Molecules in Motion

American Chemical Society
Type Category
Instructional Materials
Lesson/Lesson Plan , Simulation , Activity
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 (1.2) is the second lesson in Chapter 1: Matter-Solids, Liquids, and Gases from Middle School Chemistry produced by ACS. The lesson, which is outlined comprehensively in the lesson plan, follows the BSCS 5E Instructional Model. It begins with a series of questions as a way of helping students design an experiment to see if the speed of molecules is different in hot water compared to cold water. A well described experiment follows. The simulation that illustrates water molecules at different temperature is introduced to explain the observations in the experiment. The explanation is extended to explain why hot water takes up more space than room temperature water. The website includes downloadable pdf documents for the lesson plans, the entire chapter, student activity sheets, the answer sheet for the activity sheet, and a student reader to be used at the end of the lesson.

Intended Audience

Educational Level
  • Middle School
Access Restrictions

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

Performance Expectations

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.

Clarification Statement: Emphasis is on qualitative molecular-level models of solids, liquids, and gases to show that adding or removing thermal energy increases or decreases kinetic energy of the particles until a change of state occurs. Examples of models could include drawing and diagrams. Examples of particles could include molecules or inert atoms. Examples of pure substances could include water, carbon dioxide, and helium.

Assessment Boundary: none

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

Comments about Including the Performance Expectation
The lesson plan and simulation address the motion of molecules related to temperature for liquids but not change of state. Temperature is not related to thermal energy. Other lessons later in the unit address change of state. This lesson should be considered as one lesson leading to a complete understanding of the outcome in the performance expectation.

Science and Engineering Practices

This resource appears to be designed to build towards this science and engineering practice, though the resource developer has not explicitly stated so.

Comments about Including the Science and Engineering Practice
An animation/simulation is introduced in the lesson to explain the phenomena the students have observed in their experiment. The term or concept of a model is not introduced but the idea that the animation is only a representation of the real molecules should be pointed out. A description of a model could be introduced at this point together with the advantages and limitations of this particular model. Students are asked to draw a model to describe the molecular level motion of the water in question 6, which is scaffolded to ask about the distance of the molecules and the amount of motion lines drawn.

Disciplinary Core Ideas

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

Comments about Including the Disciplinary Core Idea
The lesson does an adequate job of meeting the core idea for liquids. An additional lesson is needed to complete the disciplinary core idea of gases. A suitable lesson for this purpose is lesson 5, Air, is it really there? in this chapter

Crosscutting Concepts

This resource appears to be designed to build towards this crosscutting concept, though the resource developer has not explicitly stated so.

Comments about Including the Crosscutting Concept
The fact that the temperature change is causing the change in motion (effect) needs to be explicitly pointed out to the students. This language can easily be added to the lesson plan.

Resource Quality

  • Alignment to the Dimensions of the NGSS: The explicit use of DCI is well addressed in the lesson. The opportunity to make sense of phenomena is inherent in the use of the BSCS 5E model but the lesson plan simply calls for the use of the simulation immediately following the investigation and does not ask the students to create their own model before revealing the accepted model.

  • Instructional Supports: The comprehensive and detailed lesson plan provides excellent instructional support for the lesson as it is designed. It should be modified to have a more explicit conversation about the simulation as a model, and how the temperature and motion relationship is a idea of cause and effect relationship in the explanation phase of the lesson.

  • Monitoring Student Progress: The lesson does not provide an explicit method for monitoring student progress. However, a teacher could check in with a lab group as they are making observations and ask probing questions while they working through their analysis. There is a test bank of questions for the entire chapter of which this lesson is a part. A number of those questions are applicable to this lesson.

  • Quality of Technological Interactivity: Although very simple, the simulation is straightforward and easy to manipulate. It is a simulation for liquids only. This simulation can be downloaded as an SWF file to be used without an internet connection.