Lecture on Crystal Field Theory

Introduction

• Presenter: Chad from Chad's Prep
• Purpose: To simplify the learning of science, including high school, college, and standardized test prep (MCAT, DAT, OAT).
• Current Lesson: Part of the General Chemistry playlist.

Electron Configurations of Transition Metal Cations

Important Points

• Exceptions: Recall exceptions when dealing with electron configurations.
• Removing Electrons: Remove from the 4s orbital before the 3d orbital when forming cations.

Examples:

1. Scandium (Sc)
   • Neutral: [Ar] 4s^2 3d^1
   • Sc^3+: Remove three electrons; result is [Ar], D0 metal.
2. Iron (Fe)
   • Neutral: [Ar] 4s^2 3d^6
   • Fe^3+: Remove 3 electrons; result is [Ar] 3d^5, has 5 d-electrons.
3. Manganese (Mn)
   • Neutral: [Ar] 4s^2 3d^5
   • Mn^2+: Remove 2 electrons; result is [Ar] 3d^5, 5 d-electrons.
4. Chromium (Cr)
   • Exception: [Ar] 4s^1 3d^5 (more stable half-filled subshells).
   • Cr^3+: Result is [Ar] 3d^3.
5. Copper (Cu)
   • Exception: [Ar] 4s^1 3d^{10} (full 3d subshell, half-filled 4s subshell).
   • Cu^+: Result is [Ar] 3d^{10}.

Crystal Field Theory

• D Orbitals in Transition Metals:
  • Types: dxy, dyz, dxz, dx²-y², dz².
  • Orbital Orientation: Important for ligand interactions.
  • dxy, dyz, dxz: Electron density between axes.
  • dx²-y², dz²: Electron density on axes.

Ligand Binding

• Octahedral Complexes: Ligands bind on axes (affects dx²-y², dz²).
• Tetrahedral Complexes: Ligands bind between axes (affects dxy, dyz, dxz).

Energy Splitting

• Crystal Field Splitting Energy (Δ or Δ₀): Difference between split energy levels.
• High Spin vs Low Spin:
  • High Spin: Large number of unpaired electrons, smaller Δ.
  • Low Spin: Smaller number of unpaired electrons, larger Δ.

Ligand Influence

• Spectrochemical Series: Determines ligand field strength.
• Strong Field Ligands: Large Δ, lead to low spin configurations.
• Weak Field Ligands: Small Δ, lead to high spin configurations.

Splitting Patterns

• Octahedral:
  • High Spin: Different electron arrangement in d-orbitals.
  • Low Spin: Different electron arrangement.
• Tetrahedral: Always high spin.
• Square Planar: Unique to D8 systems (e.g., Ni²⁺, Pt²⁺), dsp² hybridization.

Hybridization

• Octahedral:
  • Low Spin: d²sp³
  • High Spin: sp³d²
• Square Planar: dsp² hybridization, involves empty d-orbitals.

Conclusion

• Next Lesson: Discussion on phenomena explained by crystal field theory—color and magnetism.
• Recommendations: Check out Chad’s Gen Chem Master Course for final exam prep with rapid reviews and practice exams.

Additional Resources

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