ntermolecular Forces and Properties of Substances

Answer all the right answers to the questions.

Intermolecular Forces and Properties of SubstancesObjectives

This lab has two parts. In successfully completing this lab you will:

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  1. Review polarity of molecules using a PhET simulation, and predict how polarity will determine the types of intermolecular forces and properties of atoms/molecules. 
  2. Investigate the different intermolecular forces, and how microscopic properties affect the macroscopic behavior of substances.


Understanding the properties of substances is crucial to designing laboratory experiments. Many properties of liquids and solids are affected by the intermolecular forces experienced by these substances. The type and strength of the intermolecular forces a molecule will experience is largely related to the polarity of the molecule. For lab this week we review polarity, and explore intermolecular forces. We will also investigate how intermolecular forces affect various properties of substances.Experiment Part 1: Polarity and Intermolecular Forces

Using the PhET simulation “Molecule Polarity”.

Adapted from “Intermolecular Forces and Molecules” by Ted Clark and Julia Chamberlain. (CC by 4.0) Link to original file here.

  1. At the bottom of the screen, choose Three Atoms.
  2. Under View, click the boxes so that Bond Dipoles, Molecular Dipole, and Partial Charges are all showing.
  3. Atoms A and C should have the electronegativity all the way to the left (less), and Atom B should have the electronegativity in the middle.
  4. Answer the following questions:
    1. What is the molecular shape of the molecule shown?
  1. Which atom(s) is more electronegative?
  1. Which atom(s) has the partial negative charge(s)?
  1. Which atom(s) has the partial positive charge(s)?
  1. Where do the bond dipoles point?
  1. Where does the molecular dipole point?
  1. How is the molecular dipole related to the bond dipoles?
Answer all the right answers to the questions. 1
  1. How is the electrostatic potential (charge distribution) of CO2 different than H2?
  2. Do these results support your predictions?
  3. What would predict the electrostatic potential to look like for SO2? Would it have positive and negative regions? Where would these be?
  4. Identify the molecules that would exhibit H-bonding in the following examples. What do you notice about the electrostatic potential of those molecules compared to those that do not exhibit H-Bonding?
Answer all the right answers to the questions. 2
  1. What types of IMFs would you expect Ne, Ar and O2 to have? Why?
  1. The following picture was taken from a different PhET simulation on states of matter. Which substance has the weakest intermolecular force? Explain your reasoning.
Answer all the right answers to the questions. 3
  1. Explain the differences in boiling points for the following molecules:
Answer all the right answers to the questions. 4

Part 2: Intermolecular Forces and Properties

Polarity affects the type and strength of intermolecular forces a substance will experience. In turn, the strength of intermolecular forces affect some properties of the substance. We will now investigate this further by looking at the different types of intermolecular forces, various substances, and their properties. Please use the data provided to answer the questions. Then, use your observations to make predictions about properties of substances.

Intermolecular Forces and Evaporation

In order for molecules to evaporate from the surface of a liquid, they must have enough kinetic energy (obtained from collisions with neighboring molecules) to break the attractions (intermolecular forces) they have for their neighbors. When the molecules escape from the gas phase, they carry this kinetic energy away with them. Therefore, evaporation is an endothermic process that cools the remaining liquid.

Figure 1: Evaporation of liquid particles.

Answer all the right answers to the questions. 5

Molecules that are not very sticky (i.e. those that have small intermolecular forces) can evaporate rapidly, causing the temperature of the liquid to drop quickly. Conversely, molecules with strong intermolecular forces will not experience much evaporation and little cooling will be observed. 

The change in temperature during a two minute evaporation period was recorded for several substances and organized in the table below. Use the following data to answer the next few questions:

Table 1: Change in Temperature During Evaporation and Total Number of Electrons in Various Hydrocarbons.

CompoundChange in T during evaporation (0C)Total number of electrons in compound
decane (C10H22)-1.482
nonane (C9H20)-2.874
octane (C8H18)-5.166
heptane (C7H16)-9.558
hexane (C6H14)-14.550
pentane (C5H12)-22.042

1. The compound with the strongest intermolecular forces is ________. The compound with the weakest intermolecular forces is ________. 

2. All of these compounds are polar/nonpolar (circle one). The predominant intermolecular force found in these substances is ________.

3. Based on the data above, the more/less electrons a substance has, the stronger the __________.

Compare two liquids: acetone (C3H6O) and 2-butanone (C4H8O). 

4. Of the two liquids above, ________ would have the stronger intermolecular forces.

5. Of the two liquids above, ________ would show the greater change in temperature during evaporation in a two minute time period.

Intermolecular Forces and Boiling Point

The boiling point is the temperature at which the liquid and gas exist in equilibrium. At this temperature the liquid molecules have gained enough energy to overcome the attractive intermolecular forces and escape into the gas phase. Also at this temperature, the gas molecules have lost enough energy to succumb to the intermolecular attractive forces and condense into the liquid phase. Use the following table to answer the questions below:

Table 2: Structures, Molecular Weight and Boiling Points of Several Substances. 

CompoundStructureMolecular Weight (g/mol)Boiling Point (0C)

1. Pentane is a polar/nonpolar molecule. The predominant intermolecular force in pentane is LDF/D-D/H-Bonding. (Circle one)

2. 1-butanol is a polar/nonpolar molecule. The predominant intermolecular force in 1-butanol is LDF/D-D/H-Bonding. (Circle one)

3. 2-butanone is a polar/nonpolar molecule. The predominant intermolecular force in 2-butanone is LDF/D-D/H-Bonding. (Circle one)

4. Rank the three principle intermolecular forces in order of weakest to strongest.

5. The stronger the intermolecular force, the lower/higher the boiling point. (Circle one)

6. Pentane, 1-butanol and 2-butanone share an intermolecular force that is approximately the same strength for all three compounds. What is the intermolecular force, and why is it approximately the same strength for all three compounds. Explain.

7. Draw Lewis Structures for acetone (C3H6O), butane (C4H10) and isopropanol (C3H8O) and determine the predominant intermolecular force in each compound. Use the structures to predict the boiling points given the data below:

CompoundBoiling Point (0C)

Please show all work below.

8. Explain your answers for Question 7. Why did you place each compound where you did?

9. Draw Lewis Structures of the following compounds and determine their predominant intermolecular forces:

1. ethane (C2H6)

2. ethylene glycol (CH2OHCH2OH)

3. propane (C3H8)

4. ethanol (CH3CH2OH)

5. dimethyl ether (CH3-O-CH3)

Use the structures to predict the boiling points given the data below:

CompoundBoiling Point (0C)

Please show all work on next page.

Lewis Structures for Question 9:

10. Explain your answers for Question 9. Why did you place each compound where you did? 

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