Lecture 5

Question 1

Draw the px, py and pz orbitals

Question 2

Draw a diagram to demonstrate the in-phase combination of pz orbitals

Question 3

Draw a diagram to demonstrate the out of phase combination of pz orbitals

Question 4

Draw a diagram to demonstrate the in-phase combination of px orbitals

Question 5

Draw a diagram to demonstrate the out of phase combination of px orbitals

Question 6

Describe the shape of sigma bonds

Answer 6

sigma and sigma* are cylindrically symmetrical along the internuclear axis

Question 7

Describe the shape of pi bonds

Answer 7

• pi and pi* bonds have a nodal plane along the internuclear axis
• Antibonding MOs have more nodes than the corresponding bonding MOs. More nodes, more energy

Question 8

What type of interference occurs between 2 orbitals in the same phase?

Answer 8

constructive

Question 9

What type of interference occurs between 2 orbitals in different phases?

Answer 9

destructive

Question 10

Describe the interaction between orbitals in the same phase

Answer 10

• constructive interference
• the signs of the wavefunctions are the same, so this gives a bonding interaction

Question 11

Describe the interaction between 2 orbitals with different phases

Answer 11

• destructive interference
• the signs of the wavefunctions are opposite so this gives an antibonding interaction

Question 12

Describe the interaction between pz and px/py orbital

Answer 12

• wrong symmetry to interact
• no net interaction between a pz and px (or py) orbital as bonding and antibonding interactions cancel out

Question 13

What does degenerate MOs mean?

Answer 13

they have the same energy

Question 14

What are the MO labels?

Answer 14

g= symmetric with respect to inversion e.g. sigma and pi*
+ to +
u= antisymmetric with respect to inversion e.g. sigma* and pi
+ to -