This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Bonding in Coordination Compounds – 1”.
1. Which of the following does not explain the nature of bonding in coordination compounds?
a) Crystal Field Theory
b) Molecular Orbital Theory
c) Valence Bond Theory
d) VSEPR Theory
Explanation: The VSEPR Theory explains the structure of individual molecules based on the electron pairs in their atoms. VBT, CFT, LFT and MOT are theories that explain the nature of bonding in coordination compounds.
2. How many types of hybridisation are possible for complexes with a coordination number of 4?
Explanation: According to VBT, a complex with CN=4 can have two possible types of hybridisation and hence geometries. The sp3 hybridisation results in tetrahedral geometry and dsp2 hybridisation results in square planar geometry.
3. How many empty orbitals are available in the central metal ion of a complex that has a trigonal bipyramidal geometry?
Explanation: One of the assumptions of VBT is that the number of empty orbitals in the metal ion for making bonds with the ligands is equal to its CN. A trigonal bipyramidal geometry has a hybridisation of sp3d and hence a CN=5.
4. A complex having _________ geometry can have more than one type of hybridisation.
b) square planar
c) trigonal bipyramidal
Explanation: Complexes having octahedral geometry can have either sp3d2 or d2sp3 hybridisation depending on whether the outer or inner d orbitals are involved in hybridisation respectively.
5. Which statement regarding [Cr(NH3)6]3+ is incorrect?
a) It has octahedral geometry
b) It has d2sp3 hybridisation
c) It is diamagnetic
d) It is a low spin complex
Explanation: Cr3+ has six empty orbitals- two 3d, one 4s and three 4p orbitals, which are occupied by six electron pairs from six NH3 molecules to form six d2sp3 hybridised orbitals. This leaves, three unpaired 3d electrons, making it paramagnetic. Also, since the inner d orbitals are involved, it is a low spin complex.
6. The ferricyanide complex ion is _________
b) outer orbital
c) spin free
Explanation: The oxidation state of Fe in [Fe(CN)6]3- ion is +3, which leaves it with five unpaired electrons in 3d orbitals. Two of these pair up leaving one unpaired electron in 3d and six vacant orbitals to form d2sp3 hybridised octahedral inner orbital complex.
7. What is the number of unpaired electrons in [Fe(H2O)6]2+ if it is known to be a high spin complex?
Explanation: The configuration of Fe2+ is 3d6. The complex has a CN=6 has should have sp3d2 hybridisation. This leaves the 3d orbitals as it is with 4 unpaired electrons.
Explanation: There is one unpaired electron in the 3d orbitals. The presence of unpaired electrons makes a complex paramagnetic. In this case, since only 1 unpaired electron is present, it is a weak paramagnet.
9. Coordination entities with only three ligand groups attached to the metal ion can have d2sp3 hybridisation.
Explanation: This happens in the case of didentate ligands which have six pairs of electrons from three molecules. For example, [Co(ox)3]3- has d2sp3 hybridisation and is diamagnetic.
10. Identify the correct geometry and magnetic behaviour of the complex from the configuration shown.
a) Square planar, diamagnetic
b) Square planar, paramagnetic
c) Tetrahedral, diamagnetic
d) Tetrahedral, paramagnetic
Explanation: The hybridisation type of the complex is dsp2 which corresponds to square planar geometry. Because there are no unpaired electrons, it is diamagnetic.
Explanation: The hybridisation type is sp which involves only two orbitals, so the geometry has to be linear and the coordination number is 2.
12. [Co(en)2(NH3)Cl]2+ is known to be a diamagnetic complex. What is the type of hybridisation it shows?
Explanation: Co3+ has 3d6 configuration. For a complex to be diamagnetic, it should have no unpaired electrons. So, the single electrons in the 3d orbital will have to pair up and form 3 pairs leaving two 3d orbitals vacant. This results in d2sp3 hybridisation.
13. The compound K4[Mn(CN)6] is diamagnetic.
Explanation: The atomic number of Mn is 25 and the outer shell configuration of Mn2+ is 3d5. Four out of these five electrons pair up leaving 1 unpaired electron in 3d orbital and forming d2sp3 hybridisation. Thus, it is paramagnetic.
14. Identify the incorrect statement regarding VBT.
a) It does not explain the colour of coordination compounds
b) It is unreliable in the prediction of geometries of 4-coordinate complexes
c) It does not explain the kinetic stabilities of coordination compounds
d) It can distinguish between strong and weak ligands
Explanation: One of the limitations of VBT is that it cannot differentiate between weak and strong ligands. The other options are also its limitations.
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