Valence Bond Theory in Coordination Compounds - UNSOLVED PRACTICE SET

Q7. What is the difference between inner orbital and outer orbital complexes? Give one example of each.

Q8. Explain why [CoF₆]³⁻ is paramagnetic while [Co(NH₃)₆]³⁺ is diamagnetic, even though both contain Co³⁺ ion.

Q9. Predict the hybridization, geometry, and magnetic nature of [Ni(CO)₄]. (Atomic number of Ni = 28)

Q10. What is meant by "hybridization" in the context of VBT applied to coordination compounds? How does it determine the geometry of the complex?

Q11. [Fe(H₂O)₆]²⁺ is paramagnetic with 4 unpaired electrons, while [Fe(CN)₆]⁴⁻ is diamagnetic. Explain this difference using VBT.

Q12. Why does VBT fail to explain the colour of coordination compounds? Mention one other limitation.

Q13. Explain the application of Valence Bond Theory to coordination compounds. Discuss how VBT explains:

(a) The geometry of complexes

(b) Magnetic properties

(c) The distinction between inner and outer orbital complexes

Illustrate with suitable examples.

Q14. (a) Explain the bonding in [Ni(CN)₄]²⁻ using VBT. Show why it is square planar and diamagnetic.

(b) Compare this with [NiCl₄]²⁻, which is tetrahedral and paramagnetic. Explain the difference in terms of ligand field strength.

Q15. (a) Apply VBT to explain the formation of [Co(NH₃)₆]³⁺ and [CoF₆]³⁻.

(b) For each complex, determine:

(i) The hybridization

(ii) Whether it is inner or outer orbital

(iii) The number of unpaired electrons

(iv) The magnetic nature

(v) The geometry

(c) What does the difference between these two complexes tell you about the nature of NH₃ and F⁻ as ligands?

Q16. Consider the following complexes of iron:

Complex A: [Fe(H₂O)₆]²⁺ — magnetic moment = 4.9 BM

Complex B: [Fe(CN)₆]⁴⁻ — magnetic moment = 0 BM

Complex C: [FeF₆]³⁻ — magnetic moment = 5.9 BM

(Atomic number of Fe = 26)

(a) Determine the number of unpaired electrons in each complex using the spin-only formula: μ = √[n(n+2)] BM.

(b) Predict the hybridization in each complex (inner or outer orbital).

(c) Draw the orbital diagrams for the metal ion in each complex showing electron distribution.

(d) Classify each ligand (H₂O, CN⁻, F⁻) as strong-field or weak-field.

(e) Explain why the same metal ion (Fe) shows different hybridizations with different ligands.

Q17. A student is studying nickel complexes in the laboratory:

[Ni(CO)₄]: Tetrahedral, diamagnetic

[Ni(CN)₄]²⁻: Square planar, diamagnetic

[NiCl₄]²⁻: Tetrahedral, paramagnetic (2 unpaired electrons)

(Atomic number of Ni = 28)

(a) Explain the bonding in each complex using VBT. Show the hybridization in each case.

(b) Draw the orbital diagram for Ni²⁺ and show how hybridization occurs in [Ni(CN)₄]²⁻.

(c) Why does CO cause pairing of electrons while Cl⁻ does not?

(d) Calculate the magnetic moment of [NiCl₄]²⁻ using the spin-only formula and verify it matches the experimental value.

Q18. In your school chemistry project, you are asked to prepare models of coordination compounds and explain their bonding using VBT. You choose to study [Cr(NH₃)₆]³⁺ and [Cr(H₂O)₆]³⁺.

(a) Write the electronic configuration of Cr³⁺ ion.

(b) Predict the hybridization, geometry, and magnetic nature of both complexes.

(c) Both complexes are coloured. Can VBT explain their colour? Give reason.

(d) The magnetic moment of [Cr(NH₃)₆]³⁺ is 3.87 BM. Verify this using the spin-only formula.

(e) Your classmate claims that [Cr(NH₃)₆]³⁺ should be an outer orbital complex because Cr³⁺ has only 3 d-electrons. Is this correct? Explain.