Worksheet: Molecular Orbital Theory

In this worksheet, we will practice describing the shapes, energies and electron occupancies of bonding, nonbonding, and antibonding molecular orbitals.

Q1:

An sp2 hybridized atom in a molecule forms šœŽ 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 dipole moment of each bond is zero.
  • BThe three bonds contribute equally to each bonding molecular orbital.
  • CAll of the bonds are partial double bonds.
  • DThe three bonds contribute equally to each bonding energy level.
  • EThe molecular bonding orbitals have the same energy.

Q2:

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

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

Q3:

Which of the following statements is false?

  • AWhen atomic orbitals overlap to form molecular orbitals, the total number of orbitals does not change.
  • BThe greatest overlap between an atomic orbital and a šœ‹ antibonding orbital is produced when the atomic orbital approaches the šœ‹ bond axis at 90āˆ˜.
  • CThe greatest overlap between an atomic orbital and a šœŽ antibonding orbital is produced when the atomic orbital approaches parallel to the šœŽ bond axis.
  • DWhen two p orbitals overlap to form a šœŽ bond, most of the electron density is concentrated between the nuclei.
  • EMolecules containing an even number of electrons can be paramagnetic.

Q4:

Which of the following statements is true?

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

Q5:

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

  • ABonds formed by p orbitals are always weaker than those formed by hybrid sp or sp2 orbitals.
  • BOrbital overlap in a CCšœŽ bond is greater than that in a CCšœ‹ bond.
  • CThe triple bond is weakened by s-p mixing.
  • DRepulsion between the three pairs of bonding electrons reduces the energy of the triple bond.
  • EThe triple bond is weakened by electrons occupying an antibonding orbital.

Q6:

Which of the following electronic transitions do alkanes exhibit?

  • A šœ‹ to šœ‹āˆ—
  • B šœ‹ to šœ‹āˆ—
  • C šœŽ to šœŽāˆ—
  • D šœ‹ to šœŽāˆ—

Q7:

Liquid oxygen is attracted by a magnetic field. Which feature of the O2 molecule is responsible for this behavior?

  • AUnpaired electrons in antibonding orbitals
  • BPaired electrons in antibonding orbitals
  • CPaired electrons in nonbonding orbitals
  • DUnpaired electrons in nonbonding orbitals
  • EUnpaired electrons in bonding orbitals

Q8:

What is the ground-state valence molecular orbital configuration for H2ā€“?

  • A ( šœŽ ) ( šœŽ ) ļŠ§ ļ ļŠØ āˆ— ļŠ§ ļ ļŠ§
  • B ( šœŽ ) ( šœŽ ) ļŠ§ ļ ļŠ§ āˆ— ļŠ§ ļ ļŠ§
  • C ( šœŽ ) ( šœŽ ) ļŠ§ ļ ļŠØ āˆ— ļŠ§ ļ ļŠØ
  • D ( šœŽ ) ( šœŽ ) ļŠ§ ļ ļŠ§ āˆ— ļŠ§ ļ ļŠØ
  • E ( šœŽ ) ( šœŽ ) ļŠ§ ļ ļŠ§ āˆ— ļŠ§ ļ ļŠ¦

Q9:

The molecule Ne2 does not exist in nature.

To 1 decimal place, what is the bond order of Ne2?

From which molecular orbital is an electron removed in the first ionization of Ne2?

  • A šœ‹ ļŠØ ļŒ
  • B šœŽ āˆ— ļŠØ ļŒ
  • C šœ‹ āˆ— ļŠØ ļŒ
  • D šœŽ ļŠØ ļŒ
  • E šœŽ ļŠØ ļ

To 1 decimal place, what is the bond order of Ne2+?

Q10:

What is the valence molecular orbital configuration for F2ā€“?

  • A ( šœŽ ) ( šœŽ ) ļ€ŗ šœŽ ļ† ļ€» šœ‹ , šœ‹ ļ‡ ļ€» šœ‹ , šœ‹ ļ‡ ļ€ŗ šœŽ ļ† ļŠØ ļŠØ āˆ— ļŠØ ļŠØ ļŠØ ļŠØ ļŠØ ļŠØ ļŠŖ āˆ— ļŠØ āˆ— ļŠØ ļŠŖ āˆ— ļŠØ ļŠ§ s s p p p p p p x y z y z x
  • B ( šœŽ ) ( šœŽ ) ļ€» šœ‹ , šœ‹ ļ‡ ļ€ŗ šœŽ ļ† ļ€ŗ šœŽ ļ† ļ€» šœ‹ , šœ‹ ļ‡ ļŠØ ļŠØ āˆ— ļŠØ ļŠØ ļŠØ ļŠØ ļŠŖ ļŠØ ļŠØ āˆ— ļŠØ ļŠØ āˆ— ļŠØ āˆ— ļŠØ ļŠ© s s p p p p p p y z x x y z
  • C ( šœŽ ) ( šœŽ ) ļ€» šœ‹ , šœ‹ ļ‡ ļ€» šœ‹ , šœ‹ ļ‡ ļ€ŗ šœŽ ļ† ļ€ŗ šœŽ ļ† ļŠØ ļŠØ āˆ— ļŠØ ļŠØ ļŠØ ļŠØ ļŠŖ āˆ— ļŠØ āˆ— ļŠØ ļŠØ ļŠØ ļŠØ āˆ— ļŠØ ļŠ§ s s p p p p p p y z y z x x
  • D ( šœŽ ) ( šœŽ ) ļ€» šœ‹ , šœ‹ ļ‡ ļ€ŗ šœŽ ļ† ļ€» šœ‹ , šœ‹ ļ‡ ļ€ŗ šœŽ ļ† ļŠØ ļŠØ āˆ— ļŠØ ļŠØ ļŠØ ļŠØ ļŠŖ ļŠØ ļŠØ āˆ— ļŠØ āˆ— ļŠØ ļŠŖ āˆ— ļŠØ ļŠ§ s s p p p p p p y z x y z x
  • E ( šœŽ ) ( šœŽ ) ļ€ŗ šœŽ ļ† ļ€» šœ‹ , šœ‹ ļ‡ ļ€ŗ šœŽ ļ† ļ€» šœ‹ , šœ‹ ļ‡ ļŠØ ļŠØ āˆ— ļŠØ ļŠØ ļŠØ ļŠØ ļŠØ ļŠØ ļŠŖ āˆ— ļŠØ ļŠØ āˆ— ļŠØ āˆ— ļŠØ ļŠ© s s p p p p p p x y z x y z

Q11:

What is the valence molecular orbital configuration for N2+?

  • A ( šœŽ ) ( šœŽ ) ļ€ŗ šœŽ ļ† ļ€» šœ‹ , šœ‹ ļ‡ ļ€» šœ‹ , šœ‹ ļ‡ ļŠØ ļŠØ āˆ— ļŠØ ļŠØ ļŠØ ļŠØ ļŠØ ļŠØ ļŠŖ āˆ— ļŠØ āˆ— ļŠØ ļŠ§ s s p p p p p x y z y z
  • B ( šœŽ ) ( šœŽ ) ļ€» šœ‹ , šœ‹ ļ‡ ļ€ŗ šœŽ ļ† ļ€» šœ‹ , šœ‹ ļ‡ ļŠØ ļŠØ āˆ— ļŠØ ļŠØ ļŠØ ļŠØ ļŠŖ ļŠØ ļŠØ āˆ— ļŠØ āˆ— ļŠØ ļŠ¦ s s p p p p p y z x y z
  • C ( šœŽ ) ( šœŽ ) ļ€» šœ‹ , šœ‹ ļ‡ ļ€» šœ‹ , šœ‹ ļ‡ ļ€ŗ šœŽ ļ† ļŠØ ļŠØ āˆ— ļŠØ ļŠØ ļŠØ ļŠØ ļŠŖ āˆ— ļŠØ āˆ— ļŠØ ļŠØ ļŠØ ļŠ¦ s s p p p p p y z y z x
  • D ( šœŽ ) ( šœŽ ) ļ€» šœ‹ , šœ‹ ļ‡ ļ€ŗ šœŽ ļ† ļ€» šœ‹ , šœ‹ ļ‡ ļŠØ ļŠØ āˆ— ļŠØ ļŠØ ļŠØ ļŠØ ļŠŖ ļŠØ ļŠ§ āˆ— ļŠØ āˆ— ļŠØ ļŠ¦ s s p p p p p y z x y z
  • E ( šœŽ ) ( šœŽ ) ļ€ŗ šœŽ ļ† ļ€» šœ‹ , šœ‹ ļ‡ ļ€» šœ‹ , šœ‹ ļ‡ ļŠØ ļŠØ āˆ— ļŠØ ļŠØ ļŠØ ļŠØ ļŠØ ļŠØ ļŠ© āˆ— ļŠØ āˆ— ļŠØ ļŠ¦ s s p p p p p x y z y z

Q12:

Which of the following ions has the valence molecular orbital configuration: (šœŽ)(šœŽ)ļ€ŗšœ‹,šœ‹ļ†ļ€¹šœŽļ…ļ€ŗšœ‹,šœ‹ļ†ļ€ŗšœŽļ†ļŠØļļŠØāˆ—ļŠØļļŠØļŠØļŒļŠØļŒļŠŖļŠØļŒļŠØāˆ—ļŠØļŒāˆ—ļŠØļŒļŠ§āˆ—ļŠØļŒļŠ¦ļ‘‘ļ‘’ļ‘ļ‘‘ļ‘’ļ‘?

  • A N 2 ā€“
  • B O 2 +
  • C O 2 2 +
  • D C 2 2 ā€“
  • E F 2 2 +

Q13:

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

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

Q14:

Which orbital would you expect to be the LUMO for a peroxide ion, O22ā€“?

  • A šœŽ āˆ— ļŠØ p
  • B šœ‹ ļŠØ p
  • C šœ‹ āˆ— ļŠØ p
  • D šœŽ ļŠØ p

Q15:

Which of the following statements is true about nonbonding molecular orbitals?

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

Q16:

According to valence bond theory (VBT), O2 has no unpaired electrons. MO theory shows two unpaired electrons in a 2nāˆ— molecular orbital. Which of the following experiments supports the correct electron configuration?

  • AThere is no way to know which theory is correct.
  • BAn EPR spectrum shows that oxygen is paramagnetic; VBT is correct.
  • CAn EPR spectrum shows that oxygen is paramagnetic; MO theory is correct.
  • DInfrared spectroscopy shows a double-bond stretch; VBT is correct.
  • EInfrared spectroscopy shows a double-bond stretch; MO theory is correct.

Q17:

For potassium metal, the 4p band represents the and the .

  • ALUMO, bonding orbital
  • BHOMO, nonbonding orbital
  • CHOMO, antibonding orbital
  • DLUMO, antibonding orbital
  • EHOMO, bonding orbital

Q18:

4sā€“4p band overlap allows calcium to behave as a conductor. How many energy levels are present in the conduction band?

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