c) Oxidation States

These elements show variable oxidation states due to participation of (n-1)d and ns electrons.
  • Fe: +2, +3
  • Mn: +2 to +7

(d) Ionic Radii

Decrease across the period due to increased nuclear charge → stronger pull on electrons.

(e) Colour

Many transition metal ions are coloured due to d-d electron transitions.

(f) Catalytic Properties

  • Transition metals and their compounds act as good catalysts (e.g., Fe in Haber process).

(g) Magnetic Properties

Paramagnetic due to unpaired d electrons. Magnetic moment:

μ = √[n(n+2)] BM

where n = number of unpaired electrons.

(h) Interstitial Compounds

  • Small atoms like H, B, C, N occupy voids in metal lattice (e.g., TiC, Fe3H).

(i) Alloy Formation

Transition metals form strong and hard alloys (e.g., brass = Cu + Zn).

5. Important Compounds

Potassium Dichromate (K2Cr2O7)

  • Preparation: From chromite ore.
  • Properties: Orange crystals, strong oxidising agent in acidic medium.

Potassium Permanganate (KMnO4)

  • Preparation: From pyrolusite (MnO2).
  • Properties: Deep purple, strong oxidising agent in acidic, neutral, and basic media.

Part B: f-Block Elements

1. Lanthanides (4f Series)

Electronic Configuration

General: [Xe] 4f1–14 5d0–1 6s2

Oxidation States

+3 is most common; some show +2 or +4 (e.g., Ce+4, Eu+2).

Chemical Reactivity

  • Reactive, especially with water and acids.
  • Form ionic, basic oxides.

Lanthanide Contraction

Gradual decrease in size of atoms and ions across the lanthanide series due to poor shielding by 4f electrons.

Consequences of Lanthanide Contraction

  • Similarity in properties of second and third-row transition elements (Zr ~ Hf).
  • Separation of lanthanides becomes difficult.

2. Actinides (5f Series)

Electronic Configuration

General: [Rn] 5f1–14 6d0–1 7s2

Oxidation States

More variable than lanthanides, ranging from +3 to +6 (e.g., U+6).

Comparison with Lanthanides

  • Actinides are more reactive.
  • Show greater oxidation state variability.
  • Radioactive in nature.

Tips for Teaching Effectively:

  • Use periodic table handouts to visualize positions of d and f block.
  • Compare properties across rows to reinforce trends.
  • Demonstrate oxidation reactions of KMnO₄ and K₂Cr₂O₇ with common reducing agents.
  • Explain magnetic properties using diagrams of d-orbital filling.
  • Use mnemonic devices to help remember lanthanide series (e.g., "La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu").

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