ATOMIC DIMENSIONS. Background for Teachers KEY CONCEPT

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1 ATOMIC DIMENSIONS KEY CONCEPT The volume of an atom is mainly empty space. Relative distances within an atom are difficult to visualize using drawings because they are similar to distances found in our solar system. SKILLS... measuring, comparing, and concluding TIME minutes AUDIENCE...grades 4-7 NATIONAL SCIENCE CONTENT STANDARDS.. U-1. Systems, order, organization U-2. Evidence, models, and explanations U-3. Change, constancy, measurement A-1. Abilities to do scientific inquiry Background for Teachers The dimensions within an atom are difficult to visualize using drawings or visual techniques due to the great differences in size and distance of the various parts. Most of us have seen representations of atoms showing the nucleus in the center and the electrons depicted around the outside in some manner. The picture below, for instance, shows the center and surrounding electrons, but in reality is a very distorted model of an atom. Part of the reason is because electrons have both particle and wave character and cannot be thought of as a discrete piece of matter. Another reason is the shear scale of the representation. For instance, if protons and neutrons in the nucleus were a centimeter in diameter, then electrons would be smaller than the diameter of a hair. Also with this scale, the diameter of the atom would be greater than the length of 30 football fields! If we put this scale into perspective by using powers of ten, we would find that the nucleus of an atom would be 10,000 times as large as an electron. But the distance of the electrons from the nucleus would make the size of the atom approximately 10,000 times the size of the nucleus. Calculations have shown that % of the volume of an atom is just empty space! In this activity, students will produce a model based upon these relationships.

2 The Activity: Atomic Dimensions MATERIALS (for teacher) Long hallway; gym or playground Picture of an atom (from a text book or from this activity) Cut out an Atomic Dimension Ruler for each group (per group: best to have at least 10 groups or have each group make 2 kilonucs. [There should be at least 10 kilonucs (KN) to complete the activity) Atomic dimension ruler tape rolled register tape Teacher s Procedure 1. Show students a picture of an atom from a chemistry book or use the one from this activity. Have them think about the following questions: a. In this picture, how close do they think the center of the atom is to its outside? b. What do they think is inside the atom between the center and its outside? 2. Inform them that sometimes models do not do good jobs of representing the actual distances of parts within the object. They will be constructing a model of an atom today. 3. Have students begin the activity through step 3, then give them their cutout ruler. 4. After students have measured their 1000 nuclei, have them bring the cut length of register tape to you. We ll call the length of 1000 nuclei a kilonuc or KN. 5. Gather together all of the KNs (each one now represents 1000 nuclei) and take the students to a hallway or other large area. 6. Have the students place their KNs end to end until they have measured out 10,000 nuclei. This will represent the diameter of an atom. Place a piece of tape on the floor. Find the center of this line and mark the nucleus at this point. Have the students look at the size of the nucleus of this atom (inked dot), and the size of the diameter of the atom itself. 7. Emphasize that the inside of the atom is much like outer space. There is nothing but space between the nucleus and the electrons. 8. Ask them to write a paragraph about their impressions of the atomic model they have made. 2

3 Atomic Dimensions Student Procedure and Data Sheet 1. Below you will find the beginnings of an Atomic Dimension Ruler (AD Ruler). The dot represents the size of the nucleus of an atom. Remember that the nucleus is the center of an atom. 2. There are 10 dots between the first 2 lines. How many nuclei does this represent? 3. There are 5 equal spaces on your AD Ruler, how many dots do you have on the AD Ruler? How many nuclei does this represent? 4. Your teacher will now give you a cut-out version of your AD Ruler. You will use that ruler for the rest of the activity. THE AD Ruler 5. Place your AD Ruler on a piece of register tape, marking the beginning and the end of the ruler. Remember that this represents 50 nuclei. 6. Pick up the AD Ruler and lay it down again right next to your second line. Mark the other end of the ruler as you did before. You now have the length of 2 of your AD Rulers. How many nuclei does this represent? 7. Fold the register tape over at the line that represents the length of 2 of your AD Rulers. Use this length to fold over the tape until you have a length to represent 1000 nuclei. Cut the tape at that point. Explain how you did this below. When you are finished, take your length of tape (1 kilonuc or KN) to your teacher. 3

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