Surface Tension of Water

3-D Molecular Designs
Type Category
Instructional Materials
Activity , Instructor Guide/Manual
This resource, vetted by NSTA curators, is provided to teachers along with suggested modifications to make it more in line with the vision of the NGSS. While not considered to be “fully aligned,” the resources and expert recommendations provide teachers with concrete examples and expert guidance using the EQuIP rubric to adapted existing resources. Read more here.


This lesson plan (pages 14-15 of the Water Basic Lesson Plan) provides teacher guidelines for using 3-D water and ethanol molecule models to explain water’s surface tension property that results from the polar nature of the molecules by comparison with non-polar molecules. The lesson is initiated by having students observe phenomenon related to surface tension and then use 3-D molecules to model the behavior. The water kit required for this activity is available on loan for free from the Milwaukee School of Engineering Center for BioMolecular Modeling ( or for purchase from 3-D Molecular Designs.

Intended Audience

Educational Level
  • Grade 12
  • Grade 10
  • Grade 11
  • Grade 9
  • High School
Access Restrictions

Free access - The right to view and/or download material without financial, registration, or excessive advertising barriers.

Performance Expectations

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.

Clarification Statement: Emphasis is on understanding the strengths of forces between particles, not on naming specific intermolecular forces (such as dipole-dipole). Examples of particles could include ions, atoms, molecules, and networked materials (such as graphite). Examples of bulk properties of substances could include the melting point and boiling point, vapor pressure, and surface tension.

Assessment Boundary: Assessment does not include Raoult’s law calculations of vapor pressure.

This resource is explicitly designed to build towards this performance expectation.

Comments about Including the Performance Expectation
The molecule models allows for students to compare forces between particles of different molecules, water, ethane, and ethanol. The water molecules in the model kit contain magnets to simulate their polarity while the ethane molecules do not contain magnets and the ethanol molecules are only magnetic on the end with the –OH functional group. In this way, students will investigate how the difference in the electrical forces between particles in these substances causes differences in their properties. The initial exploration outlined in this lesson could be extended to include wet lab work designed to compare the surface tension properties of water to other substances in the liquid state (alkanes or alcohols). This would help students connect the investigation with observations of a wider range of bulk scale properties, not just water. The wet lab work would be best completed before the work with the 3-D models, but could also be done during the work with the molecules or afterwards. It is important that before students investigate surface tension (or other properties) with these molecule kits the teacher emphasize differences in magnetic forces between the molecule models and electrical forces between actual molecules. Suggestions for explaining this difference to students are provided on pages 5-7 of the lesson guidelines.

Science and Engineering Practices

This resource is explicitly designed to build towards this science and engineering practice.

Comments about Including the Science and Engineering Practice
While the PE from the standards is about planning and conducting an explanation, the use of the 3-D molecules is better used for generating data to support explanations for the phenomenon of surface tension. To best engage students in the practice of using the model to generate data to support their explanation, students need to be pushed to use the observations from using the molecules to explain the observed phenomena that are included in the lesson: water bubbling up on wax paper, water bugs ability to walk on water, or paper clips that can sit atop water but not ethanol. The teacher should work to maintain the focus of the work with the molecules on explaining these phenomena. Using this lesson plan within a larger unit will help build students’ capacity for making inferences about the electrical forces between the atoms/molecules in that substance. Used in this way, the lesson supports students in designing their own investigations to examine bulk scale properties of different substances.

Disciplinary Core Ideas

This resource is explicitly designed to build towards this disciplinary core idea.

Comments about Including the Disciplinary Core Idea
To further emphasize the connection between the bulk scale observations and the forces between the molecules, students should have access to water and ethanol during their work with the 3-D models. As noted above, it is important for the teacher to be explicit about the differences in magnetic forces between the molecules in the 3-D model kit and the electrical forces between real atoms/molecules. It would be beneficial for students to complete an Analogy Map (see BSCS to be address this in the classroom.

Crosscutting Concepts

This resource is explicitly designed to build towards this crosscutting concept.

Comments about Including the Crosscutting Concept
The combination of observing the phenomena that demonstrate water’s polar nature and using the 3-D molecules allows students to examine both the bulk scale and the molecular-level. It is important to help students connect these levels of representation and expect them to explain the connections in verbal explanations. That is, students’ explanations of how the electrical forces between molecules affects the properties of the substance should include evidence from both scales. Students do this by recording observations of the water droplet and paperclip activities at the bulk level, and the plastic bug resting on the model kits to simulate the molecular level.

Resource Quality

  • Alignment to the Dimensions of the NGSS: While the lesson plan outlined is brief, the practice of using models for investigating this disciplinary core idea are explicit in this outline. The lesson could be further strengthened with connections to observation of natural phenomena to provide context and connect to the experience of learners, like a video of a water bug moving across water.

  • Instructional Supports: The brief lesson plan includes questions for the teacher to pose to students. Additional support is needed for providing differentiated opportunities for students to clarify and justify their ideas and respond to peer and teacher feedback in ways that support their learning. Teachers are encouraged to anticipate what students will struggle with and plan questions to pose that will connect to students' experiences while maintaining cognitive demand in the lesson.

  • Monitoring Student Progress: The lesson plan does not provide an explicit method for monitoring student progress. Teachers may want to use an exit card or other formative assessment strategy to assess student understanding of the connection between the observations they had made at the bulk scale with the 3-D models. The lesson plan could also be broken up to allow the teacher to monitor student progress throughout the class so that they can adjust their instruction as necessary. Additionally, students should be provided differentiated support with tools or suggestions for recording their observations with drawings and descriptions. Students would then refer to these to connect molecular representations to the observations at the bulk scale during the wet lab activities.

  • Quality of Technological Interactivity: This resources is a document for teachers and does not include suggestions for technology in support of student learning.