chemistry : class11 Crystal-Field Orbital Orientation : Shapes of d orbitals : Structure of Atom MCQ Questions and Answers
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Crystal-Field Orbital Orientation
MCQ questions and answers.
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MCQ Questions
1. In an ideal octahedral crystal field with six ligands directed along the positive and negative x-, y-, and z-axes, which d orbitals experience the greatest direct electrostatic repulsion?
A.
dxy and dyz
B.
dxz and dxy
C.
dx2-y2 and dz2
D.
All five d orbitals equally
Correct Answer:
dx2-y2 and dz2
Explanation:
The lobes of dx2-y2 point directly along the x- and y-axes, while dz2 points along the z-axis. Therefore, both orbitals point directly toward the six octahedral ligands and experience maximum repulsion.
2. For an octahedral complex whose ligands approach along the Cartesian axes, which statement correctly describes the orientation of the t2g orbitals?
A.
Their lobes point directly at the ligands
B.
Their lobes lie between the ligand directions
C.
Their lobes point only along the z-axis
D.
Their lobes are directed toward the centers of the octahedral faces
Correct Answer:
Their lobes lie between the ligand directions
Explanation:
The dxy, dyz, and dxz orbitals have lobes between the x, y, and z axes. Since octahedral ligands lie on these axes, t2g orbitals avoid direct ligand directions and experience less repulsion.
3. In a tetrahedral crystal field, four ligands are directed approximately toward alternating corners of a cube. Which set of d orbitals points more nearly toward the ligand directions?
A.
dxy, dyz, and dxz
B.
dx2-y2 and dz2
C.
Only dz2
D.
All five d orbitals equally
Correct Answer:
dxy, dyz, and dxz
Explanation:
In a tetrahedral arrangement, ligands approach between the Cartesian axes. The lobes of dxy, dyz, and dxz are oriented between axes and therefore point more nearly toward the ligand directions.
4. Why is the relative crystal-field orientation of the d orbitals reversed in a tetrahedral field compared with an octahedral field?
A.
Tetrahedral complexes contain p orbitals instead of d orbitals
B.
The ligands in a tetrahedral field approach between the coordinate axes rather than along them
C.
The dz2 orbital disappears in tetrahedral symmetry
D.
The d orbitals rotate into s orbitals in a tetrahedral field
Correct Answer:
The ligands in a tetrahedral field approach between the coordinate axes rather than along them
Explanation:
Octahedral ligands lie along the axes, directly opposing dx2-y2 and dz2. Tetrahedral ligands lie between the axes, making dxy, dyz, and dxz more directly oriented toward ligand directions.
5. A square-planar complex has four ligands located along the positive and negative x- and y-axes in the xy-plane. Which orbital has the strongest direct repulsion from these ligands?
A.
dz2
B.
dxy
C.
dx2-y2
D.
dxz
Correct Answer:
dx2-y2
Explanation:
The four lobes of dx2-y2 point directly along the x- and y-axes, exactly toward the four square-planar ligands. It therefore experiences the strongest direct electrostatic repulsion.
6. For the same square-planar arrangement, which d orbital has lobes that point between the directions of the four ligands and therefore avoids direct ligand alignment in the xy-plane?
A.
dx2-y2
B.
dxy
C.
dz2
D.
d xz
Correct Answer:
dxy
Explanation:
The dxy lobes lie between the x- and y-axes, whereas square-planar ligands lie on those axes. Thus dxy does not point directly toward the ligands in the xy-plane.
7. Which comparison correctly relates orbital orientation in octahedral and square-planar fields when the four equatorial ligands occupy the x- and y-axis directions?
A.
dx2-y2 points directly toward the equatorial ligands in both fields
B.
dxy points directly toward the equatorial ligands in both fields
C.
dz2 points directly toward all four equatorial ligands in both fields
D.
dxz points directly toward the equatorial ligands in both fields
Correct Answer:
dx2-y2 points directly toward the equatorial ligands in both fields
Explanation:
In both octahedral and square-planar arrangements, the equatorial ligands lie along the x- and y-axes. The dx2-y2 lobes are directed along these axes and therefore point directly toward those ligands.
8. A ligand approaches a metal ion along the positive z-axis. Which d orbital has a lobe directed most directly toward this ligand?
A.
dxy
B.
dxz
C.
dx2-y2
D.
dz2
Correct Answer:
dz2
Explanation:
The dz2 orbital has two major lobes oriented along the positive and negative z-axis. A ligand on the positive z-axis therefore lies directly along one of its lobes.
9. Which orbital is least likely to undergo strong direct sigma-type interaction with ligands placed along the x-, y-, and z-axes in an octahedral complex?
A.
dx2-y2
B.
dz2
C.
dxy
D.
Both dx2-y2 and dz2
Correct Answer:
dxy
Explanation:
The dxy lobes lie between the x- and y-axes, so they do not point directly toward any of the six axial ligand directions. This minimizes direct sigma overlap compared with orbitals oriented along the axes.
10. In an ideal tetrahedral field, which orientation-based explanation accounts for the lower electrostatic repulsion of dx2-y2 and dz2 relative to dxy, dyz, and dxz?
A.
dx2-y2 and dz2 have no angular dependence
B.
dx2-y2 and dz2 point more nearly between the tetrahedral ligand directions
C.
dx2-y2 and dz2 are spherically symmetric
D.
dx2-y2 and dz2 are located outside the metal ion
Correct Answer:
dx2-y2 and dz2 point more nearly between the tetrahedral ligand directions
Explanation:
Tetrahedral ligands approach between the Cartesian axes. The dx2-y2 and dz2 lobes are oriented mainly along the axes, so they lie farther from the ligand directions and experience less direct repulsion.
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