structure and bonding: MO theory for O2 and F2

diatomic molecules with p orbitals: Pz

• Pz + Pz - out of phase combination, antibonding sigma orbital as charges cancel so there’s reduced electron density between the 2 atoms

• Pz - Pz - in phase combination, bonding sigma orbital as creates bigger negative charge so there is increased electron density between the 2 atoms

diatomic molecules with p orbitals: Px and Py

• Px + Px - in phase combination, bonding pi orbital as symmetry uncylindrical, 2 areas of wavefunction separated by node in the yz plane

• Px - Px - out of phase combination, antibonding pi orbital, 4 areas of wavefunction separated by 2 nodal planes

• Px and Py degenerate

Zeff

• effective nuclear charge - net positive charge experienced by an electron in a multi-electron atom

triplet and singlet O2

• 2 parallel spins give rise to triplet ground state - lowest energy

• last 2 electrons with parallel spins in same orbital gives singlet state

• 2 possible singlet states - each slightly higher in energy that ground state

• biological processes can produce singlet oxygen - bad as can cause cancer