Molecular Orbitals

Atomic Orbitals and Hybridization

• Atoms can hybridize atomic orbitals into molecular orbitals
  • Hybridized orbitals resemble combinations of atomic orbitals
  • Used to make covalent bonds (overlapping of orbitals)

Hydrogen Molecule (H2)

• Each hydrogen has 1 electron in a 1s orbital
• To form a sigma bond, these orbitals overlap to form 1 molecular orbital
• Molecular orbital has lower energy than individual hydrogen atoms due to electrostatic interactions
• Formation of H2:
  • 2 atomic orbitals -> 1 bonding orbital + 1 antibonding orbital (orbitals must be conserved)
  • Electrons in covalent bond occupy the lower energy bonding orbital
  • Electrons can jump to antibonding orbital (excitation)

Hybridization in Multiple Bonds

• Atoms use hybrid orbitals to form multiple bonds
• Example: Carbon makes 4 bonds using sp3 hybridized orbitals
  • Carbon promotes a 2s electron to a 2p orbital
  • Hybridizes 2s and all 2p orbitals -> 4 degenerate sp3 orbitals
  • Each sp3 orbital has 1 electron, can form 4 sigma bonds

Types of Hybridization

• sp3 Hybridization: Participates in 4 sigma bonds
• sp2 Hybridization: Participates in 3 sigma bonds + double bond (1 p orbital unhybridized forming pi bond)
  • Example: Double-bonded carbons
• sp Hybridization: Participates in 2 sigma bonds + triple bond (2 p orbitals unhybridized forming two pi bonds)
  • Example: Triple-bonded carbons

Orbital Diagrams and Bond Order

• Diagrams show atomic orbitals and molecular orbitals
• Example: H2
  • 1s orbitals -> fill bonding orbital -> H2 molecule
  • Bond order = (number of bonding electrons - number of antibonding electrons) / 2
  • H2 bond order = 1 (single bond)
• Example: O2
  • Electron configuration and molecular orbitals (1s, 2s, 2p orbitals)
  • Bond order = (10 bonding electrons - 6 antibonding electrons)/2 = 2 (double bond)
• Example: N2
  • Bond order = 3 (triple bond)