Molecules Matter

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SWBAT: Model the interactions of water at the molecular level.

Big Idea

Students see that matter is composed of tiny objects that are attracted to one another.

Key Concepts for Unit 1

Chapter 1, Lesson 1: Molecules Matter

Key Concepts

• Chemistry is the study of matter.

• Matter is made up of extremely tiny particles called atoms and molecules.

• Atoms and molecules make up the three common states of matter on Earth — solids,

liquids, and gases.

• The particles of a liquid are attracted to one another, are in motion, and are able to move

past one another.

• Being a solid, liquid, or gas is a property of a substance.

These topics are more generally addressed in the KWL chart that students receive as the do now activity.

Do Now

5 minutes

This lesson is modified with permission from the American Chemical Society.  

Students fill in the KWL as they enter the room.  This KWL is used to serve as a continual source of reflection for students.  As students discover more information about matter, they go back to the What I Learned section to update the KWL.  Additionally, they refer to the What I Want to Know to see if their questions are being answered.  


5 minutes

Now students Think-Pair-Share with elbow partners. I ask them to think about the word matter and make a list of words that come to mind when they hear that word -- reminding them to hold on to what might be changing in their thinking so that they can update their KWL. (You might want to have a student or two share at the end if they have any "changes in thinking" to report.)

I then have students share with their partners.  Partner groups try to come up with a definition for chemistry. Then, partners share out to the class.  We try to come up with a definition for matter that makes sense.

Definition of matter: anything that takes up space and has mass. Students have already done the mass vs. weight lesson, so I ask them to give the key concept of that lesson. Students remember that mass is the amount of matter that something has, while matter and gravitational pull determine weight. Weight can change depending on where you are in the universe, but the amount of matter we have doesn't (unless matter is lost, such as from dieting).

I ask students to give me some examples of objects in the room that are made of matter.

I follow that conversation up with a question: "Does water have mass and take up space?"

Students generally agree that it is matter because it is "heavy" and it takes up space in the bucket. I use this as a good transition point for the lesson by saying that today we are going to investigate the curious characteristics of water.

This is a good pausing point to remind students to return to their KWL and give them some time to update it.


20 minutes

Now I frame our first investigation: "Does water hold together or fall apart easily?"

Explore Activity 1:

To address the question, students create mini-experiments/tests with their group (4-5 students) using wax paper (or a laminated piece of paper), droppers, and water.  I guide students by asking questions to get them going.  For example, if groups are struggling to get started, I might ask what could they do to see if water breaks apart easily.  

I instruct students to write the following in their science notebooks:

1) Draw a picture/describe in words each test that you performed

2) Record the results from each test

3) Reflect on what you learned from that experiment and predict what might be happening that is causing your results.

We then share our results from our experiments and predictions (2 minutes).

Common result:

- Water sticks together and is difficult to separate.

Ask, "Anyone updating their KWL? What's changing? What are you adding?"  (It's important to explicitly return to a tool introduced at the start as something they need to keep updating. It's a lot for students to remember in the excitement of the investigation.)

Explore (Part 2)

5 minutes

Now that students have performed their own investigation, I run the following demonstration for the class. I project the demonstration on the board using a document camera and LCD projector. Alternatively, you could have one cup of water at each desk for each group to observe more closely. Remind them that they'll need to be looking for new information, answers for any questions remaining, or revisions to their thinking.

The purpose of the demonstration is to elicit understanding that water molecules are in motion.


• Tall clear plastic cup

• Water (room temperature)

• White sheet of paper

• Food coloring (red, blue, or green)


1. Have students make predictions about what will happen when food coloring is added to room temperature water.  Add water to the cup until it is about ¾ filled.

2. Ask students to watch closely as you add one or two drops of food coloring to the water. Do not stir. Instead, allow the color to slowly mix into the water on its own.

3. Hold the cup up with a sheet of white paper behind it so it is easier for students to see the color moving and mixing in the water.

Expected results:

The drops of food coloring will slowly move and mix into the water. Eventually all the water in the cup will be evenly colored.


10 minutes

Now that students have a general sense of what happens when water is pulled apart or pushed together, it is important to give them the opportunity to explain this abstract phenomenon. You can either project the following animations on the board or have groups clean up their water and then give out laptops/tablets.

Again, I want this lesson to be more student-centered, so I am not going to stand in front of the room and lecture to my students. They will access the multimedia section of the American Chemical Society's Molecules in Motion and take notes on what they're learning from the three sections found at the link.  

Students are working with a partner. It is important to give them a goal, and that is to work towards establishing cause and effect relationships that help explain the phenomena that they've observed in class. Here's where the KWL could end naturally, as students now move into using that information in their partner talk, and in their notes. For some students, the KWL format might continue to be a good structure because it helps them to identify what information they are looking for.

Students record their observations and notes in their science notebooks. Encourage students to draw pictures and add written descriptions. 


20 minutes

The extend activity gives students an avenue to reapply and deepen their understanding of the basic properties of water.  Students are asked to either drag a droplet of water around a race track or drag water from multiple locations around a circle to the center.

The purpose of these activities is for students to experience the difficulty of separating and the ease of combining water molecules.  Students then reflect on their experiences to explain why water acts the way it does.  At this point, they are expected to use a molecular explanation.

Check for Understanding: Ask students to explain why the water molecules are acting the way they are.  


Write a reflection about what you learned about water today and how it may have differed from what you originally thought at the beginning of class today.