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8.E: Chemical Bonding and Molecular Geometry- Homework

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    Turn in your answers for the following questions - show your work

    Draw Lewis dot structures, determine the molecular shape, electronic geometry, bond length, determine the bond energy, determine the bond polarity, and determine the formal charge for each atom.

    1. a. H2
    2. b. CH4
    3. c. NH3
    4. d. H2O
    5. e. HBr
    6. f. PCl5
    7. g. CO2
    8. h. BF3
    9. i. CF2Cl2
    10. j. C4H8 (3 different structures)

     

    The Following Questions are for your practice - Do Not Turn In.  They include answers so you can check your work

    Ionic Bonding

    1. Predict the charge on the monatomic ions formed from the following atoms in binary ionic compounds:
      1. Mg
      2. Al
      3. O
      4. Cl
      answer

      Mg2+; Al3+; O2–; Cl–

    Covalent Bonding

    1. Predict which of the following compounds are ionic and which are covalent, based on the location of their constituent atoms in the periodic table:
      1. Cl2CO
      2. MnO
      3. NCl3
      4. CoBr2
      answer

      ionic: (b), (d); covalent: (a), (c)

    2. From its position in the periodic table, determine which atom in each pair is more electronegative:
      1. Br or Cl
      2. N or O
      answer

      Cl; O

    3. Identify the more polar bond in each of the following pairs of bonds:
      1. HF or HCl
      2. NO or CO
      answer

      HF; CO

    Lewis Symbols and Structures

    1. Write the Lewis symbols for each of the following ions:
      1. As3–
      2. I–
      answer

      eight electrons:

      CNX_Chem_07_03_Question1a_img.jpg

      eight electrons:

      CNX_Chem_07_03_Question1b_img.jpg

    2. Write the Lewis symbols of the ions in each of the following ionic compounds and the Lewis symbols of the atom from which they are formed:
      1. MgS
      2. Al2O3
      answer

      (a)

      Two Lewis structures are shown. The left shows the symbol M g with a superscripted two positive sign while the right shows the symbol S surrounded by eight dots and a superscripted two negative sign. ;

      (b)

      Two Lewis structures are shown. The left shows the symbol A l with a superscripted three positive sign while the right shows the symbol O surrounded by eight dots and a superscripted two negative sign. ;

       

    3. Write Lewis structures for the following:
      1. O2
      2. H2CO
      3. AsF3
      answer

      (a)

      O2 Lewis Dot.jpg

      (b)

      CH2O Lewis Dot.jpg ;

      (c)

      ASF3 Lewis Dot.jpg ;

       

       

    4. Write Lewis structures for the following:
      1. SeF6
      2. XeF4
      3. \(\ce{SeCl3+}\)
      answer

      SeF6:

      SeF6 Lewis Dot.jpg ;

      XeF4:

      XeF4 Lewis Dot.jpg ;

      \(\ce{SeCl3+}\):

      SeCl3 Lewis Dot.jpg

    5. Methanol, H3COH, is used as the fuel in some race cars. Ethanol, C2H5OH, is used extensively as motor fuel in Brazil. Both methanol and ethanol produce CO2 and H2O when they burn. Write the chemical equations for these combustion reactions using Lewis structures instead of chemical formulas.
      answer

      methanol_combustion.jpg

    6. The arrangement of atoms in several biologically important molecules is given here. Complete the Lewis structures of these molecules by adding multiple bonds and lone pairs. Do not add any more atoms.

      the amino acid serine:

      serine_skeleton.jpg

      urea:

      urea_skeleton.jpg

       

      answer

      (a)

      serine Lewis Dot.jpg ;

      (b)

      urea_lewis dot.jpg ;

       

    Formal Charges and Resonance

    1. Draw all possible resonance structures for each of these compounds. Determine the formal charge on each atom in each of the resonance structures:
      1. SO2
      2. \(\ce{NO2-}\)
      answer

      (a)

      SO2 Lewis Dot.jpg ;

      (b)

      NO2 Lewis Dot.jpg 

    Strengths of Ionic and Covalent Bonds

     

    1. Using the table of bond energies determine the approximate enthalpy change for each of the following reactions:
      1. \(\ce{H2}(g)+\ce{Br2}(g)⟶\ce{2HBr}(g)\)
      answer
      1. −114 kJ;
    2. Complete the following Lewis structure by adding bonds (not atoms), and then indicate the longest bond:

      A Lewis structure is shown that is missing its bonds. It shows a horizontal row of six carbon atoms, equally spaced. Three hydrogen atoms are drawn around the first carbon, two around the second, one above the fifth, and two by the sixth.

      answer

      A Lewis structure is shown. A carbon atom that is single bonded to three hydrogen atoms is bonded to a second carbon atom. The second carbon atom is single bonded to two hydrogen atoms. The second carbon atom is single bonded to a third carbon atom that is triple bonded to a fourth carbon atom and single bonded to a fifth carbon atom. The fifth carbon atom is single bonded to a hydrogen atom and double bonded to a sixth carbon atom that is single bonded to two hydrogen atoms.

      The C–C single bonds are longest.

    Molecular Structure and Polarity

    1. A molecule with the formula AB2, in which A and B represent different atoms, could have one of three different shapes. Sketch and name the three different shapes that this molecule might have. Give an example of a molecule or ion for each shape.
      answer

      Three Lewis diagrams are shown. The first diagram shows the letter A single bonded to the left and right to the letter B. An example, “C O subscript 2,” and the term, “linear,” are written beside this diagram. The second diagram shows the letter A with two lone pairs of electrons, single bonded to the left and lower right to the letter B. An example, “H subscript 2 O,” and the term, “bent with an approximately 109 degree angle,” are written beside this diagram. The third diagram shows the letter A with one lone electron pair, single bonded to the left and lower right to the letter B. An example, “S O subscript 2,” and the term, “bent with an approximately 120 degree angle,” are written beside this diagram.

    2. Predict the electron pair geometry and the molecular structure of each of the following molecules or ions:
      1. SF6
      2. PCl5
      3. (c) BeH2
      4. \(\ce{CH3+}\)
      answer
      1. Both the electron geometry and the molecular structure are octahedral.
      2. Both the electron geometry and the molecular structure are trigonal bipyramid.
      3. (c) Both the electron geometry and the molecular structure are linear.
      4. Both the electron geometry and the molecular structure are trigonal planar.
    3. Identify the electron pair geometry and the molecular structure of each of the following molecules:
      1. ClNO (N is the central atom)
      2. CS2
      3. (c) Cl2CO (C is the central atom)
      4. Cl2SO (S is the central atom)
      answer

      (a) electron-pair geometry: trigonal planar, molecular structure: bent (120°); (b) electron-pair geometry: linear, molecular structure: linear; (c) electron-pair geometry: trigonal planar, molecular structure: (d) trigonal planar; electron-pair geometry: tetrahedral, molecular structure: trigonal pyramidal

    4. Which of the following molecules have dipole moments?
      1. CS2
      2. SeS2
      3. (c) CCl2F2
      4. PCl3 (P is the central atom)
      5. ClNO (N is the central atom)
      answer

      SeS2, CCl2F2, PCl3, and ClNO all have dipole moments.

    5. Describe the molecular structure around the indicated atom or atoms:
      1. the sulfur atom in sulfuric acid, H2SO4 [(HO)2SO2]
      2. the chlorine atom in chloric acid, HClO3 [HOClO2]
      3. (c) the oxygen atom in hydrogen peroxide, HOOH
      4. the nitrogen atom in nitric acid, HNO3 [HONO2]
      answer

      (a) tetrahedral; (b) trigonal pyramidal; (c) bent (109°); (d) trigonal planar; bent (109°); 

    6. Use the Molecule Shape simulator to explore real molecules. On the Real Molecules tab, select H2O. Switch between the “real” and “model” modes. Explain the difference observed.
      answer

      The structures are very similar. In the model mode, each electron group occupies the same amount of space, so the bond angle is shown as 109.5°. In the “real” mode, the lone pairs are larger, causing the hydrogens to be compressed. This leads to the smaller angle of 104.5°.

    This page titled 8.E: Chemical Bonding and Molecular Geometry- Homework is shared under a CC BY license and was authored, remixed, and/or curated by Scott Van Bramer.