Engage (5 – 10 minutes):
Stand at the front of the classroom and spray air freshener into the air. Have students describe what they see to a partner. (The droplets go into the air, begin falling, and then disappear. Some students may say that the air freshener falls to the floor. Rather than challenging this idea, continue with the demonstration so students can figure out what happens for themselves.)
Ask students to raise their hands when they smell the air freshener. (Students at the front of the classroom will smell it first, and then others will begin to sense it as the air freshener diffuses throughout the room.) Have partners discuss why they think everyone did not smell the air freshener at the same time and how they were able to smell it at all since you did not spray it directly on them. How did the air freshener reach the back of the room without being seen?
Shake the can of air freshener and ask “Is the air freshener a liquid or a gas?” What causes the liquid to change form? Is it still the same substance when it changes from a liquid to a gas? How do you know?
Tell students they will explore different types of matter to find evidence that it is there, even if they cannot see it, because it is made of particles too small to be seen. Then students will prove that matter is made of particles too small to be seen using evidence from their investigations.
Explore (10 - 15 minutes):
Divide students into groups of four and distribute materials to each group. Have each group measure 1 cup warm water in a 2-cup measuring cup (or 100 ml warm water in a graduated cylinder). Drop the solid objects in the water and observe what happens (the water level rises). Ask students why this happens (the objects displace the water). Remove the objects from the water, making sure that no water is spilled or refilling the cup/graduated cylinder to the previous level.
Tell students that they will now mix ¼ cup sugar into the cup of water. Have them predict what will happen to the water level. Distribute one color of sticky notes. Have students write their names on the notes and use them to make a class prediction graph on chart paper (see sample graph in attachment section). Students will predict whether they think the water level will decrease, stay the same, increase slightly, or increase by ¼ cup. Have students discuss the reasoning behind their predictions.
Have students dissolve ¼ cup sugar into the cup of water and observe what happens to the water level. Give students a second color of sticky note for them to write their names on and post on the class graph showing what they observed. Have students discuss the following questions in their small groups:
- Why didn’t the water level rise by ¼ cup when we added ¼ cup sugar?
- Where did the sugar go? How is that possible?
Explain (15 -20 minutes):
View and discuss slideshow about particles.
Read the explanation of particles on pages 52‐57 in Dr. Art’s Guide to Science. In this explanation, the author compares the particles of solids, liquids, and gasses to dance partners at a party. The same number of dancers (particles) are present at each point, but the size of the dance floor (phase of matter) determines how much the dancers can move and what types of bonds they form. As you read this explanation, demonstrate the three phases of matter by doing a demonstration with ice.
Show students an ice cube and ask what it is made out of (water). Put the ice cube in an electric skillet and begin heating it. Allow it to melt as you read the portion of Dr. Art’s story about liquids. Tell students to observe how the water spreads out once it has melted. Continue reading about gasses as the water begins to boil and change to water vapor. Students will observe steam rising, but then the water seems to disappear. Where has the water gone? How can we prove that the water is still in the air? (Hold your hand or the lid of the skillet over the water and feel or see the vapor condense back into water.) Remind students that even though the water particles may spread out so much that they are no longer visible, they are still present.
Elaborate (25 - 30 minutes):
Students will use air to complete an engineering design challenge to prove that matter is made of particles too small to be seen.
Show students Zoom 1.5-minute video from PBS. In this video, children use air to lift a heavy table. Discuss how this proves that matter is made of particles too small to be seen. (Even though we cannot see air in the plastic bags, it must be there to be able to lift the table.)
Tell students they will plan and conduct investigations that also prove the existence of tiny invisible particles. Provide access to the following materials: balloons, straws, tape, paper, cardboard, empty water bottles, and plastic bags. Students may work individually or in pairs to create something with the materials that shows the existence of air. Their investigations may be as simple as releasing an inflated balloon to see it zip across the room as air is released, or as complex as a cardboard car powered by air. Have students use the planning guide from the attachments section (“Proving Matter is Made of Tiny Particles Using the Engineering Design Process”) to plan, implement, and explain their investigations. Students must construct a device consisting of at least two parts that can be used to demonstrate the existence of particles too small to be seen, present their devices to the class, and explain how this device proves these invisible particles exist.