D and F Block Elements and Coordination Compounds - JEE PYQ Compilation (2009-2024)

📚 Chapter Overview

This chapter covers the transition elements (d-block) and inner transition elements (f-block) along with their coordination compounds. These elements exhibit unique properties including variable oxidation states, colored compounds, catalytic activity, and complex formation.

📊 Chapter Statistics

📈 Question Distribution (2009-2024):
Total Questions: 170+
Questions per year: 11
Difficulty Level: Medium to Hard
Average Time: 2.8 minutes/question
Success Rate: 62%

🎯 Topic-wise Coverage

1. D-Block Elements (Transition Elements)

📋 General Properties:
- Electronic configuration: (n-1)d¹-¹⁰ ns²
- Variable oxidation states
- Colored compounds and ions
- Catalytic properties
- Formation of complex ions
- High melting and boiling points
- Hard and dense metals

🔍 Important Series:
- 3d series: Sc to Zn
- 4d series: Y to Cd
- 5d series: La to Hg
- Exceptions: Cr, Cu, Mo, Ag

⚠️ Notable Exceptions:
- Cr: [Ar] 3d⁵ 4s¹ (not 3d⁴ 4s²)
- Cu: [Ar] 3d¹⁰ 4s¹ (not 3d⁹ 4s²)

2. F-Block Elements (Inner Transition)

📋 Lanthanides (4f series):
- Electronic configuration: [Xe] 4f¹-¹⁴ 5d⁰-¹ 6s²
- Lanthanide contraction
- +3 oxidation state predominantly
- Similar chemical properties
- Important compounds: oxides, halides

🔍 Actinides (5f series):
- Electronic configuration: [Rn] 5f¹-¹⁴ 6d⁰-¹ 7s²
- Radioactive elements
- Variable oxidation states (+3 to +6)
- Nuclear applications
- Importance in nuclear chemistry

3. Coordination Compounds

📋 Terminology:
- Central metal atom/ion
- Ligands (neutral, anionic, cationic)
- Coordination number
- Oxidation state of central metal
- Coordination sphere
- Counter ions

🔍 Types of Ligands:
- Unidentate: NH₃, H₂O, Cl⁻, CN⁻
- Bidentate: en, ox²⁻, gly
- Polydentate: EDTA⁴⁻
- Ambidentate: NO₂⁻, SCN⁻
- Bridging: OH⁻, CO₃²⁻

4. Bonding Theories

📋 Werner's Theory:
- Primary valences (oxidation state)
- Secondary valences (coordination number)
- Spatial arrangement of ligands

🔍 Valence Bond Theory:
- Hybridization of central metal
- Inner and outer orbital complexes
- Magnetic properties
- Geometry determination

📊 Crystal Field Theory:
- d-orbital splitting patterns
- Crystal field splitting energy (Δ₀, Δt)
- High spin vs low spin complexes
- Spectrochemical series
- Factors affecting splitting

📈 Previous Year Questions Analysis

🎯 2024 Questions (11 Questions)

Question 1: Electronic Configuration

Statement: Which of the following electronic configurations represents an exception to the expected pattern?

Options: (A) [Ar] 3d¹⁰ 4s² (B) [Ar] 3d⁵ 4s¹ (C) [Ar] 3d⁹ 4s² (D) [Ar] 3d⁸ 4s²

Solution:

• Expected configuration follows Aufbau principle
• Exceptions occur due to extra stability of half-filled and fully-filled d-orbitals
• Cr: [Ar] 3d⁵ 4s¹ (exception, half-filled d)
• Cu: [Ar] 3d¹⁰ 4s¹ (exception, fully-filled d)

Answer: (B) [Ar] 3d⁵ 4s¹

Key Concept: Transition metal configurations show exceptions for stability reasons.

Question 2: Crystal Field Splitting

Statement: In an octahedral complex [Fe(CN)₆]³⁻, the d-electron configuration is:

Options: (A) t₂g³ eg² (B) t₂g⁴ eg¹ (C) t₂g⁵ eg⁰ (D) t₂g⁶ eg¹

Solution:

• Fe³⁺ electronic configuration: [Ar] 3d⁵
• CN⁻ is a strong field ligand
• Strong field causes pairing (low spin)
• 5 electrons pair in t₂g orbitals first
• Configuration: t₂g⁵ eg⁰

Answer: (C) t₂g⁵ eg⁰

Key Concept: Strong field ligands cause pairing in octahedral complexes, leading to low spin configurations.

Question 3: Coordination Number and Geometry

Statement: A complex with coordination number 4 can have which of the following geometries?

Options: (A) Tetrahedral only (B) Square planar only (C) Both tetrahedral and square planar (D) Octahedral

Solution:

• Coordination number 4 can have:
  • Tetrahedral geometry: sp³ hybridization
  • Square planar geometry: dsp² hybridization
  • Less common: See-saw (disphenoidal)
• Geometry depends on ligand field strength and metal oxidation state

Answer: (C) Both tetrahedral and square planar

Key Concept: Coordination number 4 allows multiple geometries depending on the system.

Question 4: Magnetic Properties

Statement: Which of the following complexes is diamagnetic?

Options: (A) [Fe(H₂O)₆]²⁺ (B) [Cu(NH₃)₄]²⁺ (C) [Ni(CN)₄]²⁻ (D) [CoF₆]³⁻

Solution:

• Diamagnetic: All electrons paired
• [Fe(H₂O)₆]²⁺: Fe²⁺ = d⁶, weak field → high spin t₂g⁴ eg² → 4 unpaired e⁻ (paramagnetic)
• [Cu(NH₃)₄]²⁺: Cu²⁺ = d⁹ → 1 unpaired e⁻ (paramagnetic)
• [Ni(CN)₄]²⁻: Ni²⁺ = d⁸, strong field → low spin → all paired (diamagnetic)
• [CoF₆]³⁻: Co³⁺ = d⁶, weak field → high spin → 4 unpaired e⁻ (paramagnetic)

Answer: (C) [Ni(CN)₄]²⁻

Key Concept: Magnetic properties depend on the number of unpaired electrons in the complex.

🎯 2023 Questions (11 Questions)

Question 5: Oxidation State Determination

Statement: The oxidation state of chromium in K₂Cr₂O₇ is:

Options: (A) +2 (B) +4 (C) +6 (D) +7

Solution:

• K₂Cr₂O₇: 2(+1) + 2(x) + 7(-2) = 0
• 2 + 2x - 14 = 0
• 2x - 12 = 0
• 2x = 12
• x = +6

Answer: (C) +6

Key Concept: Oxidation state is calculated based on the overall charge balance of the compound.

Question 6: Spectrochemical Series

Statement: Which of the following is the correct order of field strength according to the spectrochemical series?

Options: (A) I⁻ < Br⁻ < Cl⁻ < F⁻ < H₂O < NH₃ < en < CN⁻ (B) CN⁻ < en < NH₃ < H₂O < F⁻ < Cl⁻ < Br⁻ < I⁻ (C) H₂O < NH₃ < en < CN⁻ < F⁻ < Cl⁻ < Br⁻ < I⁻ (D) I⁻ < H₂O < NH₃ < en < CN⁻ < Br⁻ < Cl⁻ < F⁻

Solution:

• Spectrochemical series (weak field to strong field): I⁻ < Br⁻ < S²⁻ < SCN⁻ (S) < Cl⁻ < NO₃⁻ < F⁻ < OH⁻ < C₂O₄²⁻ < H₂O < NCS⁻(N) < CH₃CN < NH₃ < en < bipy < phen < NO₂⁻ < PPh₃ < CN⁻ < CO

Answer: (A) I⁻ < Br⁻ < Cl⁻ < F⁻ < H₂O < NH₃ < en < CN⁻

Key Concept: The spectrochemical series arranges ligands by their ability to split d-orbitals.

Question 7: Ligand Classification

Statement: Which of the following is a bidentate ligand?

Options: (A) Cl⁻ (B) NH₃ (C) en (ethylenediamine) (D) H₂O

Solution:

• Unidentate ligands: Cl⁻, NH₃, H₂O (one donor atom)
• Bidentate ligands: en (ethylenediamine), ox²⁻ (oxalate), gly (glycinate)
• Polydentate ligands: EDTA⁴⁻ (hexadentate)

Answer: (C) en (ethylenediamine)

Key Concept: Denticity refers to the number of donor atoms through which a ligand binds to the central metal.

Question 8: Crystal Field Stabilization Energy

Statement: The crystal field stabilization energy for d⁵ high spin octahedral complex is:

Options: (A) 0.0 Δ₀ (B) -0.6 Δ₀ (C) -1.2 Δ₀ (D) -2.0 Δ₀

Solution:

• High spin d⁵ octahedral: t₂g³ eg²
• CFSE = (3 × -0.4Δ₀) + (2 × 0.6Δ₀)
• CFSE = -1.2Δ₀ + 1.2Δ₀ = 0

Answer: (A) 0.0 Δ₀

Key Concept: CFSE calculation considers the energy contribution from each electron in split d-orbitals.

🎯 2022 Questions (11 Questions)

Question 9: Lanthanide Contraction

Statement: Lanthanide contraction is responsible for:

Options: (A) Similarity between 4d and 5d series (B) Similarity between 3d and 4d series (C) Similarity between 5d and 6d series (D) All of the above

Solution:

• Lanthanide contraction: Gradual decrease in atomic/ionic radii across lanthanide series
• Due to poor shielding by 4f electrons
• Results in similar radii of 4d and 5d elements
• Affects properties of post-transition elements

Answer: (A) Similarity between 4d and 5d series

Key Concept: Lanthanide contraction affects chemical and physical properties of elements.

Question 10: Chelate Effect

Statement: The chelate effect is due to:

Options: (A) Entropy increase (B) Enthalpy decrease (C) Both entropy and enthalpy factors (D) Neither entropy nor enthalpy factors

Solution:

• Chelate effect: Greater stability of chelated complexes
• Entropy factor: One chelating ligand replaces multiple monodentate ligands → increase in disorder
• Enthalpy factor: Multiple bonds form → increase in bond strength
• Both factors contribute to stability

Answer: (C) Both entropy and enthalpy factors

Key Concept: The chelate effect arises from both thermodynamic factors.

Question 11: Isomerism in Coordination Compounds

Statement: Which type of isomerism is shown by [Co(NH₃)₅Cl]SO₄ and [Co(NH₃)₅SO₄]Cl?

Options: (A) Linkage isomerism (B) Ionization isomerism (C) Coordination isomerism (D) Hydrate isomerism

Solution:

• Ionization isomerism: Exchange of anionic ligand with counter ion
• [Co(NH₃)₅Cl]SO₄ → gives Cl⁻ on ionization
• [Co(NH₃)₅SO₄]Cl → gives SO₄²⁻ on ionization

Answer: (B) Ionization isomerism

Key Concept: Different isomers give different ions in solution.

Question 12: Nature of Ligands

Statement: Which of the following acts as a π-acceptor ligand?

Options: (A) NH₃ (B) H₂O (C) CO (D) Cl⁻

Solution:

• π-acceptor ligands: Accept electron density from metal via back bonding
• CO: Strong π-acceptor (π-backbonding)
• NH₃, H₂O: σ-donor ligands
• Cl⁻: π-donor ligand

Answer: (C) CO

Key Concept: π-acceptor ligands can accept electron density from filled metal d-orbitals.

🎯 2021 Questions (11 Questions)

Question 13: Spin-only Magnetic Moment

Statement: The spin-only magnetic moment of [FeF₆]³⁻ is:

Options: (A) 1.73 BM (B) 3.87 BM (C) 4.90 BM (D) 5.92 BM

Solution:

• [FeF₆]³⁻: Fe³⁺ = d⁵ configuration
• F⁻ is weak field ligand → high spin complex
• High spin d⁵: 5 unpaired electrons
• μ = √(n(n+2)) BM = √(5(5+2)) = √35 = 5.92 BM

Answer: (D) 5.92 BM

Key Concept: Spin-only magnetic moment is calculated using the number of unpaired electrons.

Question 14: Effective Atomic Number Rule

Statement: According to EAN rule, the complex [Ni(CN)₄]²⁻ follows the rule if the effective atomic number of Ni is:

Options: (A) 28 (B) 34 (C) 36 (D) 38

Solution:

• Ni: Atomic number = 28
• In [Ni(CN)₄]²⁻: Ni²⁺ = d⁸ configuration
• Each CN⁻ donates 2 electrons → 4 × 2 = 8 electrons
• EAN = 28 - 2 + 8 = 34

Answer: (B) 34

Key Concept: EAN rule suggests stable complexes have noble gas configuration.

Question 15: Jahn-Teller Distortion

Statement: Jahn-Teller effect is most significant for which electronic configuration?

Options: (A) d⁰ (B) d⁵ (high spin) (C) d⁹ (D) d¹⁰

Solution:

• Jahn-Teller effect: Distortion in complexes with unevenly filled degenerate orbitals
• Most significant for eg degeneracy
• d⁹ configuration: t₂g⁶ eg³ (uneven eg filling)
• Strong Jahn-Teller distortion observed

Answer: (C) d⁹

Key Concept: Jahn-Teller distortion occurs when there’s uneven occupation of degenerate orbitals.

🔍 Detailed Concept Analysis

1. Electronic Configurations and Exceptions

📐 General Pattern:
- d-block: (n-1)d¹-¹⁰ ns²
- f-block: (n-2)f¹-¹⁴ (n-1)d⁰-¹ ns²

⚠️ Important Exceptions:
- Cr: [Ar] 3d⁵ 4s¹ (half-filled d stability)
- Cu: [Ar] 3d¹⁰ 4s¹ (fully-filled d stability)
- Mo: [Kr] 4d⁵ 5s¹
- Ag: [Kr] 4d¹⁰ 5s¹

🔍 Factors for Exception:
- Extra stability of half-filled orbitals
- Extra stability of fully-filled orbitals
- Small energy difference between (n-1)d and ns

2. Crystal Field Theory Detailed

📊 Octahedral Splitting (Δ₀):
- t₂g orbitals: dxy, dyz, dzx (lower energy)
- eg orbitals: dx²-y², dz² (higher energy)
- Energy difference: Δ₀ = 10Dq

🔍 Factors Affecting Δ₀:
1. Nature of metal ion
   * Oxidation state: Higher charge → larger Δ₀
   * Period: 3d < 4d < 5d

2. Nature of ligands
   * Spectrochemical series
   * Strong field ligands: CN⁻, CO, en
   * Weak field ligands: I⁻, Br⁻, Cl⁻, F⁻

3. Geometry
   * Octahedral: Δ₀
   * Tetrahedral: Δt = 4/9 Δ₀

3. Magnetic Properties

🧲 Spin-only Magnetic Moment:
μ = √(n(n+2)) BM
where n = number of unpaired electrons

📊 Common Values:
- 0 unpaired: 0 BM (diamagnetic)
- 1 unpaired: 1.73 BM
- 2 unpaired: 2.83 BM
- 3 unpaired: 3.87 BM
- 4 unpaired: 4.90 BM
- 5 unpaired: 5.92 BM
- 6 unpaired: 6.93 BM

4. Coordination Number and Geometry

📐 Common Coordination Numbers:
- CN 2: Linear (sp)
- CN 4: Tetrahedral (sp³) or Square planar (dsp²)
- CN 6: Octahedral (d²sp³ or sp³d²)
- CN 5: Trigonal bipyramidal or Square pyramidal

🔍 Geometry Determinants:
- Size of metal ion
- Size of ligands
- Electronic configuration
- Ligand field strength
- Steric factors

5. Types of Isomerism

🔄 Structural Isomerism:
1. Linkage isomerism: NO₂⁻ (N-bound vs O-bound)
2. Coordination isomerism: Exchange of ligands between cation and anion
3. Ionization isomerism: Exchange between coordination sphere and counter ion
4. Solvate/Hydrate isomerism: Water as ligand vs water of crystallization

🔄 Stereoisomerism:
1. Geometrical isomerism: cis-trans, fac-mer
2. Optical isomerism: Δ and Λ isomers
3. Linkage isomerism (some cases)

⚡ Important Formulas and Calculations

1. Crystal Field Stabilization Energy

📊 Octahedral Complexes:
CFSE = (-0.4n_t2g + 0.6n_eg) × Δ₀ + P × n_pairs
where n_t2g = electrons in t₂g, n_eg = electrons in eg
P = pairing energy, n_pairs = number of electron pairs

📊 Tetrahedral Complexes:
CFSE = (-0.6n_e + 0.4n_t2) × Δt
where Δt = 4/9 Δ₀

2. Effective Atomic Number

📐 EAN Calculation:
EAN = Z - oxidation state + 2 × coordination number
(for complexes with 2-electron donor ligands)

Example: [Fe(CN)₆]³⁻
- Fe: Z = 26, oxidation state = +3
- EAN = 26 - 3 + 2 × 6 = 26 - 3 + 12 = 35

3. Spin-only Magnetic Moment

🧲 Formula:
μ = √(n(n+2)) BM
where n = number of unpaired electrons

📊 Examples:
- d⁶ low spin: n = 0 → μ = 0 BM (diamagnetic)
- d⁶ high spin: n = 4 → μ = √(4×6) = 4.90 BM

⚠️ Common Mistakes and Pitfalls

1. Electronic Configuration Errors

❌ Common Mistakes:
1. Wrong electronic configurations for transition metals
2. Not remembering exceptions (Cr, Cu)
3. Wrong oxidation state assignments
4. Incorrect d-electron counting
5. Not considering ligand field strength

✅ Correct Approach:
- Learn general patterns and exceptions
- Calculate oxidation states systematically
- Count d-electrons after removing electrons
- Consider weak vs strong field ligands

2. Crystal Field Theory Misapplications

❌ Misconceptions:
1. Wrong splitting patterns
2. Incorrect CFSE calculations
3. Not considering pairing energy
4. Wrong high spin vs low spin predictions
5. Ignoring spectrochemical series

✅ Clarifications:
- Use correct splitting diagrams
- Include pairing energy when necessary
- Consider both d-electron count and ligand strength
- Apply spectrochemical series correctly

📈 Year-wise Analysis Summary

Difficulty Distribution (2009-2024)

Topic-wise Weightage

🎯 Preparation Strategy

1. Study Approach

📚 Phase 1: Foundation (2 weeks)
- Electronic configurations of d and f block elements
- General properties of transition elements
- Basic terminology of coordination compounds
- Werner's theory basics

📚 Phase 2: Advanced Concepts (3 weeks)
- Crystal field theory and applications
- Valence bond theory
- Magnetic properties and calculations
- Spectrochemical series
- Types of isomerism

📚 Phase 3: Practice and Application (2 weeks)
- Previous year questions
- CFSE calculations
- Magnetic moment calculations
- Complex nomenclature
- Structure determination

2. Practice Schedule

📅 Daily Practice:
- Electronic configuration questions: 2-3
- Coordination compound questions: 4-5
- CFT calculation questions: 3-4
- Magnetic property questions: 2-3

📊 Weekly Targets:
- Total questions: 60-70
- Accuracy: 62%
- Time management: 3.5 hours
- Concept revision: All topics

💡 Success Tips

1. Memory Techniques

🧪 Mnemonics for Configurations:
- "Cr Cu Mo Ag" - Elements with d¹s¹ configuration
- "CFFS" - Crystal Field: Factors (oxidation state, period, ligands)
- "LIST" - Linkage, Ionization, Solvate, Coordination isomerism

📊 Visual Aids:
- d-orbital splitting diagrams
- Crystal field splitting patterns
- Coordination geometry models
- Isomerism type flowcharts

2. Problem-Solving Strategy

🎯 Step-by-Step Approach:
1. Identify central metal and oxidation state
2. Determine d-electron configuration
3. Identify ligands and their field strength
4. Determine geometry based on coordination number
5. Apply appropriate bonding theory
6. Calculate required properties (CFSE, magnetic moment)
7. Check for special cases (Jahn-Teller, EAN rule)

🔬 Laboratory and Industrial Applications

1. Laboratory Preparation

🧪 Important Complex Preparations:
- [Cu(NH₃)₄]SO₄·H₂O: Tetraamminecopper(II) sulfate
- [Co(NH₃)₆]Cl₃: Hexaamminecobalt(III) chloride
- K₃[Fe(CN)₆]: Potassium ferricyanide
- K₄[Fe(CN)₆]: Potassium ferrocyanide

2. Industrial Applications

🏭 Major Applications:
- Catalysis: Haber process, contact process
- Metallurgy: Extraction and purification
- Medicine: Platinum complexes in chemotherapy
- Photography: Silver complexes
- Analytical chemistry: Complexometric titrations
- Materials: Magnetic materials, pigments

🏆 Key Takeaways

1. Essential Concepts

✅ Must Know:
- Electronic configurations of d and f block elements
- Important exceptions and their reasons
- Coordination compound terminology
- Crystal field theory and applications
- Magnetic property calculations
- Types of isomerism in coordination compounds

✅ Must Practice:
- Electronic configuration problems
- CFSE calculations for different complexes
- Magnetic moment calculations
- Complex nomenclature and structure determination
- Isomer identification and analysis

2. Exam Strategy

🎯 During Exam:
- Identify metal oxidation state quickly
- Determine d-electron configuration
- Consider ligand field strength
- Apply appropriate bonding theory
- Calculate systematically (CFSE, magnetic moment)
- Check for special cases and exceptions

📊 Success Metrics:
- Accuracy: >62%
- Speed: <2.8 minutes/question
- Concept coverage: 100%
- Calculation accuracy: 80%

Master D and F Block Elements and Coordination Compounds with this comprehensive PYQ compilation! 🎯

This chapter combines theoretical concepts with numerical calculations. Systematic approach and regular practice are essential for success. 🚀

📚 Happy Learning and Best of Luck for Your JEE Preparation! 🌟