Molecular orbitals - Practice exercise for exam PDF

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Practice exercise for exam...

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Molecular Orbital Diagrams σ and π orbitals • •

When electrons occupy a bonding orbital, they strengthen the bond. When electrons occupy an anti-bonding orbital, they weaken the bond. Anti-bonding orbitals have a nodal plane between the nuclei: they are zero along the vertical dotted line shown. σ orbitals are symmetric around a line joining the two nuclei. π orbitals have a node along this line: they are zero along the horizontal dotted line shown below.

σ

σ

π

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Molecular orbital diagrams show the energies of molecular orbitals. They are filled with the valence electrons by following the principles: o Fill from the lowest to the highest levels. o Two electrons can occupy each level. o Electrons keep apart by occupying separate levels before pairing up.

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The bond order can be worked out by first counting up the number of bonding and anti-bonding electrons and then calculating: bond order = ½ (number of bonding electrons - number of anti-bonding electrons)...