Chemistry Class 12 NCERT Solutions: Chapter 9 Coordination Compounds Part 7 (For CBSE, ICSE, IAS, NET, NRA 2023)

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Q: 16. Draw figure to show the splitting of d orbitals in an octahedral crystal field.


Q_16_The Splitting of D Orbitals in an Octahedral Crystal Fi …

The splitting of the d orbitals in an octahedral field takes place in such a way that , experience a rise in energy and form the level, while , experience a fall in energy and form the level.

Q: 17. What is spectrochemical series? Explain the difference between a weak field ligand and strong field ligand.


A spectrochemical series is the arrangement of common ligands in the increasing order of their crystal (field splitting energy (CFSE) values. The ligands present on the So the series are strong field ligands while that on the L. H. S are weak field ligands. Also strong field ligands cause higher splitting in the d orbitals than weak field ligands.

Q: 18. What is crystal field splitting energy? How does the magnitude of decide the actual configuration of d-orbitals in a coordination entity?


The degenerate d (orbitals (in a spherical field environment) split into two levels i.e.. , eg and in the presence of ligands. The splitting of the degenerate levels due to the presence of ligands is called the crystal (field splitting while the energy difference between the two levels is called the crystal (field splitting energy. It is denoted by .

After the orbitals have split, the filling of the electrons takes place. After electron (each) has been filled in the three orbitals, the filling of the fourth electron takes place in two ways. It can enter the eg orbital (giving rise to like electronic configuration) or the pairing of the electrons can take place in the orbitals (giving rise to like electronic configuration) . If the value of a ligand is less than the pairing energy (P) , then the electrons enter the orbital. On the other hand, if the value of a ligand is more than the pairing energy (P) , then the electrons enter the orbital.

Q: 19. is paramagnetic wile is diamagnetic. Explain why?


Cr is in the + 3 oxidation state i.e.. , configuration. Also, is a weak field ligand that does not cause the pairing of the electrons in the orbital.

Q_19_Pairing of the Electrons

Therefore, it undergoes hybridization and the electrons in the orbitals remain unpaired. Hence, it is paramagnetic in nature. In exists in the oxidation state i.e.. , configuration.

Q_19_1_The + 2 Oxidation State

is a strong field ligand. It causes the pairing of the orbital electrons. Then, undergoes hybridization.

Q_19_1_The 3d Orbital Electrons

As there are no unpaired electrons, it is diamagnetic.

Q: 20. A solution of is green but a solution of is colourless. Explain.


In is a weak field ligand. Therefore, there are unpaired electrons in Ni2 + . In this complex, the d electrons from the lower energy level can be excited to the higher energy level i.e.. , the possibility of transition is present. Hence, is coloured.

In , the electrons are all paired as is a strong field ligand. Therefore, d-d transition is not possible in . Hence, it is colourless.

Q: 21. are of different colours in dilute solutions. Why?


The colour of a particular coordination compound depends on the magnitude of the crystal-field splitting energy, . This in turn depends on the nature of the ligand. case of , the colour differs because there is a difference I the . Now, is a strong field ligand having a higher value as compared the value of water. This means that the absorption of energy for the intra transition also differs. Hence, the transmitted colour also differs.