Chemistry · 10th Grade

Active learning ideas

Intermolecular Forces (IMFs): London Dispersion Forces

Active learning works because London Dispersion Forces are counterintuitive. Students often think weak forces can’t explain real-world behavior like state changes, so hands-on ranking and drawing help them see how tiny temporary charges add up to measurable effects.

• Common Core State Standards
• STD.HS-PS1-3
• STD.HS-PS3-2

• 25–35 min
• Pairs → Whole Class
• 3 activities

Activity 01

• Think-Pair-Share
• 25 min · Pairs

Think-Pair-Share: Predicting Boiling Points

Students receive a table of six nonpolar molecules with their molecular formulas and molar masses (e.g., F2, Cl2, Br2, I2, CH4, C4H10). Individually, they rank the molecules by predicted boiling point. Pairs compare rankings and must agree on a single ranked list, defending their reasoning. The class compares to actual data and discusses what the data reveals about electron count and LDF strength.

Explain the origin of London Dispersion Forces (LDFs).

Facilitation Tip

During Think-Pair-Share, assign roles so quieter students summarize the group’s prediction before sharing with the class.

What to look for

Provide students with a list of small, nonpolar molecules (e.g., CH4, C2H6, C3H8). Ask them to rank these molecules from lowest to highest boiling point and justify their ranking by referencing LDF strength and molecular size.

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Activity 02

• Inquiry Circle
• 35 min · Small Groups

Inquiry Circle: Shape Matters

Groups compare pairs of isomers (n-butane vs. isobutane, n-pentane vs. neopentane) with identical molecular formulas. Using molecular models or 3D drawings, they determine which isomer has greater surface area and predict which has the higher boiling point. Groups share predictions before the teacher reveals actual boiling point data, prompting a discussion about why compact shapes reduce LDF strength.

Analyze how molecular size and shape affect the strength of LDFs.

Facilitation Tip

For the Collaborative Investigation, give each group a molecular model kit and one large sheet of chart paper to record observations.

What to look for

Pose the question: 'Why does iodine (I2), a solid at room temperature, have a much higher boiling point than chlorine (Cl2), a gas?' Guide students to discuss the role of electron count and polarizability in determining LDF strength.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 03

• Gallery Walk
• 30 min · Pairs

Gallery Walk: IMF Strength Ranking

Posters around the room each show a set of three nonpolar molecules. Students rotate and rank each set by expected boiling point, leaving a sticky note explaining which molecular property drove their prediction. In the debrief, the teacher highlights cases where students chose mass versus polarizability as their reasoning and unpacks which factor is more predictive.

Predict the relative boiling points of nonpolar molecules based on LDFs.

Facilitation Tip

In the Gallery Walk, post ranking charts with a blank row at the bottom for student-added molecules or corrections.

What to look for

Students draw two molecules of the same nonpolar substance. On their drawing, they must illustrate how an instantaneous dipole forms in one molecule and induces a dipole in the other, labeling the partial charges and the resulting LDF.

• Understand
• Apply
• Analyze
• Create
• Relationship Skills
• Social Awareness

A few notes on teaching this unit

Teachers should move from concrete to abstract by starting with macroscopic properties like boiling points before drawing partial charges. Avoid spending too much time on formal definitions of polarizability; instead, let students discover the concept through data. Research suggests students grasp LDFs better when they compare isomers of the same mass, which shows shape matters more than molar mass alone.

Successful learning looks like students using molecular size, shape, and electron count to explain why substances with only LDFs have different boiling points. They should connect temporary dipoles to observable properties like state at room temperature.

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Watch Out for These Misconceptions

• During Think-Pair-Share: Predicting Boiling Points, watch for students who assume all nonpolar molecules must be gases because they see CH4 and C2H6 as gases in class examples.

  Use the Think-Pair-Share prompt to introduce heavier nonpolar molecules like C8H18, which is a liquid, and have groups revise their predictions using molar mass and LDF strength.

• During Collaborative Investigation: Shape Matters, watch for students who conflate LDFs with permanent dipoles when discussing why branched alkanes have lower boiling points than straight-chain alkanes.

  Prompt groups to compare electron distribution diagrams of isomers and explicitly label temporary versus permanent dipoles before they finalize their shape-based rankings.

• During Gallery Walk: IMF Strength Ranking, watch for students who assume heavier molecules always have stronger LDFs without considering shape or surface area.

  Require groups to add a written explanation next to each ranking, citing polarizability and molecular geometry, and have peers challenge unclear explanations during the walk.

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Methods used in this brief

• Think-Pair-Share
• Inquiry Circle
• Gallery Walk