Chemistry 1027A/B Chapter Notes - Chapter 2.4: Molecular Orbital Diagram, Molecular Orbital Theory, Antibonding Molecular Orbital
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Major deficiencies in vb: the assumption that electrons are localized is not entirely correct. For example, in resonance hybrids the electrons are delocalized. It does not provide obvious insight on the relative energies of the electrons. It fails to explain certain phenomena, such as whether molecules are paramagnetic or diamagnetic. Molecular orbital (mo) theory takes a delocalized approach to bonding and focuses on the wave behaviour of electrons. In mo, molecular orbitals are formed by combining wave functions of atomic orbitals. This can occur in two ways: constructively and destructively. Constructive combination occurs when two atomic orbitals in the same phase (either both + or both -) combine and form a bonding mo, but it doesn"t generate any new nodes between the nuclei. The combination increases the electron density between the two nuclei, consistent with the formation of a bond. The resulting mo is termed bonding and designated 1s.