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Bonding Free-Response Questions for AP Chemistry

based on 6 ratings
By — McGraw-Hill Professional
Updated on Feb 9, 2011

Review the following concepts if necessary:

Questions

First Free-Response Question

Answer the following questions. You have 15 minutes, and you may not use a calculator. You may use the tables at the back of the book.

Answer each of the following with respect to chemical bonding and structure.

  1. The nitrite ion, NO2, and the nitrate ion, NO3, both play a role in nitrogen chemistry.
    1. Draw the Lewis (electron-dot) structure for the nitrite ion and the nitrate ion.
    2. Predict which ion will have the shorter bond length and justify your prediction.
  2. Using Lewis (electron-dot) structures, explain why the ClF3 molecule is polar and the BF3 molecule is not polar.
  3. Consider the following substances and their melting points:
  4. Explain the relative values of the melting points of these substances.

Second Free-Response Question

Answer the following questions. You have 15 minutes, and you may not use a calculator.You may use the tables in the back of the book.

Answer the following questions about structure and bonding.

  1. Which of the following tetrafluorides is nonpolar? Use Lewis electron-dot structures to explain your conclusions.
      SiF4   SF4   XeF4
  2. Rank the following compounds in order of increasing melting point. Explain your answer. Lewis electron-dot structures may aid you.
  3. SnF2   SeF2   KrF2
  4. Use Lewis electron-dot structures to show why the carbon–oxygen bonds in the oxalate ion (C2O4 2–)are all equal.
  5. When PCl5 is dissolved in a polar solvent, the solution conducts electricity. Explain why. Use an appropriate chemical equation to illustrate your answer.

Answers and Explanations

First Free-Response Question

  1.  
    1. Give yourself 1 point for each structure that is correct. The double bonds could be between the nitrogen and any of the oxygens, not just the ones shown. Only one double bond per structure is allowed.

    2. If you predicted the nitrite ion has the shorter bond length, you have earned 1 point.
    3. The explanation must invoke resonance. You do not need to show all the resonance structures. You need to mention that the double bond "moves" from one oxygen to another. In the nitrite ion, each N–O bond is a double bond half the time and a single bond the other half. This gives an average of 1.5 bonds between the nitrogen and each of the oxygens. Similarly, for the nitrate ion, each N–O bond spends one-third of the time as a double bond, and two-thirds of the time as a single bond. The average N–O bond is 1.33. The larger the average number of bonds, the shorter the bond is. This explanation will get you 1 point.

  2. Give yourself 1 point for each correct Lewis structure.
  3. The BF3, with three bonding pairs and zero nonbonding pairs on the central atom, is not polar. The ClF3, with five pairs about the central atom, is polar because of the two lone pairs. Give yourself 1 point for this explanation.

  4. You get 1 point for saying that the two compounds with the highest melting points are ionic and the other compounds are molecular.
  5. You get 1 point if you say that SrS is higher than KCl because the charges on the ions in SrS are higher.

    You get 1 point if you say H2O is higher than the lowest two because of hydrogen bonding.

    You get 1 point if you say H2S is higher than CH4 because H2S is polar and CH4 is nonpolar.

    There are a maximum of 11 points.

Second Free-Response Question

  1. Silicon tetrafluoride is the only one of the three compounds that is not polar.
  2. Bonding Free Response Questions

    You get 1 point if you correctly predict only SiF4 to be nonpolar. You get 1 additional point for each correct Lewis structure.

  3. The order is: KrF2 < SeF2 < SnF2.
  4. Bonding Free Response Questions

    The Lewis structure indicates that KrF2 is nonpolar. Thus, it only has very weak London dispersion forces between the molecules. SeF2 is polar and the molecules are attracted by dipole–dipole attractions, which are stronger than London. SnF2 has the highest melting point, because of the presence of strong ionic bonds.

    You get 1 point for the order, and 1 point for the discussion.

  5. The following resonance structures may be drawn for the oxalate ion. The presence of resonance equalizes the bonds.
  6. Bonding Free Response Questions

    You get 1 point for any correct Lewis structure for C2O42–,and 1 point for showing or discussing resonance.

  7. PCl5 must ionize. There are two acceptable equations.
  8. You get 1 point for the explanation, and you get 1 point for either of the equations. Total your points for the different parts. There are 10 points possible.

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