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Lesson: Molecular Orbital Theory

In this lesson, we will learn how to describe the shapes, energies and electron occupancies of bonding, nonbonding, and antibonding molecular orbitals.

Worksheet • 15 Questions

Q1:

What is the ground-state valence molecular orbital configuration for H 2 – ?

  • A ( 𝜎 ) ( 𝜎 )    βˆ—   
  • B ( 𝜎 ) ( 𝜎 )    βˆ—   
  • C ( 𝜎 ) ( 𝜎 )    βˆ—   
  • D ( 𝜎 ) ( 𝜎 )    βˆ—   
  • E ( 𝜎 ) ( 𝜎 )    βˆ—   

Q2:

Which of the following statements is true?

  • AMolecules containing an odd number of electrons are always paramagnetic.
  • BIf a molecule contains multiple bonds, the highest-energy occupied orbitals are always πœ‹ bonding orbitals.
  • COnly two atoms can contribute to a bonding orbital.
  • DIn the lowest-energy state of a stable molecule, electrons never occupy an antibonding orbital.
  • EIn the lowest-energy state of a stable molecule, electrons in bonding orbitals are always paired.

Q3:

The molecule N e 2 does not exist in nature.

To 1 decimal place, what is the bond order of N e 2 ?

From which molecular orbital is an electron removed in the first ionization of N e 2 ?

  • A 𝜎 βˆ— 2 𝑝
  • B πœ‹ 2 𝑝
  • C 𝜎 2 𝑝
  • D πœ‹ βˆ— 2 𝑝
  • E 𝜎 2 𝑠

To 1 decimal place, what is the bond order of N e 2 + ?

Q4:

An sp2 hybridized atom in a molecule forms 𝜎 bonds to three other atoms of the same element. There are no other bonds in the molecule. Which of the following statements is true?

  • AThe three bonds contribute equally to each bonding energy level.
  • BAll of the bonds are partial double bonds.
  • CThe dipole moment of each bond is zero.
  • DThe three bonds contribute equally to each bonding molecular orbital.
  • EThe molecular bonding orbitals have the same energy.

Q5:

What is the valence molecular orbital configuration for F 2 – ?

  • A ( 𝜎 ) ( 𝜎 ) ο€Ί 𝜎  ο€» πœ‹ , πœ‹  ο€» πœ‹ , πœ‹  ο€Ί 𝜎  2 2 βˆ— 2 2 2 2 2 2 4 βˆ— 2 βˆ— 2 4 βˆ— 2 1 s s p p p p p p x y z y z x
  • B ( 𝜎 ) ( 𝜎 ) ο€» πœ‹ , πœ‹  ο€» πœ‹ , πœ‹  ο€Ί 𝜎  ο€Ί 𝜎  2 2 βˆ— 2 2 2 2 4 βˆ— 2 βˆ— 2 2 2 2 βˆ— 2 1 s s p p p p p p y z y z x x
  • C ( 𝜎 ) ( 𝜎 ) ο€Ί 𝜎  ο€» πœ‹ , πœ‹  ο€Ί 𝜎  ο€» πœ‹ , πœ‹  2 2 βˆ— 2 2 2 2 2 2 4 βˆ— 2 2 βˆ— 2 βˆ— 2 3 s s p p p p p p x y z x y z
  • D ( 𝜎 ) ( 𝜎 ) ο€» πœ‹ , πœ‹  ο€Ί 𝜎  ο€Ί 𝜎  ο€» πœ‹ , πœ‹  2 2 βˆ— 2 2 2 2 4 2 2 βˆ— 2 2 βˆ— 2 βˆ— 2 3 s s p p p p p p y z x x y z
  • E ( 𝜎 ) ( 𝜎 ) ο€» πœ‹ , πœ‹  ο€Ί 𝜎  ο€» πœ‹ , πœ‹  ο€Ί 𝜎  2 2 βˆ— 2 2 2 2 4 2 2 βˆ— 2 βˆ— 2 4 βˆ— 2 1 s s p p p p p p y z x y z x

Q6:

Which of the following statements is true of non-bonding molecular orbitals?

  • AThey are similar in energy to the atomic orbitals.
  • BThey are responsible for the formation of 𝜎 bonds.
  • CThey are responsible for the formation of πœ‹ bonds.
  • DThey help hold the molecule together, once it is formed.
  • EThey counteract bond formation in a molecule.

Q7:

What is the main reason that bonding molecular orbitals are lower in energy than the parent atomic orbitals?

  • AThe electrons in a bonding orbital are attracted to more than one atomic nucleus.
  • BThe electrons in a bonding orbital repel each other more weakly.
  • CBonding orbitals are less symmetrical than atomic orbitals.
  • DThe electrons in a bonding orbital are more weakly shielded by the core electrons of the parent atoms.
  • EThe electrons in a bonding orbital have a lower orbital angular momentum.

Q8:

The average bond energy of a C C single bond is 347 kJ/mol, while that of a C C triple bond is 839 kJ/mol. Why is a triple bond between carbon atoms not three times as strong as a single bond?

  • AOrbital overlap in a C C 𝜎 bond is greater than that in a C C πœ‹ bond.
  • BThe triple bond is weakened by electrons occupying an antibonding orbital.
  • CRepulsion between the three pairs of bonding electrons reduces the energy of the triple bond.
  • DBonds formed by p orbitals are always weaker than those formed by hybrid sp or sp2 orbitals.
  • EThe triple bond is weakened by s-p mixing.

Q9:

Which of the following statements is false?

  • AThe greatest overlap between an atomic orbital and a πœ‹ antibonding orbital is produced when the atomic orbital approaches at 9 0 ∘ to the πœ‹ bond axis.
  • BThe greatest overlap between an atomic orbital and a 𝜎 antibonding orbital is produced when the atomic orbital approaches parallel to the 𝜎 bond axis.
  • CWhen atomic orbitals overlap to form molecular orbitals, the total number of orbitals does not change.
  • DWhen two p orbitals overlap to form a 𝜎 bond, most of the electron density is concentrated between the nuclei.
  • EMolecules containing an even number of electrons can be paramagnetic.

Q10:

Liquid oxygen is attracted by a magnetic field. Which feature of the O 2 molecule is responsible for this behaviour?

  • AUnpaired electrons in antibonding orbitals
  • BPaired electrons in antibonding orbitals
  • CUnpaired electrons in non-bonding orbitals
  • DPaired electrons in non-bonding orbitals
  • EUnpaired electrons in bonding orbitals

Q11:

Alkanes exhibit which of the following electronic transitions?

  • A 𝜎 to 𝜎 βˆ—
  • B πœ‹ to πœ‹ βˆ—
  • C πœ‹ to πœ‹ βˆ—
  • D πœ‹ to 𝜎 βˆ—

Q12:

According to molecular orbital theory, which of the following molecules is the most stable?

  • A N 2
  • B C 2
  • C B e 2
  • D B 2

Q13:

What is the valence molecular orbital configuration for N 2 + ?

  • A ( 𝜎 ) ( 𝜎 ) ο€» πœ‹ , πœ‹  ο€Ί 𝜎  ο€» πœ‹ , πœ‹    βˆ—     οŠͺ   βˆ—  βˆ—   s s p p p p p y z x y z
  • B ( 𝜎 ) ( 𝜎 ) ο€» πœ‹ , πœ‹  ο€» πœ‹ , πœ‹  ο€Ί 𝜎    βˆ—     οŠͺ βˆ—  βˆ—     s s p p p p p y z y z x
  • C ( 𝜎 ) ( 𝜎 ) ο€Ί 𝜎  ο€» πœ‹ , πœ‹  ο€» πœ‹ , πœ‹    βˆ—        βˆ—  βˆ—   s s p p p p p x y z y z
  • D ( 𝜎 ) ( 𝜎 ) ο€» πœ‹ , πœ‹  ο€Ί 𝜎  ο€» πœ‹ , πœ‹    βˆ—     οŠͺ   βˆ—  βˆ—   s s p p p p p y z x y z
  • E ( 𝜎 ) ( 𝜎 ) ο€Ί 𝜎  ο€» πœ‹ , πœ‹  ο€» πœ‹ , πœ‹    βˆ—       οŠͺ βˆ—  βˆ—   s s p p p p p x y z y z

Q14:

Which orbital would you expect to be the LUMO for a O 2 2 – peroxide ion?

  • A 𝜎 βˆ—  p
  • B πœ‹  p
  • C πœ‹ βˆ—  p
  • D 𝜎  p

Q15:

Which of the following ions has the valence molecular orbital configuration: ( 𝜎 ) ( 𝜎 ) ο€Ί πœ‹ , πœ‹  ο€Ή 𝜎  ο€Ί πœ‹ , πœ‹  ο€Ί 𝜎  2 𝑠 2 βˆ— 2 𝑠 2 2 𝑝 2 𝑝 4 2 𝑝 2 βˆ— 2 𝑝 βˆ— 2 𝑝 1 βˆ— 2 𝑝 0 𝑦 𝑧 π‘₯ 𝑦 𝑧 π‘₯ ?

  • A N 2 –
  • B O 2 2 +
  • C O 2 +
  • D C 2 2 –
  • E F 2 2 +
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