Molecular Orbital Theory Notes

7.6 Summary 1. 7.6 Molecular Orbital Theory a. Intro i. Molecular orbital theory states that the atomic orbitals involved in bonding actually combine to form new orbitals that are the property of the entire molecule, rather than of the individual atoms forming the bonds. 1. The new orbitals are called molecular orbitals. ii. Electrons shared by atoms in a molecule reside in the molecular orbitals. iii. Molecular orbitals are like atomic orbitals in that they have specific shapes and specific energies and they can each accommodate a maximum of two electrons. iv. Two electrons residing in the same molecular orbital must have opposite spins. v. The number of molecular orbitals we get is equal to the number of atomic orbitals we combine. b. Bonding and Antibonding Molecular Orbitals vi. H2 is the simplest homonuclear diatomic molecule. 2. By valence bond theory, H2 forms by two H atoms’ 1s atomic orbital to overlap. By molecular orbital theory, H2 forms by two H atoms’ 1s atomic orbitals combine to give molecular orbitals. vii. The constructive combination of the two 1s orbitals forms the molecular orbital that lies along the internuclear axis directly between the two H nuclei. 3. Electron density in a molecular orbital that lies between two nuclei will draw them together. This molecular orbital is called a bonding molecular orbital. viii. The destructive combination of the 1s atomic orbitals forms a molecular orbital that lies along the internuclear axis but does not lie between the two nuclei and consists of two lobes. 4. Electron density would pull the two nuclei in opposite directions and is called antibonding molecular orbital. c. σ Molecular Orbitals ix. Molecular orbitals that lie along the internuclear axis are called σ molecular orbitals. x. Bonding molecular orbitals