Molecular Orbital Theory for Sigma and Pi Bonds

Introduction to Molecular Orbital Theory

• Focus on understanding key concepts without delving into complex math and physics.
• Atomic Orbitals: Indicate electron locations on individual atoms, with types including sp3, sp2, sp, and p orbitals.
• Molecular Orbitals: Formed when atomic orbitals overlap, representing electrons on the whole molecule.

Atomic and Molecular Orbitals

• CH4 Example: Carbon is sp3 hybridized bonding with hydrogen's s orbitals.
• H2 Molecule: Two hydrogen atoms form molecular orbitals from atomic orbitals.
  • Linear Combination of Atomic Orbitals (LCAO): Mathematical concept to explain molecular orbitals.
  • Constructive Interference: Low-energy bonding molecular orbital.
  • Destructive Interference: High-energy antibonding molecular orbital (noted with an asterisk, e.g., sigma*).*

Energy Diagrams

• Bonding Orbital: Low energy, more stable state.
• Antibonding Orbital: Higher energy, less stable state, electrons can temporarily occupy this when excited.

Conceptual Analogy

• Electrons likened to relationship dynamics:
  • Bonding: Happy, low-energy, stable relationship.
  • Antibonding: High-energy, unstable, akin to a fight.
• Node: Represents separation in antibonding state.

Pi Bonds and Molecular Orbitals

• Pi Bonds: Second bond in a double bond.
  • Example: Ethene (C2H4) with one sigma and one pi bond.
• Formation: Pi bond forms from non-hybridized p orbitals above and below the molecular plane.
• Energy diagram mirrors that of molecular orbitals for hydrogen.

Visualizing Pi Bonds

• Electrons can move in the pi bond, forming a node in the antibonding state.
• Resonance Structures: Illustrate electron movement in molecular orbitals.

HOMO and LUMO

• Highest Occupied Molecular Orbital (HOMO)
• Lowest Unoccupied Molecular Orbital (LUMO)
  • Will be discussed in further detail in the next video.

Conclusion

• Simplified view of molecular orbital theory is aimed to aid understanding without mathematical complexity.
• Encouraged to view more resources for deeper learning.

Additional Resources

• Video and detailed explanations available at leah4sci.com/m-o theory.