Molecular Orbital Worksheet



Molecular Orbital Worksheet Key

1. Draw appropriate MO diagrams for the diatomic molecules Si2 and SO+. For each,

determine the bond order and whether the molecule is paramagnetic or diamagnetic.

Si2

AO MO AO

3p(* ______

3p(* ______ ______

3p _(__ _(__ ____ _(__ _(__ ___ 3p

3p( _______

3p( ___((___ ___((____

3s(*___((___

3s ___((__ ___((___ 3s

3s( ___((____

Bond order = ½ (6-2)= 2

All the electrons are paired, the molecule is diamagnetic

SO+.

AO MO AO

3p(* ______

3p(* ___(___ ______

2p _((__ _(__ __(__ _(__ _(__ _(__ 3p

3p( ___((___ ___((____

3p( ___((____

3s(*___((___

2s ___((__ ___((___ 3s

3s( ___((____

Bond order = ½ (8-4)= 2

Not all the electrons are paired, the molecule is paramagnetic

2. Draw the four π-molecular orbitals for the molecule butadiene, drawn below. Label

the four orbitals as bonding, non-bonding or antibonding. Which of the four orbitals

are occupied? Which is the LUMO and which is the HOMO?

[pic]

3. Draw the six π-molecular orbitals for benzene, label them as bonding non-bonding or

antibonding. Which are occupied?

MO Rules for Benzene

➢ Six overlapping p orbitals must form six molecular orbitals

➢ Three will be bonding, three antibonding

➢ Lowest energy MO will have all bonding interactions, no nodes

➢ As energy of MO increases, the number of nodes increases

➢ System symmetric so 2 pairs of degenerate orbitals

[pic]

6 atomic orbitals - 6 molecular orbitals

System symmetric so 2 pairs of degenerate orbitals

[pic]

➢ The six electrons fill three bonding pi orbitals.

➢ All bonding orbitals are filled (“closed shell”), an extremely stable arrangement (AROMATIC STABILIZATION).

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