Intermolecular Force Activities Pure Substances and Mixtures: Parts I, II, III and IV

Students work in pairs in this classroom exercise to label and manipulate plastic arrows and rectangles to model intermolecular forces.  Students label eight white rectangles with types of particles and seven arrows with types of intermolecular forces.  They then are challenged to select and arrange the plastic tiles to correctly model given scenarios.

Activity 1 – Interactions between particles in pure substances: 

  1. Select two rectangular tiles of the same particle type.  (ex. ion and ion)   If the compound is ionic, write a "+" charge on the cation and a "-" charge on the anion.  If the compound is polar, i.e. has polar covalent bonds and has a net dipole moment, write a "partial positive charge" on one end and a "partial negative charge" on the other end of the rectangle.
  2. Place an arrow representing the appropriate particle interaction between the two rectangle particle tiles in such a way as to show there is an electrostatic force of attraction between the two particles.
  3. Repeat with the other three particle types.
  4. Sketch your representations as in the example shown below.  Include charges (either full or partial) on atoms involved in the IMF, show the appropriate alignment of particles in your sketch, use a dashed line to show the intermolecular force of attraction.

Activity 2 – Interactions between particles in a mixture (same as above but with two different substances)

Activity 3 – Interactions between real molecules in pure substances: KBr, ethane, ethanol, dimethy ether

  1. Select two rectangular tiles representing the same particle type.  (ex. a polar molecule)  if the compound is ionic, write a "+" charge on the cation and a "-" charge on the anion.  If the compound is polar, i.e. has polar covalent bonds and has a net dipole moment, write a "partial positive charge" on one end and a "partial negative charge" on the other end of the rectangle.
  2. Place an arrow representing the appropriate particle interaction between the two particle tiles in such a way as to show there is an electrostatic force of attraction between the two particles representing a pure substance. 
  3. Repeat for all of the other 3 possible combinations of particles. 
  4. Sketch your representations.  Include charges (either full or partial) on atoms involved in the IMF, show the appropriate alignment of particles in your sketch, use a dashed line to show the intermolecular force of attraction.

Activity 4 – Interactions between real molecules in a mixture: KBr, ethane, ethanol, dimethy ether

  1. Select two rectangular tiles representing different particle types.  (ex. ion and polar molecule)  if the compound is ionic, write a "+" charge on the cation and a "-" charge on the anion.  If the compound is polar, i.e. has polar covalent bonds and has a net dipole moment, write a "partial positive charge" on the atom having a partial positive charge and place this on one end of the rectangle representing a molecule.  Locate the atom in the other molecule having a partial negative charge and write the "partial negative charge" symbol next to the atom.  This atom should be on one end of the rectangle.  An example will be displayed in lecture.
  2. Place an arrow representing the type of IMF acting between the two particles.  Show the location of an electrostatic force of attraction between opposite charges.
  3. Repeat for all of the other combinations of particles. 
  4. Sketch your representations.  Include charges (either full or partial) on atoms involved in the IMF, show the appropriate alignment of particles in your sketch, use a dashed line to show the intermolecular force of attraction.
Curriculum Notes 

In an active learning setting, the first activity done by students prior to lecturing about IMFs can be used to provide an opportunity for students  "to construct and revise representations, models, and explanations that allow them to predict and explain phenomena."   Also, some students will have the opportunity to evaluate and consolidate their mastery of the various models associated with intermolecular forces.

In a traditional classroom, these series of activities might serve the same functions immediately following an expository lecture on intermolecular forces.

Student Difficulties with IMF

1.  Students exhibit difficulty with the concept of an Intermolecular Force being a force of attraction, an electrostatic interaction, between two or more molecules.  The majority of students will identify an IMF as an interaction within a molecule, or the identification is ambiguous or contradictory.

Learning Objectives

1.  Identification of the atoms in a molecule having a partial positive charge or a partial negative charge: bond polarity.

2. Identification of an intermolecular force as an electrostatic force of attraction between two or more molecules.  The forces responsible for keeping molecules or atoms intact as a solid or liquid are intermolecular forces. 

3.  Identification of the location(s) and type of an intermolecular force between two or more molecules as represented by white plastic rectangles and yellow plastic arrows

5. Identification and correlation of different IMFs with physical properties: melting point, boiling point, heat of vaporization, etc.  The strength of the IMF(s) interactions between molecules in a solid or liquid determines its physical state and determines its physical properties.

6. The distinction between a chemical bond (within a molecule) and an intermolecular force (between two or more molecules) using Coulomb's Law and the van der Waals radius of atoms.

7. Students  have the opportunity to construct and revise representations, models, and explanations that allow them to predict and explain phenomena.

Literature Articles Related to Student Difficulties with IMF

1. Copper, M; Williams, L. C., Underwood, S. M. Student understanding of Intermolecular Forces: A multi-modal study.  Journal of Chemical Education, v92 n8 p1288-1298 Aug 2015. (EJ1073053)

Quotes:  "It is our contention that, to develop a robust understanding, the curriculum must be restructured to emphasize the connections between important ideas and that students must be given opportunities to reflect on and make their thinking visible (Ref#45)  That is, students must have the opportunity to construct and revise representations, models, and explanations that allow them to predict and explain phenomena. Otherwise, it becomes too easy to assume that students have learned important concepts because they can choose the correct answer on an examination."

 "If students are not ever asked to write and draw, to reflect, to explain, and to revise their ideas, but instead are only assessed by which item they choose on a test or randomly generated homework, it is unlikely that they will develop a robust and coherent understanding of core concepts. This is not to say that multiple-choice items are never useful  but that students must also be given many opportunities to construct answers for themselves as they learn.."

Lead Time 
Three days of lead time is required for this project.
Materials 

Up to 200 sets of:

  • seven plastic double-sided arrows
  • eight plastic rectangles
  • two fine-point dry-erase markers
  • one metal case
Procedure 

See downloadable instructions in the sidebar.

Footnotes 

References

1. Copper, M; Williams, L. C., Underwood, S. M. Student understanding of Intermolecular Forces: A multi-modal study.  Journal of Chemical Education, v92 n8 p1288-1298 Aug 2015. (EJ1073053)

2. Schmidt, H.-J.; Kaufmann, B.; Treagust, D. F. Students’ Understanding of Boiling Points and Intermolecular Forces. Chem. Educ. Res. Pract. 2009, 10, 265272. 

3. Bruck, L. A Hands-on Activity to Build Mastery of Intermolecular forces  and Its Impact on Student Learning. Journal of College Science Teaching, v45 n4 Mar 2016. 9 pp.    Abstract: The intermolecular forces activity presented in this article is designed to foster concept-building through students' use of concrete, manipulative objects, and it was developed to be pedagogically sound. Data analysis via pre- and posttesting and subsequent exam questions indicated that students who had the opportunity to participate in the activity were better able to identify and apply intermolecular forces both immediately after completion of the activity and also at the end of the semester.

© Copyright 2012 Email: Randy Sullivan, University of Oregon Chemistry Department and UO Libraries Interactive Media Group