Summary

In this activity, students will view an animation that explores the relationship between physical properties and particle-level interactions. Particle diagrams of common household substances are used to illustrate that forces of attraction influence melting points. Similarly, particle diagrams of the same substances dissolved in water are used to compare their conductivity in solution.

Grade Level

Middle School, High School

NGSS Alignment

This activity will help prepare your students to meet the performance expectations in the following standards:

• MS-PS1-1: Develop models to describe atomic composition of simple molecules and extended structures.
• MS-PS1-4: Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
• HS-PS1-3: Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
• Scientific and Engineering Practices:
  • Developing and Using Models
  • Analyzing and Interpreting Data
  • Planning and Carrying Out Investigations

Objectives

By the end of this activity, students should be able to:

• Describe how particle interactions differ between ionic and molecular compounds and how this leads to different physical properties.

Chemistry Topics

This activity supports students’ understanding of:

• Physical properties
• Intermolecular forces
• Ionic and covalent bonding

Time

Teacher Preparation: minimal

Lesson: 10-30 minutes

Materials

• Computer and projector with internet access
• https://teachchemistry.org/classroom-resources/physical-properties-and-particle-interaction-animation
• Student handout

Safety

• No specific safety precautions need to be observed for this activity.

Teacher Notes

• All of the animations that make up the AACT Animation collection are designed for teachers to incorporate into their classroom lessons. Intentionally, these animations do not have any spoken explanations so that a teacher can speak while the animation is playing and stop the animation as needed to instruct.
• If you assign this to students outside of class time, you can create a Student Pass that will allow students to view the animation (or any other video or ChemMatters article on the AACT website).
  
• We suggest that a teacher pause this animation at several points, including when questions are posed before the answers are revealed, or watch it more than once to give students the opportunity to make notes, ask questions, and test their understanding of the concepts presented. It may be particularly useful to replay the particle diagrams shown at several points throughout the animation. The student activity sheet can help guide students through the animation and focus their attention on key points in the video.
• This animation centers around trying to distinguish between common and similar-looking kitchen materials table salt and sugar. Be sure to emphasize the point made in the opening of the video that chemicals in a lab cannot be tasted, but there are other ways to differentiate between materials with similar appearances.
• The animation shows how differences in melting point and conductivity in solution can be used to differentiate between the two compounds because salt is ionic and sugar is molecular, which results in different properties. Salt, the ionic compound, is made up of charged ions which take a lot more energy to separate from each other, thus resulting in a very high melting point. Sugar molecules are electrically neutral and not as strongly attracted to one another as positive ions to negative ions. They are easier to separate from one another, thus sugar’s lower melting point. Both substances will dissolve in water, but only the salt solution will conduct electricity, turning the lightbulb on in the conductivity test.
• Note that actually melting table salt would require a very high temperature and specialty equipment. If you wanted to add a demo piece to this lesson, you could use a hot plate to heat two beakers, one containing salt and one containing sugar. Students will see how the sugar melts but salt does not, as it would need to get much hotter than the hot plate can go. If the sugar is allowed to continue to be heated, it could caramelize and eventually decompose, which could introduce a discussion about chemical changes.
  • Some molten salts are being used as heat transfer fluids in concentrating solar power plants because of their ability to retain large amounts of heat, which is then used to turn water into steam that turns turbines to generate electricity! However, there are lots of challenges associated with keeping these plants running.
• Another demo or mini-lab for students would be to use conductivity testers on samples of sugar water and salt water to see which one conducts electricity. (Note that if you use tap water instead of distilled water, the light bulb may turn on for the sugar water, even though it theoretically shouldn’t conduct electricity, because of the presence of other dissolved ions in the tap water – this presents a good way to discuss experimental error, contamination of materials, the ability of water to dissolve many different materials, etc.)
• To keep the focus of the conductivity test on the particles in question (sodium and chloride ions and sucrose molecules), the particle diagrams that involve solutions use a simplified water molecule (a blue circle), and in reality, there would be many more water molecules. Additionally, a battery (not shown) would need to be connected to the circuit for the lightbulb to turn on. This would be a good opportunity to discuss the benefits and limitations of models in chemistry.
• In the conductivity test section, point out that the positive sodium ions (purple circles) and negative chloride ions (green circles) are moving in opposite directions in the solution, which is what allows the electricity to flow. The electrically neutral sucrose molecules don’t move in any particular direction and that solution does not conduct electricity.
• The second set of example materials includes two other materials that might be found in a kitchen – potassium chloride is used as a salt substitute, and lauric acid is a component of coconut oil. To include more hands-on chemistry, these two substances could be provided but not identified and students could determine which is which based on the properties described in the animation.
• Classroom resources from the AACT Library that may be used to further teach this topic include:
• Simulation: Intermolecular Forces
• Unit Plan: Chemical Bonding Unit Plan
• Lab: Ionic vs. Covalent Compounds
• Lesson Plan: Investigating Properties of Ionic and Covalent Compounds
• Demonstration: Intermolecular Forces and Physical Properties
• Lab: Microscopic Wonder
• Demonstration: Interactions Between Particles