Crystal Field Theory - Octahedral and Tetrahedral - UNSOLVED PRACTICE SET
Chapter: Coordination Compounds | Topic: Crystal Field Theory Octahedral and Tetrahedral
CRYSTAL FIELD THEORY - OCTAHEDRAL AND TETRAHEDRAL - UNSOLVED PRACTICE SET
Topic: Crystal Field Theory Octahedral and Tetrahedral
Multiple Choice Questions
Q1. In an octahedral crystal field, the d-orbitals split into:
- Three orbitals of lower energy and two of higher energy
- Two orbitals of lower energy and three of higher energy
- All five orbitals of equal energy
- Four orbitals of lower energy and one of higher energy
Q2. The energy difference between t₂g and eg sets in an octahedral field is called:
- Crystal field splitting energy (Δ₀)
- Pairing energy (P)
- Exchange energy
- Lattice energy
Q3. In a tetrahedral crystal field, the splitting pattern is:
- The same as octahedral but with larger Δ
- The same as octahedral but with smaller Δ
- Reverse of octahedral with smaller Δ
- Reverse of octahedral with larger Δ
Q4. For the same metal and ligands, the relationship between octahedral and tetrahedral splitting is approximately:
- Δt = Δ₀
- Δt = (4/9)Δ₀
- Δt = 2Δ₀
- Δt = (9/4)Δ₀
Q5. In an octahedral field, the t₂g orbitals are:
- dx²-y² and dz²
- dxy, dyz, and dzx
- dx²-y², dxy, and dz²
- dyz, dzx, and dx²-y²
Q6. Strong field ligands cause:
- Small crystal field splitting
- Large crystal field splitting
- No crystal field splitting
- Equal splitting in all geometries
Short Answer Questions
Q7. Explain the splitting of d-orbitals in an octahedral crystal field. Which orbitals are raised in energy and which are lowered?
Q8. Why is the crystal field splitting energy (Δ₀) larger for strong field ligands than for weak field ligands?
Q9. In a tetrahedral complex, why is the crystal field splitting opposite to that in an octahedral complex? Explain with a diagram description.
Q10. What is meant by the spectrochemical series? Arrange the following ligands in increasing order of crystal field splitting ability: I⁻, H₂O, NH₃, CN⁻, Cl⁻.
Q11. Explain why tetrahedral complexes are rarely low-spin (inner orbital) complexes.
Q12. Draw a rough crystal field splitting diagram for d⁴ configuration in an octahedral field for both strong field and weak field cases. Label the electron distribution.
Long Answer Questions
Q13. Explain Crystal Field Theory for octahedral complexes. Discuss:
(a) The splitting of d-orbitals in an octahedral field
(b) The difference between strong field and weak field ligands
(c) How CFT explains the formation of high-spin and low-spin complexes
Illustrate with examples.
Q14. (a) Explain the splitting of d-orbitals in a tetrahedral crystal field. Why is Δt smaller than Δ₀?
(b) Why are tetrahedral complexes generally high-spin? Explain using the concepts of Δt and pairing energy.
(c) Give an example of a tetrahedral complex and predict whether it will be coloured or colourless.
Q15. (a) Compare crystal field splitting in octahedral and tetrahedral complexes with respect to:
(i) The pattern of splitting
(ii) The magnitude of splitting
(iii) The possibility of high-spin and low-spin complexes
(b) For a d⁶ configuration, draw the crystal field splitting diagrams for:
(i) High-spin octahedral complex
(ii) Low-spin octahedral complex
(iii) Tetrahedral complex
Numerical / Application-Based Problems
Q16. The crystal field splitting energy Δ₀ for [Ti(H₂O)₆]³⁺ is 20,300 cm⁻¹.
(a) Calculate the wavelength of light absorbed by this complex.
(b) Predict the colour of the complex. (Hint: The colour observed is complementary to the colour absorbed.)
(c) Why does this complex show only one d-d transition?
(d) If the ligand is changed from H₂O to CN⁻, would Δ₀ increase or decrease? Explain.
Q17. Consider the following octahedral complexes:
[CoF₆]³⁻: High spin, Δ₀ = 13,000 cm⁻¹
[Co(NH₃)₆]³⁺: Low spin, Δ₀ = 23,000 cm⁻¹
[Co(CN)₆]³⁻: Low spin, Δ₀ = 34,000 cm⁻¹
(a) For each complex, show the electron distribution in t₂g and eg orbitals.
(b) Calculate the crystal field stabilization energy (CFSE) for each complex.
(c) Explain why F⁻ forms a high-spin complex while CN⁻ forms a low-spin complex with Co³⁺.
(d) Arrange these ligands in the spectrochemical series based on the given data.
Q18. In a school laboratory, students are given four solutions containing different octahedral complexes of Co³⁺:
Solution A: [CoF₆]³⁻ — green
Solution B: [Co(H₂O)₆]³⁺ — blue
Solution C: [Co(NH₃)₆]³⁺ — yellow
Solution D: [Co(CN)₆]³⁻ — colourless
(a) Explain the origin of colour in these complexes using CFT.
(b) Arrange these complexes in order of increasing crystal field splitting energy (Δ₀). Give reasoning.
(c) Why is [Co(CN)₆]³⁻ colourless? Explain using the concept of d-d transitions.
(d) If you were to replace Co³⁺ with Fe²⁺ (d⁶) in an octahedral field with NH₃ ligands, would you expect a high-spin or low-spin complex? Explain using CFT.