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9: Orbital Hybridization and Molecular Orbitals

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    Molecular Orbital and Valence Bond Theory

    Exercise \(\PageIndex{1}\)

    Which of the following statements concerning molecular orbital (MO) bond theory is/are INCORRECT?

    1. MO theory can describe molecular bonding in excited states.
    2. Molecular orbitals are obtained from the combination of atomic orbitals.
    3. MO theory predicts that electrons are delocalized over the molecule through molecular orbitals.

    a. 1 only        b. 2 only        c. 3 only        d. none        e. 1, 2, and 3

    Answer

    d. none

    Exercise \(\PageIndex{2}\)

    Which of the following statements concerning valence bond (VB) theory is/are INCORRECT?

    1. VB theory can describe molecular bonding in excited states.
    2. VB theory assumes that electrons are localized between pairs of atoms.
    3. VB theory predicts localized lone pairs of electrons.

    a. 1 only        b. 2 only        c. 3 only        d. 2 and 3        e. 1, 2, and 3

    Answer

    a. 1 only

    Exercise \(\PageIndex{3}\)

    Which theory, valence bond or molecule orbital, correctly predicts the existence of paramagnetic molecules?

    Answer

    Molecular orbital theory

     

    Sigma (σ) and Pi (π) bonds in Valence Bond Theory (VBT)

    Exercise \(\PageIndex{1}\)

    Which of the following statements concerning hybrid orbitals is/are CORRECT?

    1. The number of hybrid orbitals equals the number of atomic orbitals that are used to create the hybrids.
    2. When atomic orbitals are hybridized, the s orbital and at least one p orbital are always hybridized.
    3. To create tetrahedral structures, the s orbital and all three p orbitals must be hybridized.

    a. 1 only        b. 2 only        c. 3 only        d. 2 and 3        e. 1, 2, and 3

    Answer

    e. 1, 2, and 3

    Exercise \(\PageIndex{2}\)

    Which of the following statements concerning σ and π bonds is/are correct?

    1. Sigma bonds can only be formed from unhybridized orbitals.
    2. Pi bonds are formed from unhybridized p orbitals.
    3. A pi bond has an electron distribution above and below the bond axis.

    a. 1 only        b. 2 only        c. 3 only        d. 1 and 2        e. 2 and 3

    Answer

    e. 2 and 3

    Exercise \(\PageIndex{3}\)

    Which of the following concerning σ and π bonds is/are correct?

    1. A sigma bond may be formed from the sideways overlap of two parallel p orbitals.
    2. No more than two pi bonds are possible between adjacent carbon atoms.
    3. The considerable energy required to rotate pi bonded atoms is the primary reason for geometrical isomerism in some pi bonded molecules.

    a. 1 only        b. 2 only        c. 3 only        d. 1 and 2        e. 2 and 3

    Answer

    e. 2 and 3

     

    Number of Sigma (σ) and Pi (π) bonds 

    Exercise \(\PageIndex{4}\)

    How many sigma and pi bonds are in the molecule pictured below?

    Answer

    thirteen sigma bonds and one pi bond

    Exercise \(\PageIndex{5}\)

    How many sigma (σ) bonds and pi (π) bonds are in dioxygen?

    Answer

     one σ, two π

    Exercise \(\PageIndex{6}\)

    How many sigma (σ) bonds and pi (π) bonds are present in the given molecule?

    9.2.2.png

    Answer

    Seven σ and three π

     

    Hybridization 

    Exercise \(\PageIndex{7}\)

    What is the hybridization of the central nitrogen atom in N2O?

    Answer

    sp

    Exercise \(\PageIndex{8}\)

    What is the hybridization of the sulfur atom in SCl2?

    Answer

    sp3

    Exercise \(\PageIndex{9}\)

    The hybridization of the nitrogen atom in NH3 is _____.   

    Answer

    sp3

    Exercise \(\PageIndex{10}\)

    In valence bond theory, each sigma bond in CH4 is formed from the overlap of a hydrogen atom's 1s orbital with a(n) ________ hybridized orbital on the carbon atom.

    Answer

    sp3

    Exercise \(\PageIndex{11}\)

    SF3+, has a tetrahedral electron-pair geometry and a trigonal-pyramidal molecular geometry. The hybridization of the central sulfur atom is ________.

    Answer

    sp

    Exercise \(\PageIndex{12}\)

    The hybridization of the carbon atom in CF3+ is ________.

    Answer

    sp2

     

    Hybridization and Molecular Geometry 

    Exercise \(\PageIndex{13}\)

    In the context of valence shell electron pair repulsion (VSEPR) theory, what is the molecular geometry around a central atom that is sp3 hybridized and has one lone pair of electrons?

    Answer

    trigonal-pyramidal

    Exercise \(\PageIndex{14}\)

    What is the molecular geometry around a central atom that is sp2 hybridized, has three sigma bonds, and one pi bond?

    Answer

    trigonal-planar

    Exercise \(\PageIndex{15}\)

    When an atom in a molecule or ion is described as sp3 hybridized, its electron pair geometry is

    Answer

    tetrahedral

     

    Reactions and Hybridization 

    Exercise \(\PageIndex{16}\)

    Upon combustion, ethene (C2H4) is converted to carbon dioxide and water.What change occurs in the hybridization of carbon atoms in this reaction?

    Answer

    sp2 to sp

    Exercise \(\PageIndex{17}\)

    Ammonia reacts with oxygen and water to produce nitric acid. What change in hybridization of the nitrogen atom occurs in this reaction?

    Answer

    sp3 to sp2

    Exercise \(\PageIndex{18}\)

    Nitric acid, HNO3, dissociates in water to form nitrate ions and hydronium ions. What change in hybridization of the nitrogen atom occurs in this dissociation?

    Answer

    no change

     

    Label Hybridization from Lewis Dot Structures 

    Exercise \(\PageIndex{19}\)

    Which of the underlined atoms (C1, C2, N, and O) are sp2 hybridized?

    9.2.4.png

    Answer

    C1 and  C2

    Exercise \(\PageIndex{20}\)

    Which of the labeled carbon atoms (C1-C4) is/are sp hybridized?

    9.2.5.png

    Answer

    C3

    Exercise \(\PageIndex{21}\)

    What is the hybridization of oxygen atom O?

    9.2.6.png

    Answer

    sp2

     

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

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