Molecular Orbital Theory and Hybridization

Content Mastery Review

• Sigma Bonds: Determine the number of sigma bonds in the molecule. Options:

  1. 5
  2. 11
  3. 13
  4. 15

• Pi Bonds: Determine the number of pi bonds. Options:

  1. 2
  2. 5
  3. 13
  4. 15

Hybridization

• Hybridization of Labeled Atoms: Understanding the hybridization of atoms in a molecule is crucial for predicting molecular geometry and bonding properties.

Example: Hybridization of Carbon in HC=C=CH

• Challenge: What is the hybridization of the middle carbon atom in the molecule structure HC=C=CH?

Hybridization Types

sp3d Hybridization

• Geometry: Trigonal bipyramidal
• Requirement: Needs 5 valence shell orbitals to achieve this shape.

sp3d2 Hybridization

• Geometry: Octahedral
• Requirement: Needs 6 valence shell orbitals
  • Diagram appears as:
    • (a)
    • (b)

Determining Hybrid Orbitals of Central Atom

1. Lewis Structure: Draw the Lewis structure of the molecule.
2. Electron Density Regions: Count the number of electron density regions around the central atom.
3. Assign Hybridization: Match the number of regions to the appropriate hybridization type (this is often after observation of the molecule).

Multiple Bonds

• Double Bonds: Treat as trigonal planar.
• Triple Bonds: Represented as linear and extends beyond the connected atoms.

Molecular Orbital Theory

• Definitions:

  • Paramagnetism: Attraction to a magnetic field due to the presence of unpaired electrons.
  • Diamagnetic: All electrons are paired and show weak repulsion from a magnetic field.
  • Note: Not a permanent magnet.

• Concept: The theory involves combining atomic orbitals to form molecular orbitals (MOs) that are delocalized across the entire molecule.

Constructive & Destructive Interference

• A key concept in the formation of molecular orbitals involving overlapping atomic orbitals:
  • Constructive: Leads to bonding orbitals.
  • Destructive: Leads to antibonding orbitals.

Homonuclear Diatomic Molecules

• Atomic Orbitals: Combine through addition to form bonding orbitals and through subtraction to form antibonding orbitals (e.g., $σ^{*}$).

P-Orbital Bonds

• Sigma Bond: Formed via the overlap of p-orbitals (additively).
• Pi Bond: Formed from the side-to-side overlap of p-orbitals.

Drawing Molecular Orbital Diagrams

• Illustrate the combination of atomic orbitals and the resultant molecular orbitals.

Recap

• Key Points:
  • Hybrid orbital assignments (sp3, sp2, sp)
  • MO diagram: Fill with electrons and observe para or diamagnetism.