Prepared by Columbia University NSEC for non-profit use by students and teachers associated with Nanoday, April 17, 2004

Transcription

1 NOTES TO THE TEACHER: The model lesson plan below has been developed to introduce students to the field of Nanotechnology in advance of Nano-Day. The design of the plan was selected by a committee of Barnard students and representative Science educators. Please feel free to vary the presentation to suit the needs of your students and to address their levels of knowledge in Chemistry and Physical Science. OBJECTIVES: 1) To define the prefix NANO as it applies to the real world and the scientific field of NANOTECHNOLOGY 2) To review the structure of carbon and its three allotropes, and to relate these to the Science of NANOTECHNOLOGY 3) To begin a discussion of the practical real-world applications of NANOSCIENCE THE LESSON I. SCENARIO (suggested context) 1. Introduce the lesson by explaining that it is being presented in preparation for Nano-Day at CUNY. Explain that the presentations the students will participate in on Nano-Day will introduce them to the field of Nanoscience. Then ask students to speculate on the meaning of Nanoscience and Nanotechnology, and on the ways in which it is likely to affect Science research. List students answers on a sideboard for further reference. 2. Divide class into groups of four and distribute copies of the accompanying BRIEF, THE DOCTOR S DISAPPEARANCE (student edition). Review the scenario describing the disappearance of the Doctor. Characterize the Doctor as a scientist without whom current research into Nanoscience probably could not continue. Then elicit the following problem: Where is the Doctor? As the aim of the lesson. 3. Use the accompanying Teacher s Edition to guide the rest of the lesson. a) allow student groups time to discuss each of the discussion points included in the brief. b) Discuss each point by reviewing appropriate answers provided in teachers guide. c) Wrap up the lesson by tying together the clues: pencil lead, soccer ball, large diamond. Include in the wrap-up the important information about nanoscience learned thus far. 1

2 II. Alternative Approach and/or Enrichment Refer to movie Honey I Shrunk the Kids and/or Incredible Voyage and discuss the significance of the events in this (these) movie(s) in terms of nanoscience. Have students speculate on the idea that if this were real, what changes would have had to occur in order for the kids and/or the scientists to be reduced to microscopic size and remain whole and functional. This could lead to an interesting discussion about arrangements and rearrangements of molecules to reduce the size of both animate and inanimate objects. It would also serve as an excellent way of introducing a discussion as to how nanoscience and nanotechnology can be applied to research and medicine. It might be a good idea to remind your students that ROCKET TO THE MOON was once a Science Fiction movie way before their time. If you use this approach, the accompanying brief would be an excellent source of reference from which to obtain examples and explanations of nanoscience and nanotechnology. 2

3 Brief: The Doctor s Disappearance FIELD OPERATIVE: INVESTIGATIVE UNIT: UNIT CHAIR: [STUDENT S NAME] [SCIENCE CLASS]] [TEACHER S NAME] We are part of IBSI, the International Bureau of Scientific Investigation, an elite organization of scientists and field operatives. Your teacher is the Chair of your IBSI Unit and you have been selected for this project. Your first mission is a rather unusual case Our client is so famous that she is often known only as the Doctor. Considered the Einstein of the 21 st Century, she has won Nobel Prizes in Chemistry, Physics, and Biology. One week ago, her colleagues at the University of Manhattan noted her absence. Finding no evidence of foul play, her highly specialized nanoscience research team reported her disappearance to IBSI. We have minimal leads. Our Investigative Branch found on the Doctor s office desk three objects: a pencil, a soccer ball, and most unusually a diamond the size of a golf ball. Our mission, should you choose to accept it, is find the doctor and the reasons for her disappearance and hopefully recover this world-class researcher. In order to do this, we must stand in her shoes. We have to think about our world on the scale of the nanometer. If you ll turn to page 2 of your brief, we ll begin our investigation. 3

4 Brush-Up on the Facts Scale You are waiting for the subway. One, two, three... ten cars zoom past. As you slip into one of them, you sit down and realize that you take up only 1/100 of the space in the car. In comparison to the ten subway cars that just whizzed passed you, you are only 1/1000 their size. This is how the Doctor sees the word through tiny fractions. Though the objects of her research are far smaller than what we can see with the naked eye, they are powerful; just as you are, even though you are only 1/1000 the size of the train. Scientists like the doctor, use the metric system to describe sizes of mass (gram), volume (liter), and length (meter). Some prefixes of scale in science are centi (1/100 or 10-2 ), milli (1/1000 or 10-3 ), micro (1/1,000,000, one part in a million, or 10-6 ), and nanometers (1/1,000,000,000, one part in a billion, or 10-9 ). We can physically comprehend the length of a meter (m) by comparison with our everyday surroundings. Discussion Point 1: Estimate the length of a New York City Block in meters:. ANSWER: 81.3m. A kilometer is 1000 meters, about 12.3 city blocks. We can also visualize a centimeter (cm). Discussion Point 2: Draw a line whose length is 1cm:. TEACHER DRAWS ONE METER ON THE BOARD, THEN A CENTIMETER POINTING OUT THE RELATIVE SMALLNESS OF THE CENTIMETER. How many centimeters are there in one city block? ANSWER: 8130 cm or 8.13 x 10 3 cm. In comparison to the length of a city block, or a subway car, a centimeter is already a very small unit of measurement. Now we will move to a less familiar scale in our world. A millimeter is 1/1000 of meter, and 1/10 of a centimeter as shown in Figure 1 below. Figure 1: Pin. The head of a pin is 1-2mm This image, called an electron micrograph, was taken using an electron microscope. 4

5 Discussion Point 3: Can you think of four objects that can only be seen using a microscope? Four objects that are too small for us to see with the naked eye? STUDENTS THINK OF 4 EXAMPLES, MAY INCLUDE: a cell, organelles, microorganisms, a virus, atoms, molecules, components of gases in the atmosphere (you can feel the wind, but you cannot see it ) This is the beginning of our visual investigation of scale. Please look at The Scale of Things Nanometers and More, Figure 2 below, for discussion. Figure 2: The Scale of Things Nanometers and More Discussion Point 4: How many meters long is one ant that measures 5 mm? ANSWER: m or 5 x 10-3 m. Discussion Point 5: In Figure 2, on the bottom right there is a round shape. Look at the picture labeled carbon buckyball (1 nm (nanometer) in diameter) What does the shape of the buckyball remind you of? BEST ANSWER: a soccer ball. (NEXT CARBON AND ITS ALLOTROPES) 5

6 Discussion Point 6: Let s think about the three items left on the Doctor s desk. a pencil a soccer ball a diamond the size of a golf ball What do they have in common? ANSWER: the pencil and diamond both contain carbon; the soccer ball has the shape of the carbon image in the Nanoworld graphic. Discussion Point 7: The lead in pencils is made of a form of carbon called graphite. Graphite is shiny gray and is a purified form of coal. Diamonds are also made of carbon, but look very different. They are colorless solids with sharp edges. The different forms of an element (like carbon) are called allotropes. These properties discussed so far are differences in how the allotropes, graphite and diamond look. How do these allotropes behave? ANSWER: student answers should talk about (or be guided toward) the differences in the properties of the materials Diamonds are robust enough to use in everyday jewelry and can cut glass Graphite is very soft and can leave a black mark on paper without cutting the paper Discussion Point 8: Can you think of other examples of objects composed of the same element or material but that have different structures? ANSWER 1: wood and saw dust. They are made up of the same element but their texture and structure are different. One is a hard solid and the other is also a solid but is soft and fine. If the strong connections that hold the wood (cellulose) together are destroyed, the strength is gone. ANSWER 2: Plastic bags vs. milk jugs. The plastic bag has a low-density polyethylene (LDPE) structure and the plastic in a milk jug is composed of high-density polyethylene (HDPE). The low-density polyethylene structure is more flexible than the high density. On the bottom of most plastic containers, you are likely to see a recycle symbol containing a number. These numbers indicate the kind of polymer from which the container is made and indicate their composition and suitability for recycling. The gallon of milk is a number two and the ziplock bag number four. The arrangement of atoms is a very powerful factor in determining not only the appearance of a material, but also the strength. Since the strength of diamond and graphite are very different, we should not be surprised to find that their structures on the nanometer scale are also quite distinct. 6

7 Discussion Point 9: The lead of a pencil is a form of carbon called graphite. When coal is dug up out of the ground it is a very impure form of graphite. How could a single type of building block, the carbon atom, be connected so that it binds strongly in two dimensions and the graphite holds together in the pencil, but is weakly bound in the third dimension so that layers of graphite can rub off on paper? ANSWER: [ The atoms are bound strongly to each other in planes, but only weakly bound in the third dimension. Students can think of this like layers of pastry, stacks of paper, or plastic that is thin but resistant to tearing. ] At the molecular level, the carbon atoms in graphite are arranged in sheet-like structures that are able to slide over each other. Graphite s structure is therefore not as rigid as that of the diamond and is a much softer material. Discussion Point 10: If you only had one type of building block, namely a carbon atom, how would you arrange the atoms in space so that they were equally strongly connected in all three dimensions? ANSWER: [ The atoms bind to each other equally in three dimensions so no direction is different from any other. ] At the molecular level the carbon atoms in diamond are arranged in a particular structure called a crystal lattice which gives it its distinct shape. Each carbon atom in diamond is bonded to three other carbon atoms, giving it a rigid structure called tetrahedron. This is why diamonds are forever. Diamond s structure makes it a very hard solid, and why diamonds can be used industrially to cut other materials. They are strong stuff! This is why you are able to write with graphite and not diamond! They are two compounds solely comprised of carbon, 7

8 but it is the arrangement of the carbon atoms in these compounds and their atomic structure that make these elements so different. Discussion Point 11: Let s return to the Buckyball picture in Figure 2. This buckyball is a third allotrope of carbon, discovered in It is completely different from graphite and diamond. If we took the shape of a soccer ball, and place one atom at each corner, how many atoms will there be? ANSWER: 60 The allotrope C60 gets its nickname of buckyball because its icosahedral shape (20 faces) was studied by the architect Buckminster Fuller. C 60 and other related molecules are also called fullerenes. Discussion Point 12: What are the shapes on the surface of a soccer ball made by the intersections of the lines? ANSWER: pentagons and hexagons Discussion Point 13: What might you expect for the physical properties of a buckyball in contrast to diamond and graphite? ANSWER: [student answers and discussion should be guided toward the lack of infinite structure and toward the discrete molecules of C 60 ] Now we have an idea why there were three objects on the Doctor s desk: each one corresponds to an allotrope of carbon: graphite, diamond, and the buckyball (C 60 ). You find a paper on the Doctor s desk with a post-it that reads: Discuss with Al O. Above the desk you see a list of the members of the Doctor s research group Moe Mentum Al O Trope Polly Mer Mer Curie Maybe one of them will have some information? Lesson #2: Interviews with the Doctor s Colleagues 8