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9.3: Molecular Orbital Theory

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    Theory

    Exercise \(\PageIndex{1}\)

    All of the following statements concerning molecular orbital (MO) theory are correct EXCEPT

    1. the Pauli exclusion principle is obeyed.
    2. Hund's rule is obeyed.
    3. electrons are assigned to orbitals of successively higher energy.
    4. a bonding molecular orbital is lower in energy than its parent atomic orbitals.
    5. the combination of two atomic orbitals creates only one molecular orbital.
    Answer

    e. the combination of two atomic orbitals creates only one molecular orbital.

    Exercise \(\PageIndex{2}\)

    Atomic orbitals combine most effectively to form molecular orbitals when

    1. electrons in the orbitals have no spins.
    2. electrons in the orbitals have the same spin.
    3. the atoms have an equal number of valence electrons.
    4. the atomic orbitals have similar energies.
    5. only d-orbitals are used in bonding.
    Answer

    d. the atomic orbitals have similar energies.

    Exercise \(\PageIndex{3}\)

    A molecular orbital that decreases the electron density between two nuclei is said to be ____.

    1. hybridized
    2. bonding
    3. antibonding
    4. pi-bonding
    5. nonpolar
    Answer

    c. antibonding

     

    Molecular Orbital Diagram

    The molecular orbital diagram below may be used for the following problem(s). For oxygen and fluorine, the σ2p orbital should be lower in energy than the π2p orbitals. However, the diagram will still yield correct bond order and magnetic behavior for these molecules.

     9.3.1.png

    Diagram \(\PageIndex{1}\): Use for the following problems in this section.

    Exercise \(\PageIndex{4}\)

    Refer to Diagram \(\PageIndex{1}\). According to molecular orbital theory, which of the following species will have the highest bond order?

    a. H2-        b. Li2        c. C2+        d. N2        e. H2

    Answer

    d. N2

    Exercise \(\PageIndex{5}\)

    Refer to Diagram \(\PageIndex{1}\). According to molecular orbital theory, which of the following species will have the lowest bond order?

    a. He2+       b. H2        c. C2+        d. F22+        e. F2

    Answer

    a. He2+ 

    Exercise \(\PageIndex{6}\)

    Refer to Diagram \(\PageIndex{1}\). According to molecular orbital theory, what is the bond order of O2-?

    a. 1        b. 1.5        c. 2        d. 2.5        e. 3

    Answer

    b. 1.5

    Exercise \(\PageIndex{7}\)

    Refer to Diagram \(\PageIndex{1}\). According to molecular orbital theory, which of the following lists ranks the fluorine species (F2, F22+, F22-) in terms of increasing bond order?

    Answer

    F22– < F2 < F22+

    Exercise \(\PageIndex{8}\)

    Refer to Diagram \(\PageIndex{1}\). Consider the molecules B2, C2, N2 and F2. Which two molecules have the same bond order?

    Answer

    B2 and F2

    Exercise \(\PageIndex{9}\)

    Refer to Diagram \(\PageIndex{1}\). According to molecular orbital theory, which of the following species will be diamagnetic?

    a. O2        b. C2+        c. F2-        d. H2        e. Li2+                     

    Answer

    d. H2

    Exercise \(\PageIndex{10}\)

    Refer to Diagram \(\PageIndex{1}\). According to molecular orbital theory, which of the following species will be paramagnetic?

    a. Li2        b. C2        c. C2-        d. F2        e. O22+

    Answer

    c. C2-

    Exercise \(\PageIndex{11}\)

    Refer to Diagram \(\PageIndex{1}\). According to molecular orbital theory, which of the following species will have only one unpaired electron?

    a. C2        b. Ne22+        c. O22-        d. N2        e. O2+

    Answer

    e. O2+

    Exercise \(\PageIndex{12}\)

    Refer to Diagram \(\PageIndex{1}\). Which of the following is the correct molecular orbital configuration of F2?

    1. [core electrons] (σ2s)2 (σ*2s)2 (σ2p)2 (π2p)4 (σ*2p)2
    2. [core electrons] (σ2s)2 (σ*2s)2 (π2p)2 (σ2p)2 (π*2p)2
    3. [core electrons] (σ2s)2 (σ*2s)2 (π2p)4 (π*2p)4
    4. [core electrons] (σ2s)2 (σ*2s)2 (π2p)4 (σ2p)2 (π*2p)6
    5. [core electrons] (σ2s)2 (σ*2s)2 (σ2p)2 (π2p)4 (π*2p)4
    Answer

    e. [core electrons] (σ2s)2 (σ*2s)2 (σ2p)2 (π2p)4 (π*2p)4

    Exercise \(\PageIndex{13}\)

    Refer to Diagram \(\PageIndex{1}\). Assuming that the molecular orbital energy diagram for a homonuclear diatomic molecule applies to a heteronuclear diatomic molecule, determine which of the following species has the highest bond order.

    a. NO-        b. OF-        c. C2        d. O22-        e. NO+

    Answer

    e. NO+

    Exercise \(\PageIndex{14}\)

    Refer to Diagram \(\PageIndex{1}\). Identify the molecule or ion with the longest bond length.

    a. O2        b. O2+        c.O2-        d. O22-        e.O22+

    Answer

    d. O22-

    Exercise \(\PageIndex{15}\)

    Refer to Diagram \(\PageIndex{1}\). Identify the molecule with the shortest bond length.

    a. O2        b. C2        c. B2        d. F2        e. N2

    Answer

    e. N2

     

    Bond Order 

    Exercise \(\PageIndex{16}\)

    The electron configuration of a particular diatomic species is:

    [core electrons](σ2s)2(σ*2s)2(σ2p)2(π2p)3(π*2p)0

    What is the bond order for this species?

    Answer

    2

    Exercise \(\PageIndex{17}\)

    If 7 orbitals on one atom overlap 7 orbitals on a second atom, how many molecular orbitals will be formed?

    Answer

    14

    Exercise \(\PageIndex{18}\)

    What does the following figure represent?

    9.3.2.png

    1. the overlap of two 1s orbitals to form a σ bond
    2. the overlap of two 2p orbitals to form a σ bond
    3. the overlap of two 2p orbitals to form a π bond
    4. the overlap of a 1s orbital and a 2p orbital to form a σ bond
    5. the overlap of a 1s orbital and a 2p orbital to form a π bond
    Answer

    d. the overlap of a 1s orbital and a 2p orbital to form a σ bond

     

    Valence Molecular Orbital Energy Level Diagram 

    Exercise \(\PageIndex{19}\)

    Which of the following molecules has the below valence molecular orbital energy level diagram?

    a. Li2        b. Be2        c. B2        d. C2        e. N2    

    Answer

    e. N2    

    Exercise \(\PageIndex{20}\)

    The following valence molecular orbital energy level diagram is appropriate for which one of the listed species?

    a. B22+        b. C22+        c. N22+        d. O22+        e. F22+

    Answer

    e. F22+

    Exercise \(\PageIndex{21}\)

    Which diatomic molecule or ion has valence electron molecular orbital configuration provided below?

    [core electrons](σ2s)2(σ*2s)2(σ2p)2(π2p)4(π*2p)3

    a. B2        b. O2-        c. O22+        d. Ne2        e. Li2

    Answer

    b. O2- 

    Exercise \(\PageIndex{22}\)

    In the NO2– ion, each atom can be viewed as sp2 hybridized. Thus, each atom has one remaining unhybridized p orbital. How many π2p molecular orbitals (including both bonding and antibonding orbitals) are formed using the unhybridized p orbitals?

    a. 1        b. 3        c. 4        d. 6        e. 12

    Answer

    b. 3

    9.3: Molecular Orbital Theory is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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