CBSE 2024 · Region 1 · Set 1 · Q30 · 4 marks
The Valence Bond Theory (VBT) explains the formation, magnetic behaviour and geometrical shapes of coordination compounds whereas 'The Crystal Field Theory' for coordination compounds is based on the effect of different crystal fields (provided by ligands taken as point charges), on the degeneracy of d-orbital energies of the central metal atom/ion. The splitting of the d-orbitals provides different electronic arrangements in strong and weak crystal fields. The crystal field theory attributes the colour of the coordination compounds to d-d transition of the electron. Coordination compounds find extensive applications in metallurgical processes, analytical and medicinal chemistry. Answer the following questions :(a)What is crystal field splitting energy ?(b)Give reason for the violet colour of the complex $\displaystyle \left[\mathrm{Ti}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}$ on the basis of crystal field theory.$\displaystyle \left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}$ is paramagnetic while $\displaystyle \left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}$ is diamagnetic. Explain why. [Atomic No. : $\displaystyle \mathrm{Cr}=24, \mathrm{Ni}=28$ ]Explain why $\displaystyle \left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}$ is an inner orbital complex, whereas $\displaystyle \left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}$ is an outer orbital complex. [Atomic No. : $\displaystyle \mathrm{Fe}=26$ ]
The Valence Bond Theory (VBT) explains the formation, magnetic behaviour and geometrical shapes of coordination compounds whereas 'The Crystal Field Theory' for coordination compounds is based on the effect of different crystal fields (provided by ligands taken as point charges), on the degeneracy of d-orbital energies of the central metal atom/ion. The splitting of the d-orbitals provides different electronic arrangements in strong and weak crystal fields. The crystal field theory attributes the colour of the coordination compounds to d-d transition of the electron. Coordination compounds find extensive applications in metallurgical processes, analytical and medicinal chemistry. Answer the following questions :
(a)
What is crystal field splitting energy ?
(b)
Give reason for the violet colour of the complex $\displaystyle \left[\mathrm{Ti}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}$ on the basis of crystal field theory.
$\displaystyle \left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}$ is paramagnetic while $\displaystyle \left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}$ is diamagnetic. Explain why. [Atomic No. : $\displaystyle \mathrm{Cr}=24, \mathrm{Ni}=28$ ]
Explain why $\displaystyle \left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}$ is an inner orbital complex, whereas $\displaystyle \left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}$ is an outer orbital complex. [Atomic No. : $\displaystyle \mathrm{Fe}=26$ ]
Marking-scheme solution
(a) The energy used in the splitting of degenerate d- orbitals due to the presence of ligands in a definite geometry is called Crystal Field Splitting Energy.
(b) \(\displaystyle \mathrm{Ti}^{3+}=3 \mathrm{~d}^{1}\) i.e. \(\displaystyle t_{2 g}{ }^{1} e_{g}^{0}\) Due to d - d transition.
(c) 
Due to stable \(\displaystyle t_{2 g}{ }^{3}\) configuration, henceparamagnetic.
\(\displaystyle \mathrm{CN}^{-}\)being strong field ligand pair up the electrons and hence diamagnetic. ORCoordination CompoundsBonding in Coordination CompoundsUnderstandcase_studyhard
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CBSE Class 12 Chemistry past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.