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Solved Practice Questions: Crystal field Theory | Inorganic Chemistry PDF Download

Q.1. Based on crystal field theory, write the electronic configuration of d4 in terms of t2g and eg in an octahedral field when Δ0 > P.

The magnitude of Δ0 decides the actual configuration of d-orbitals with the help of mean pairing energy.
If P > Δ0, then pairing of electrons does not occur, and electrons enter the higher energy orbitals and thus form high spin complexes due to weak-field ligands. Therefore, one electron enters in eg orbital and 3 electrons in t2g with configuration t2g3 eg1.


Q.2. How does the magnitude of Δ0 decide the actual configuration of d orbitals in a coordination entity?

If Δ0 is greater than the pairing energy, electrons get paired in lower energy d-orbitals giving a low spin complex. On the other hand, if Δ0 is, is less than the pairing energy, electrons occupy higher energy d-orbitals giving a high spin complex.


Q.3. If Δ0 is the octahedral crystal field splitting energy. Then what will be the CFSE for Fe(CN)6]4?

Fe is in +2 oxidation state, and therefore the configuration will be 3d6.
Since the ligand is a strong field ligand, the excitation energy is greater than the pairing energy. Therefore, the configuration is t2g6 eg0.
CFSE= 6 × (– 0.4Δ0) = – 2.4 Δ0.


Q.4. Explain by giving a suitable example for Crystal field splitting.

The presence of ligands causes the splitting of degenerate energy levels. When a ligand approaches a transition metal ion, the degenerate d-orbitals split into two sets, one with lower energy and one with higher energy which is referred to as crystal field splitting, and the difference between the lower and higher energy sets is referred to as crystal field splitting energy (CFSE).

Solved Practice Questions: Crystal field Theory | Inorganic Chemistry

Example: 3d5 of Mn2+


Q.5. State True or False.
Strong field ligands, such as CN usually produce low spin complexes and large crystal field splitting.

True, Strong field ligands, such as CN usually produce low spin complexes and large crystal field splitting.


Q.6. According to crystal field theory-
(a) The order of increasing field strength of ligands is F– > H2O > NH3.
(b) If pairing energy exceeds the magnitude of crystal field splitting, then pairing occurs.
(c) d4 to d7 coordination entities are more stable for the strong field than weak field cases.
(d) Tetrahedral complexes have sufficiently large splitting energy to force pairing, and therefore, high spin configurations are rarely observed.

dto d7 co-ordination entities are more stable for the strong field as compared to weak field cases.


Q.7. Which one of the following statements is FALSE?
(a) In an octahedral crystal field, the d electrons on a metal ion occupy the eg set of orbitals before occupying the t2g set of orbitals.
(b) Diamagnetic metal ions cannot have an odd number of electrons.
(c) Low spin complexes can be paramagnetic.
(d) In high spin octahedral complexes, Δoct is less than the electron pairing energy and is relatively very small.

In an octahedral crystal field, the d electrons on a metal ion occupy the eg set of orbitals before occupying the t2g set of orbitals.


Q.8. Which of the following compound is paramagnetic?
(a) Hexa amine chromium (III) ion
(b) Tetraamminezinc (II) ion
(c) Tetracyanonickelate (II) ion
(d) Diammine silver (I) ion

A complex is paramagnetic due to the presence of unpaired electrons. Chromium contains 3 unpaired electrons.


Q.9. Explain the violet colour of [Ti(H2O)6]3+ complex on the basis of the crystal field theory?

[Ti(H2O)6]3+ is an octahedral complex. The oxidation state of Ti is +3 with the coordination number 6.
Its outer electronic configuration is 3d1, which means that it has one unpaired electron. This unpaired electron is excited from t2g level to eg level by absorbing yellow light and hence appears violet coloured.


Q.10. How is the crystal field splitting energy for octahedral(Δ0) and tetrahedral (Δt) complexes related?

Splitting in tetrahedral complexes is 2/3rd of the octahedral complex.
Therefore, for one ligand splitting on octahedral

Solved Practice Questions: Crystal field Theory | Inorganic Chemistry
For one ligand splitting in tetrahedral is
Solved Practice Questions: Crystal field Theory | Inorganic Chemistry

Therefore, for four ligand,
Solved Practice Questions: Crystal field Theory | Inorganic Chemistry

The relationship of crystal field splitting energy for octahedral(Δ0) and tetrahedral (Δt) complexes is

Solved Practice Questions: Crystal field Theory | Inorganic Chemistry


Q.11. On the basis of crystal field theory, write the electronic configuration of din terms of t2g and eg in an octahedral field when Δ0 < P.

The magnitude of Δ0 decides the actual configuration of d-orbitals with the help of mean pairing energy.
If P < Δ0, then pairing of electrons occurs within the same set and forms low spin complexes due to strong-field ligands. Therefore, it becomes more energetically favourable for the fourth electron to occupy a t2g orbital with configuration t2g4 eg0.


Q.12. What are the limitations of crystal field theory?

The limitations of crystal field theory are as follows:

  • This theory is applicable to metal ions with d-orbitals and does not explain s- and p-orbitals.
  • It does not explain z bonding in the coordination compounds.
  • This theory considers electrostatic attraction between central metal ion and ligands, hence considering only ionic bonds between them but does not account for covalent nature between them or coordínate bonds.
  • Water (H2O) is a stronger ligand than OH, which this theory cannot explain satisfactorily.


Q.13. Fill in the blank.
The electronic configuration of the central atom is K4(Fe(CN)6] on crystal field theory is ___.

The electronic configuration of the central atom is K4(Fe(CN)6] on crystal field theory is t2g6eg0.


Q.14. What will be CFSE for the d6 high spin complex for both tetrahedral and octahedral complexes?
(a) 0.6, 0.6

(b) 0.4, 0.4
(c)  0.4, 0.6
(d) 0.6, 0.4

Correct Answer is Option (c)


Q.15. Crystal field stabilization energy for high spin d4 octahedral complex is:
(a) – 1.8 Δ0
(b) – 1.6 Δ0 + P
(c) –1.2 Δ0
(d) –0.6 Δ0

Correct Answer is Option (d)
Solved Practice Questions: Crystal field Theory | Inorganic Chemistry

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FAQs on Solved Practice Questions: Crystal field Theory - Inorganic Chemistry

1. What is crystal field theory?
Ans. Crystal field theory is a model that explains the behavior of transition metal complexes by considering the interaction between the metal ion and the ligands surrounding it. It focuses on the electrostatic interactions between the negatively charged ligands and the positively charged metal ion.
2. How does crystal field theory explain the color of transition metal complexes?
Ans. Crystal field theory explains the color of transition metal complexes by considering the splitting of d orbitals in the presence of ligands. When ligands approach the metal ion, the d orbitals split into two energy levels, with some orbitals becoming higher in energy (eg. dx2-y2, dz2) and others becoming lower in energy (eg. dxy, dxz, dyz). The energy difference between these levels corresponds to the absorption of certain wavelengths of light, resulting in the observed color.
3. What are crystal field splitting energy and crystal field stabilization energy?
Ans. Crystal field splitting energy (Δ) refers to the energy difference between the higher and lower energy d orbitals in a transition metal complex caused by the presence of ligands. It determines the color and magnetic properties of the complex. On the other hand, crystal field stabilization energy (CFSE) is the overall energy lowering that occurs when electrons occupy the lower energy orbitals. It is responsible for the stability and structural properties of the complex.
4. How does crystal field theory explain the magnetic properties of transition metal complexes?
Ans. Crystal field theory explains the magnetic properties of transition metal complexes based on the number and arrangement of unpaired electrons in the d orbitals. In octahedral complexes, if there are unpaired electrons in the higher energy orbitals, the complex is paramagnetic and attracted to a magnetic field. If all the d orbitals are completely filled or have paired electrons, the complex is diamagnetic and repelled by a magnetic field.
5. What are the limitations of crystal field theory?
Ans. Crystal field theory has some limitations. It does not consider the covalent bonding nature between the metal ion and the ligands, which can be significant in some complexes. It also does not account for the influence of solvent or temperature on the properties of the complexes. Additionally, crystal field theory cannot fully explain the electronic structure and spectroscopic properties of transition metal complexes, necessitating the use of more advanced theories like molecular orbital theory.
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