Energy ordering of molecular orbitals used to derive bond order and magnetism of molecules like N2 and O2.
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A molecular orbital diagram places the atomic orbitals of two identical atoms on the sides and the molecular orbitals in the middle, ordered by energy. For lithium through nitrogen the usual order is sigma 2s, sigma* 2s, pi 2p, sigma 2p, pi* 2p and sigma* 2p, while for oxygen and fluorine the sigma 2p orbital lies below the pi 2p pair. Electrons are filled into these orbitals, and bond order equals half the difference between bonding and antibonding electrons. Unpaired electrons in the final diagram also predict the magnetism of the molecule.
Key ideas: Steps: sum valence electrons, fill in the correct order, compute bond order, find unpaired electrons. Order for B2 through N2 has pi 2p below sigma 2p because of s-p mixing; for O2 and F2 it is reversed. Examples: B2 has two unpaired electrons and is paramagnetic, C2 has bond order 2 and is diamagnetic with both electron pairs in pi bonds, N2 has bond order 3.
Common mistakes and connections: Students use the wrong order for N2 or the wrong one for O2, which gives an incorrect prediction of magnetism: with the O2 order N2 would look paramagnetic. Another error is counting core electrons. Links to s-p mixing, magnetism, spectroscopy and ion stability: N2+ and O2+ comparisons.
O2 ordering of molecular orbitals: 12 valence electrons fill up through the pi* levels, giving bond order 2 with two unpaired electrons. The interactive lesson shows this as a live animation or chart.
N2 has bond order 3, O2 has bond order 2, F2 has bond order 1 and Ne2 has bond order 0.
Energy ordering of molecular orbitals used to derive bond order and magnetism of molecules like N2 and O2.
MO Diagram of Homonuclear Diatomics 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: Molecular Orbital Theory, Bonding Molecular Orbital, Antibonding Molecular Orbital.
The next topics in Bonding & Molecular Structure are Paramagnetism of Oxygen and Diamagnetism.
Yes. The interactive lesson includes a self-check question on MO Diagram of Homonuclear Diatomics, and the Bonding & Molecular Structure quiz draws on every topic in this area.
MO Diagram of Homonuclear Diatomics is topic 62 of 104 in Bonding & Molecular Structure.