Atomic orbitals combine into delocalized molecular orbitals spanning the whole molecule.
Practise Bonding & Molecular Structure All Bonding & Molecular Structure topics
Molecular orbital theory combines atomic orbitals into molecular orbitals that extend over the whole molecule. The number of molecular orbitals produced always equals the number of atomic orbitals combined, half bonding and half antibonding in simple cases. Electrons fill the molecular orbitals in order of increasing energy, following the Aufbau and Pauli principles, with Hund's rule for degenerate orbitals. The theory explains properties that valence bond theory cannot, including the paramagnetism of molecular oxygen and bond orders in species with odd numbers of electrons. It is the framework used in modern computational chemistry.
Key ideas: Basic rules: N atomic orbitals give N molecular orbitals, fill from lowest energy, pair spins only when forced, and calculate bond order from the electron count. Overlap needs similar energy and the same symmetry. Orbitals combine as sums and differences. In H2 the bonding MO is lower by an amount beta and the antibonding is higher by a bit more.
Common mistakes and connections: Frequent mistakes are making the antibonding orbital the same distance above as the bonding is below (it is slightly higher), and mixing atomic orbitals of very different energy. Do not assign electrons to specific atoms: they belong to the whole molecule. Links to bond order, magnetism, band theory and delocalization in benzene.
Two atomic orbitals combine into two molecular orbitals, one lower and one higher in energy than the originals, as in the H2 molecule. The interactive lesson shows this as a live animation or chart.
MO theory correctly predicts that O2 is paramagnetic with two unpaired electrons.
Atomic orbitals combine into delocalized molecular orbitals spanning the whole molecule.
Molecular Orbital Theory is a advanced topic in Bonding & Molecular Structure. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in Bonding & Molecular Structure first: sp Hybridization, sp3d and sp3d2 Hybridization, Hybridization of Water and Ammonia.
The next topics in Bonding & Molecular Structure are Bonding Molecular Orbital and Antibonding Molecular Orbital.
Yes. The interactive lesson includes a self-check question on Molecular Orbital Theory, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Molecular Orbital Theory is topic 59 of 104 in Bonding & Molecular Structure.