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9.2: Valence Bond Theory

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    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

    9.2: Valence Bond 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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