Unit #1

Activity 3
Have You Seen an Atom Lately?

Activity Overview

Everything is made of atoms.

In this activity students investigate the question: "What is matter and what is it made of?" Students debate the merits of two opposing views of matter and then conduct two experiments to provide evidence for one or the other view. Students then conduct two experiments:

1. Observing the spreading of a drop of oil on water.
2. Mixing a measured amount of alcohol and water.

The results of these experiments will be used to support one of the views of matter. Then a demo is performed in which is an analogy of the second experiment by combining stones and sand.

Finally, students view some images created with a Scanning Tunneling Microscopes (STM) that represent atom locations.

Learning Objectives

Students will:

• Utilize the idea of atoms to explain the results of several experiments.
• Classify things as matter or non-mater.
• Analyze two opposing views of matter.

Conceptual Prologue

Macro-Micro Connection

To understand what happens to the air in the hot air balloon, students need to understand what air is on an atomic scale. While students can be told that "everything is made of atoms", research shows that they don't understand it properly. This activity exposes them to a couple of experiments that are best explained if everything is made of tiny pieces (atoms*) with space in between.

*Actually, the "tiny pieces" of water and alcohol are molecules, not individual atoms. To keep things simple we will only talk about atoms during this unit. The behavior of atoms and molecules is not significantly different at this level.

Science Concepts

There are only two possibilities for the underlying structure of matter: either there is a smallest piece of something (the particle theory of matter), or you can divide a thing in half forever, never reaching a smallest piece that can’t be divided (the continuous theory of matter).

After many years and experiments there is good evidence that all matter consists of atoms and molecules [tightly bonded groups of atoms]. The smallest part of an element is a single atom and the smallest part of a compound [more than one kind of element bonded together] is a molecule. The molecule can be broken down into single atoms, but those separate atoms are no longer a piece of the compound because the definition of a compound requires bonded atoms. For simplicity, the term particle used in this activity could refer to either atoms or small molecules. The term atom should not be used until the end of this activity, but should be used exclusively for future activities in Unit 1.

Today we have instruments that can "see" atoms. The scanning tunneling microscope was the first such instrument to give us direct observations of single atoms.

Naive Conceptions

• Matter is continuous.

Matter is not continuous. Matter is made of atoms and/or molecules which are clusters of atoms. There is empty space between molecules. Even if students believe that atoms exist, they often think a substance has atoms in it, with some unspecified substance between the atoms. Instead, they should understand that the atoms and molecules are the substance with complete nothingness between those atoms and molecules. The idea of completely empty space can be difficult for students to comprehend (particularly because of naive conceptions that matter is continuous).

• Everything is matter.

Only substances that have mass are considered matter. Often students think heat, light, and other intangible substances are also matter.

Activity Design and Execution

Major Science Concepts:	• atomic theory of matter
Assumed Previous Knowledge:	• None
Time:	• Approximately 75 minutes
Materials:	For the first experiment each group will need: • A cafeteria tray. • Some vegetable oil or oleic acid. • Some talcum powder. • An eyedropper. For the second experiment each group will need: • A small test tube. • Water. • Rubbing Alcohol. • 2 eye droppers; one for the water and one for the alcohol For the demonstration: • A large cylinder half filled with stones. • A large cylinder half filled with sand.
Advanced Preparation: (if any)	• none

Investigative Question: What is matter and of what is it made?

1. Make a list on the board of things that are matter and those that are non-matter. Ask students to describe how you know something is matter. [You should eventually get to the idea that matter has mass and you can weigh it on a balance.]
2. Explain to the students the two opposing views of matter:
   

   - The continuous theory of matter: any substance can be cut in half forever, never reaching a smallest piece.
   or
   - The particulate theory of matter: at some point when dividing a substance in half you eventually reach the smallest piece of something that can't be divided.

3. Hand out the lab instructions/questions for Oil Spreading on Water.
4. Discuss the questions on this lab with the whole class. [After placing a drop of oil on a tray of water, students will have noticed that the oil only spreads so far. This is evidence that the substance can’t be divided into infinitely small pieces, because if this were true, there would be no limit to how thin the oil could get or how far it could spread.]
5. Hand out the lab instructions/questions for Mixing Alcohol and Water.
6. Discuss the questions on this lab with the whole class. [After mixing alcohol and water, students observe that the volume of the mixture is less than the sum of the two individual volumes. If water and alcohol are made of particles there should be some space between the particles. When mixed together, one particle and occupy some of that in between space of the other, allowing for the volume of the mixture to be less than the sum of the two separate volumes.]
7. To show students why the particle theory of matter can help to explain why a mixture of alcohol and water has a smaller volume than the two separate substances, do the following demonstration:
   

   - Show the students a large cylinder filled with stones to the top and another one that has some sand in it.
   - Add sand to show there is actually more room in the cylinder, so that the volume of stones and volume of sand are less than the two mixed together.

8. Discuss how this demonstration might be used as an analogy to help explain the previous experiment with alcohol and water.
9. Explain the the particles all substances are made of are called atoms, similar to the atom they saw in the previous activity when they zoomed down to an extremely high magnification using the ZoomIt software.
10. Explain to students that we have a special kind of instrument which can’t “see” atoms directly but can tell where they are and give us a image of their location. Be sure to explain that single atoms don’t have the colors displayed in the images and that a bump represents and atom.
11. Have students use an internet browser to visit the URLs below. Tell them to read the first one and then go to the others and click around to view various images:
    

    http://www.howstuffworks.com/atom9.htm

    http://eaps4.iap.tuwien.ac.at/www/surface/STM_Gallery/reconstructions.html
    
    http://www.almaden.ibm.com/vis/stm/gallery.html

Assessment

Have students place the lab sheets into their notebooks.

Have students write several things in their notebooks:

1. Ask them to describe how you know when something is matter or not matter and give an example of each.
2. Ask them to describe why the two experiments support the particulate theory of matter.
3. Ask them what they would expect to observe if the oil were made of even smaller pieces. Would it spread out more, less, or the same? Why?
4. Ask them to describe what the air inside the balloon looks like if they could look at it with a magnifying glass that was powerful enough to see atoms.