Transition Elements: General Characteristics

Introduction

Transition elements are the heart of inorganic chemistry - they’re everywhere from the hemoglobin in your blood (iron) to catalytic converters in cars (platinum). Understanding their unique properties is crucial for JEE success!

Definition of Transition Elements

IUPAC Definition

Transition elements are elements that have partially filled d-orbitals in their ground state OR in any of their commonly occurring oxidation states.

d-Block vs Transition Elements

Not all d-block elements are transition elements!

graph TD
    A[d-Block Elements] --> B[Transition Elements]
    A --> C[Non-Transition Elements]
    B --> B1[Sc, Ti, V, Cr, Mn, Fe, Co, Ni]
    C --> C1[Zn: 3d¹⁰4s²]
    C --> C2[Cu: 3d¹⁰4s¹, but Cu²⁺ has 3d⁹]

Exceptions:

• Zn, Cd, Hg: d¹⁰ configuration (fully filled d-orbitals) - NOT transition elements
• Cu, Ag, Au: Although ground state is d¹⁰s¹, their common oxidation states have partially filled d-orbitals - STILL transition elements

Position in Periodic Table

The Four Series

Note: Lanthanoids (58-71) and Actinoids (90-103) interrupt the 5d and 6d series respectively.

Electronic Configuration

General Configuration

First Transition Series (3d)

Interactive Demo: Visualize Transition Elements in Periodic Table

Explore the d-block elements, their positions, and electronic configurations.

Why d⁵ and d¹⁰ are Stable?

1. Exchange Energy: Maximum number of electron exchanges
2. Symmetrical Distribution: All d-orbitals equally occupied (d⁵) or fully occupied (d¹⁰)
3. Pairing Energy Minimization: Half-filled avoids pairing

Exchange stabilization:

• d⁵: 10 exchanges (↑ ↑ ↑ ↑ ↑)
• d¹⁰: 45 exchanges (↑↓ ↑↓ ↑↓ ↑↓ ↑↓)

General Characteristics

1. Metallic Character

All transition elements are metals with typical metallic properties:

• High density
• High melting and boiling points
• Metallic luster
• Good conductors of heat and electricity
• Malleable and ductile

Trends:

• Melting point generally increases across period (max at Cr/W)
• Exception: Mn and Tc have lower m.p. due to d⁵ configuration

2. Atomic and Ionic Radii

Across a Period:

• Generally decreases from left to right
• Decrease is small compared to s and p-block elements
• Reason: Poor shielding by d-electrons

Down a Group:

• Usually increases from 3d to 4d
• 4d and 5d series have similar radii (lanthanoid contraction effect)

graph LR
    A[3d series] -->|increase| B[4d series]
    B -->|similar| C[5d series]

    style B fill:#3498db
    style C fill:#3498db

3. Ionization Energy

Trends:

• Generally increases across the period (irregular)
• Higher than s-block, lower than p-block
• Small variation across series

Why irregular?

• d⁵ and d¹⁰ configurations have extra stability
• Cr (d⁵s¹) and Cu (d¹⁰s¹) have higher IE than expected

4. Oxidation States

Most characteristic property!

• Show variable oxidation states differing by 1
• Range: +2 to +7 (Mn shows all from +2 to +7)
• Common stable states: +2, +3

Rules:

1. Maximum oxidation state = Group number (up to Mn)
2. After Mn, maximum OS decreases (pairing energy consideration)
3. +2 state is common (loss of 2 electrons from ns orbital)
4. Higher oxidation states are more oxidizing

5. Magnetic Properties

Most transition metal compounds are paramagnetic due to unpaired electrons.

Magnetic moment (μ):

where n = number of unpaired electrons, BM = Bohr Magneton

Examples:

• Ti³⁺ (3d¹): n=1, μ = √3 = 1.73 BM
• Fe²⁺ (3d⁶): n=4, μ = √24 = 4.90 BM
• Cu²⁺ (3d⁹): n=1, μ = √3 = 1.73 BM
• Zn²⁺ (3d¹⁰): n=0, μ = 0 (diamagnetic)

6. Catalytic Properties

Transition metals and their compounds are excellent catalysts.

Reasons:

1. Variable oxidation states (can donate/accept electrons)
2. Form reaction intermediates
3. Provide large surface area (heterogeneous catalysis)

Examples:

• Fe: Haber process (N₂ + H₂ → NH₃)
• V₂O₅: Contact process (SO₂ → SO₃)
• Ni: Hydrogenation of oils
• Pt: Catalytic converters
• MnO₂: Decomposition of H₂O₂

7. Formation of Colored Compounds

Most transition metal compounds are colored due to d-d transitions.

Mechanism:

1. In presence of ligands, d-orbitals split into different energy levels
2. Electrons absorb visible light to jump between these levels
3. Complementary color is observed

Colorless exceptions (d⁰ or d¹⁰):

• Sc³⁺ (d⁰), Ti⁴⁺ (d⁰): Colorless
• Zn²⁺ (d¹⁰), Cu⁺ (d¹⁰): Colorless

8. Complex Formation

Transition metals readily form coordination complexes due to:

1. Small size and high charge
2. Availability of vacant d-orbitals
3. Ability to accept electron pairs from ligands

Examples:

• [Fe(CN)₆]⁴⁻, [Cu(NH₃)₄]²⁺, [Ni(CO)₄]

9. Alloy Formation

Transition metals form interstitial and substitutional alloys easily.

Reasons:

• Similar atomic radii
• Similar crystal structures
• Similar electronic configurations

Examples:

• Steel (Fe + C)
• Brass (Cu + Zn)
• Bronze (Cu + Sn)

10. Interstitial Compounds

Form compounds with small atoms (H, B, C, N) that occupy interstitial spaces in metal lattice.

Properties:

• Very hard
• High melting points
• Chemically inert
• Retain metallic conductivity

Examples:

• TiC, TiH₂, VH₀.₅₆

Comparison: 3d vs 4d vs 5d Series

Lanthanoid Contraction Effect: The 4d and 5d series have similar radii due to the lanthanoid contraction (poor shielding by 4f electrons).

Common JEE Mistakes

1. Assuming all d-block elements are transition elements

   • Wrong: Zn, Cd, Hg are NOT transition elements

2. Forgetting anomalous configurations

   • Cr: 3d⁵4s¹ (NOT 3d⁴4s²)
   • Cu: 3d¹⁰4s¹ (NOT 3d⁹4s²)

3. Maximum oxidation state confusion

   • Mn shows +7 (not Fe or Co)
   • After Mn, max OS decreases

4. Color and configuration

   • d⁰ and d¹⁰ compounds are colorless (no d-d transitions possible)

5. Magnetic moment calculation

   • Use spin-only formula: μ = √n(n+2)
   • Don’t forget to consider the actual configuration of the ion!

Practice Problems

Level 1: Basic Concepts

1. Why is Zn not considered a transition element?

2. Write the electronic configuration of:

   • Cr (Z=24)
   • Cu²⁺ (Z=29)
   • Fe³⁺ (Z=26)

3. Which transition metal shows the maximum number of oxidation states? Why?

Level 2: Application

4. Calculate the magnetic moment of:

   • Ti³⁺
   • V⁴⁺
   • Mn²⁺
   • Cu²⁺

5. Explain why:

   • Transition elements form colored compounds
   • Transition metals are good catalysts
   • Sc³⁺ is colorless but Ti³⁺ is colored

6. Compare the atomic radii:

   • Fe vs Co vs Ni
   • Zr vs Hf
   • Explain the trends

Level 3: JEE Advanced

7. The electronic configuration of Cr²⁺ ion is:

   • (a) [Ar]3d⁵4s¹
   • (b) [Ar]3d⁴
   • (c) [Ar]3d⁴4s²
   • (d) [Ar]3d²4s²

8. Which of the following pairs of compounds show different colors?

   • (a) TiO₂ and VO₂
   • (b) CuSO₄ and ZnSO₄
   • (c) FeSO₄ and FeCl₂
   • (d) MnO and MnO₂

9. A transition metal ion has magnetic moment of 3.87 BM. If it belongs to 3d series, identify the possible ions.

10. Assertion (A): Transition elements form a large number of complexes. Reason (R): Transition elements have small size and high nuclear charge.

    • (a) Both A and R are true, R explains A
    • (b) Both A and R are true, R doesn’t explain A
    • (c) A is true, R is false
    • (d) Both are false

Memory Tricks

“CCFM VCM” Mnemonic

Characteristics of Transition Elements:

• Catalytic activity
• Complex formation
• Form alloys
• Magnetic properties
• Variable oxidation states
• Colored compounds
• Metallic properties

“Chromium & Copper - Half & Full!”

For anomalous configurations:

• Chromium → Half-filled d⁵
• Copper → Full-filled d¹⁰

“Zinc Never Transitions!”

To remember Zn is NOT a transition element:

• Zinc
• Never
• Transitions (Because it has fully filled d-orbitals)

Related Topics

Within d-f Block Elements

• Properties of d-Block Elements - Color, magnetism, oxidation states
• Important Compounds - K₂Cr₂O₇, KMnO₄ chemistry
• Lanthanoids - 4f series properties
• Actinoids - 5f series and radioactivity

Cross-Subject: Physics Connections

• Electromagnetic Radiation - Color origin in compounds
• Magnetism - Paramagnetism and diamagnetism

Other Chemistry Topics

• Coordination Compounds - Complex formation
• Chemical Bonding - Hybridization in complexes
• Periodic Classification - Trends across periods

Properties of d-Block Elements →