DTM

الامتياز في الكيمياء

by Emtiazche · 10 questions · 0 saves · 0 likes
Play in QuizPilot
#1
1) In coordination chemistry, what does the term 'الامتياز' (ligand field splitting) primarily refer to?
  1. The energy separation of d-orbitals in a transition metal due to ligand interactions
  2. The bond dissociation energy of metal–ligand bonds
  3. The difference in electronegativity between metal and ligand atoms
  4. The energy difference between sigma and pi bonds formed with ligands
Show answer
The energy separation of d-orbitals in a transition metal due to ligand interactions
#2
2) Which factor most directly increases the magnitude of d-orbital splitting (Δ) in an octahedral complex?
  1. Using strong-field ligands such as CN− or CO
  2. Using ligands lower in the spectrochemical series
  3. Decreasing the oxidation state of the central metal
  4. Increasing the metal–ligand bond distance
Show answer
Using strong-field ligands such as CN− or CO
#3
3) For a d6 metal ion in an octahedral field, which situation favors a low-spin configuration?
  1. High temperature and high spin–orbit coupling
  2. Small Δ and weak-field ligands, leading to high pairing energy
  3. Presence of paramagnetic ligands that donate unpaired electrons
  4. Large Δ relative to pairing energy, causing electrons to pair in lower orbitals
Show answer
Large Δ relative to pairing energy, causing electrons to pair in lower orbitals
#4
4) How does a tetrahedral ligand field splitting (Δt) generally compare numerically to the octahedral splitting (Δo) for the same metal–ligand combination?
  1. Δt is always larger than Δo due to increased electrostatic interactions
  2. Δt is generally smaller, roughly 4/9 of Δo
  3. Δt is approximately equal to 2 × Δo
  4. Δt is zero because tetrahedral fields do not split d-orbitals
Show answer
Δt is generally smaller, roughly 4/9 of Δo
#5
5) Which experimental technique directly measures the ligand field splitting energy in many transition-metal complexes?
  1. Nuclear magnetic resonance (NMR) chemical shifts
  2. UV-Vis (electronic) spectroscopy observing d–d transitions
  3. Mass spectrometry of the intact complex
  4. Infrared spectroscopy of ligand vibrations
Show answer
UV-Vis (electronic) spectroscopy observing d–d transitions
#6
6) In crystal field theory, which set of d-orbitals is higher in energy in an octahedral field?
  1. Core s and p orbitals are higher than d-orbitals
  2. eg (dz2, dx2−y2)
  3. All five d-orbitals remain degenerate
  4. t2g (dxy, dxz, dyz)
Show answer
eg (dz2, dx2−y2)
#7
7) Which of the following modifications to a complex would most likely decrease the observed ligand field splitting Δo?
  1. Substituting strong σ-donor/π-acceptor ligands with weak σ-donors
  2. Increasing the oxidation state of the metal center
  3. Replacing H2O ligands with CN− ligands
  4. Replacing a 3d metal with a 4d or 5d metal of similar charge
Show answer
Substituting strong σ-donor/π-acceptor ligands with weak σ-donors
#8
8) What role does π-backbonding play in modifying ligand field splitting for complexes with π-acceptor ligands?
  1. It increases splitting by withdrawing electron density from metal eg orbitals only
  2. It reduces splitting by donating electron density into metal t2g orbitals
  3. It has no effect because π-backbonding involves only ligand-centered orbitals
  4. It can increase Δ by stabilizing t2g orbitals through back-donation into ligand π* orbitals
Show answer
It can increase Δ by stabilizing t2g orbitals through back-donation into ligand π* orbitals
#9
9) Which statement best distinguishes crystal field theory (CFT) from ligand field theory (LFT)?
  1. LFT includes covalent metal–ligand interactions and orbital mixing; CFT is purely electrostatic
  2. They are identical theories with different names
  3. CFT accounts for covalency while LFT treats ligands as point charges exclusively
  4. CFT is a quantum mechanical method while LFT is a classical model
Show answer
LFT includes covalent metal–ligand interactions and orbital mixing; CFT is purely electrostatic
#10
10) For a complex showing an intense absorption band due to charge-transfer rather than a weak d–d transition, what does this imply about ligand field splitting and selection rules?
  1. Δ is very large so that d–d transitions are forbidden by spin selection only
  2. Charge-transfer transitions often have higher intensity and can overshadow weak parity-forbidden d–d bands
  3. d–d transitions are always more intense than charge-transfer bands
  4. It implies the complex has no unpaired electrons
Show answer
Charge-transfer transitions often have higher intensity and can overshadow weak parity-forbidden d–d bands
Play in QuizPilot