Intermolecular Forces Investigation
Teacher Notes & Alignment
Estimated Time: 45 minutes Materials: Internet-connected device per student/group, simulation link, printed/digital handout.
Performance Expectation: 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.
Science and Engineering Practice: Planning and Carrying Out Investigations Disciplinary Core Idea: PS1.A: Structure and Properties of Matter Crosscutting Concept: Patterns
Evidence Statements Addressed:
- 1. Identifying the phenomenon: Students describe the relationship between bulk properties (boiling point, surface tension) and the strength of electrical forces between particles.
- 2. Identifying the evidence: Students describe why data on bulk properties provides information about intermolecular forces, noting that thermal energy opposes electrical attractions.
- 3. Planning for the investigation: Students write an investigation plan detailing the data to be collected.
- 4. Collecting the data: Students use the simulation to record bulk properties for different substances.
- 5. Refining the design: Students evaluate the simulation’s limitations as an experimental model.
Part 1: Engage (Anchoring Phenomenon)
Phenomenon: If you place a drop of water (H₂O) on a penny, it forms a tall, rounded bead. If you place a drop of acetone (C₃H₆O) on a penny, it immediately flattens out and evaporates much faster.
- Based on this phenomenon, what differences might exist between the molecules of water and the molecules of acetone?
- What “need to know” questions do you have about how molecules interact with each other?
Part 2: Explore (Simulation Investigation)
Objective: Plan and conduct an investigation using the simulation to determine how the strength of intermolecular forces affects the bulk properties of different substances.
Available Simulation Tools:
- Substance Selection: Three unknown substances (A, B, and C) with different polarities.
- Heat Energy Input (Temperature): A slider to increase the thermal energy of the system.
- Observations: A droplet view showing surface tension, and a molecular view showing particle spacing as they transition to vapor.
- Data Outputs: Boiling point, relative IMF strength, and a vapor curve chart.
Your Task:
- Develop an Investigation Plan: Write a brief plan for how you will use the simulation to collect data on all three substances. Detail what you will change (independent variable) and what you will measure or observe (dependent variables).
- Collect Data: Follow your plan to collect data. Record your observations in a table similar to the one below.
| Substance | Polarity Type | Boiling Point (°C) | Surface Tension (Droplet Shape) | Relative IMF Strength |
|---|---|---|---|---|
| A | ||||
| B | ||||
| C |
Part 3: Explain (Sensemaking)
Using the data you collected, answer the following questions:
- Patterns in the Data: What is the relationship between the strength of intermolecular forces and a substance’s boiling point?
- Particle-Level Explanation: Describe what happens to the spacing between particles when heat energy is added to the system. Why does a substance with stronger intermolecular forces require a higher temperature to boil?
- Surface Tension: How does the droplet shape (surface tension) reflect the patterns of interaction between particles at the molecular scale?
Part 4: Elaborate/Evaluate (Argumentation & Modeling)
- Scientific Argument: Construct a scientific argument answering this question: How do electrical forces between particles determine the macroscopic bulk properties of a substance?
- Claim: State a direct answer to the question.
- Evidence: Use specific data from your investigation (e.g., boiling points, droplet shapes, thermal energy required) for Substances A, B, and C.
- Reasoning: Explain why the evidence supports your claim using the concepts of kinetic (thermal) energy and intermolecular electrical attractions.
- Evaluate the Model: What are the limitations of this simulation as an experimental model for testing intermolecular forces? How might you refine your investigation plan if you were conducting it in a real laboratory?