CHEM 2303 - Supplementary Problems - Part 2

Linear Combinations of Atomic Orbitals (LCAO's)

Question 1

a. sp3d: Square Pyramidal, axial-base angle = 90°

Coordinate System for Square Pyramidal

LCAO for Square Pyramidal

b. sp3d: Square Pyramidal, axial-base angle = 90°

Coordinate System for Square Pyramidal

LCAO for Square Pyramidal

Question 2

a. sp3d: Trigonal Bipyramidal

Coordinate System for Trigonal Bipyramidal

LCAO for Trigonal Bipyramidal

Homonuclear Diatomic MO Diagrams

Question 1

MO Diagram of B2

B2 Structures

The Lewis Structure predicts either three bonds or one bond and a lone pair of electrons on each boron atom. The MO Diagram predicts two lone pairs of electrons and a lone electron on each boron atom - no bonds. The MO Diagram predicts a paramagentic molecule.


Question 2

MO Diagram of C2

C2 Structures

The Lewis Structure and the MO Diagram both predict two bonds and a lone pair of electrons on each carbon atom, however the Lewis structure predicts one σ and one π bond while the MO Diagram predicts two π bonds. The MO Diagram predicts a diamagnetic molecule.


Question 3

MO Diagram of O2

O2 Structures

The Lewis Structure predicts two bonds and two lone pairs of electrons on each oxygen atom. The MO Diagram predicts one bond, two lone pairs of electrons and a lone electron on each oxygen atom. The MO Diagram predicts a paramagentic molecule.


Heteronuclear Diatomic MO Diagrams

Question 1

MO Diagram of NO+

NO+ Structures

Both the Lewis Structure and the MO Diagram predict three bonds and a lone pair of electrons on each atom. Since the HOMO is a bonding MO (and therefore based primarily on oxygen), NO+ would be expected to coordinate through the oxygen atom. A better representation of this molecule by an MO Diagram would have the 2s orbital on oxygen has non-bonding and the 2s orbital on nitrogen and the 2pz orbital on oxygen forming the σ bond, leaving the 2pz orbital on nitrogen as non-bonding and the HOMO (explaining why the molecule bonds through nitrogen)


Question 2

MO Diagram of NO-

NO- Structures

Similar to O2, the Lewis Structure predicts two bonds and two lone pairs of electrons on each atom while the MO Diagram predicts one bond, two lone pairs of electrons and a lone electron on each atom. Since the HOMO is of π symmetry, the MO Diagrams predicts that NO- would coordinate to a metal complex through a π bond.