d- and f-Block Elements

Master transition metals, lanthanoids, actinoids, and their compounds for JEE Chemistry.

d-Block elements (transition metals) and f-block elements (inner transition metals) have unique properties due to partially filled d or f orbitals.

Overview

graph TD
    A[d- and f-Block] --> B[Transition Elements]
    A --> C[Lanthanoids]
    A --> D[Actinoids]
    B --> B1[Variable Oxidation]
    B --> B2[Colored Compounds]
    B --> B3[Complex Formation]

d-Block Elements

General Characteristics

  • Configuration: (n-1)d¹⁻¹⁰ ns⁰⁻²
  • Variable oxidation states
  • Form colored compounds
  • Good catalysts
  • Paramagnetic (usually)
  • Form complexes

Electronic Configuration

First Row (3d series):

ElementConfigAnomaly
Cr[Ar]3d⁵4s¹Half-filled d
Cu[Ar]3d¹⁰4s¹Fully-filled d

Oxidation States

  • Most stable: +2, +3
  • Maximum: equals group number (up to Mn)
  • Higher states are oxidizing

Colored Compounds

Due to d-d transitions. Color depends on:

  • Number of d electrons
  • Ligand field strength
  • Geometry
JEE Tip
Compounds with d⁰ or d¹⁰ configuration are usually colorless (no d-d transition possible).

Important Compounds

Potassium Dichromate (K₂Cr₂O₇)

  • Orange color
  • Strong oxidizing agent
  • In acidic medium: Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O

Potassium Permanganate (KMnO₄)

  • Purple color
  • Strong oxidizing agent
  • In acidic medium: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O
  • In basic medium: MnO₄⁻ + 2H₂O + 3e⁻ → MnO₂ + 4OH⁻

f-Block Elements

Lanthanoids (4f series)

Elements: Ce to Lu (58-71)

Characteristics:

  • Most common oxidation state: +3
  • Show lanthanoid contraction
  • Similar chemical properties
  • Colored ions (f-f transitions)

Lanthanoid Contraction

Gradual decrease in atomic/ionic radii from La to Lu.

Cause: Poor shielding by 4f electrons

Consequences:

  • Similar radii of 4d and 5d elements
  • Separation of lanthanoids is difficult
  • Similar properties across the series

Actinoids (5f series)

Elements: Th to Lr (90-103)

Characteristics:

  • Variable oxidation states (+3 to +7)
  • Radioactive
  • Form more complex ions than lanthanoids

Practice Problems

  1. Why do transition metals show variable oxidation states?

  2. Explain why Cu²⁺ compounds are colored but Cu⁺ compounds are colorless.

  3. What is lanthanoid contraction? Give its consequences.

Quick Check
Why is KMnO₄ purple while K₂MnO₄ is green?

Further Reading