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6-8 > Physical Science
Grade level: 9-12 Subject: Physical Science Duration: One class period
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Students will understand the following:
1. Radioactivity is the property of some elements or isotopes to spontaneously emit particles of energy by the disintegration of their atomic nuclei.
2. This process is known asradioactive decay.
3. As a sample of radioactive material decays, it becomes stable and nonradioactive.
4. The amount of time it takes for half of a sample of radioactive material to decay into a stable substance is called itshalf-life.

Each student, pair, or group will need the following:
Shoebox with cover
One hundred items that have distinguishable tops and bottoms (e.g., M&Ms or coins)

1. Ask students if they can define the termradioactivity. Make sure they understand that radioactivity is technically defined as the property of some elements or isotopes of spontaneously emitting particles of energy by the disintegration of their atomic nuclei.
2. Go on to explain the following concepts before proceeding with the activity:
  1. The disintegration of the atomic nuclei of radioactive materials is known asradioactive decay.
  2. As a sample of radioactive material decays, it becomes stable and nonradioactive.
  3. The amount of time it takes for half a sample of radioactive material to decay into a stable substance is called itshalf-life.
  4. The half-lives of different radioactive materials can be anywhere from billions of years to a few seconds long.
3. Have your students demonstrate radioactive half-life by using a shoebox containing 100 items. The items should have distinguishable “heads” and “tails,” as do coins or M&Ms (letters on one side, blank on the other).
4. Instruct students, working individually, in pairs, or in small groups, to put their 100 items into the shoebox with the same side facing up.
5. Have students put the cover on the box and shake the box up and down (not sideways) five times.
6. They should then open the lid and remove any of the items that now have the chosen side facing down. (If one item is on top of another, students should move the item on top to an empty space in the box without changing its orientation.)
7. Have students count the number of items remaining in the box and record the results for the first five shakes.
8. Students should repeat the process until no items are left in the box, recording data as they work (number of items remaining after the second five shakes, third five shakes, and so on).
9. Have students graph the data they have recorded, with “number of items remaining” on the vertical axis and “number of five-shake tries” on the horizontal axis.
10. Students can now determine the “half-life” for their items by calculating how many five-shake tries were necessary to remove 50 of the items.
11. Invite students to share their results. Was the number consistent throughout the class? Why, or why not? What factors may have influenced the results? Are similar factors present in measuring the half-life of an element or isotope? Why, or why not?
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Explain radioactivity to younger students in simpler terms. You might simply say that over time radioactive materials, become nonradioactive.
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Discussion Questions

1. Describe the process by which new elements are created in a laboratory. Should such elements be considered “real,” since they do not normally exist in nature and usually decay rapidly after their creation in the lab?
2. Compare and contrast the radioactive elements on the periodic table. What do they have in common with each other in terms of their chemical structure?
3. Brainstorm a list of elements that you encounter in their pure form in your everyday life.
4. Describe the process by which two or more elements combine to form a compound.
5. The element hydrogen is unique in that it really doesn’t belong entirely in any one of the common element groups. What makes hydrogen so special? Speculate about reasons for this chemical quirk.
6. The Curies risked their health to make what turned out to be an important scientific discovery: the element known as radium. Scientists today continue to work hard to create new elements in laboratories all over the world, but they usually take extensive safety precautions, which sometimes slow down the pace of their research. With safety in mind, what kinds of risks should scientists take in their research? Who should determine whether an experiment is genuinely safe?
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You can evaluate students on their data and graphs using the following three-point rubric:
Three points:data clearly and correctly recorded; graphs carefully prepared
Two points:data recorded; graphs prepared
One point:data poorly recorded and graphed
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Everyday Compounds
Water just might be the most common compound on Earth. As almost everyone knows, two atoms of the element hydrogen (H) plus one atom of the element oxygen (O) make one molecule of water (H2O). Many other everyday substances—things found in almost anyone’s kitchen or bathroom—are also nothing more than simple compounds. Ask your students to brainstorm a list of substances found in their homes that they believe are compounds. Their list might include sugar, salt, baking soda, hydrogen peroxide, and ethyl alcohol, among many others. Then ask each student to choose one of these compounds and conduct some basic research to determine which elements it is composed of. Make sure that each student chooses a different compound to generate as wide a variety of topics as possible. When research is complete, have each student prepare a brief presentation for the class on what she or he has discovered. Each presentation should include a detailed sketch of the compound’s elemental structure. Conclude with a discussion about the most common elements contained in the various compounds students presented. What is the significance of the fact that some elements appear in more than one common household compound? Why are some elements so rare, while others appear frequently?

Element Hunters
In part for her discovery of the elements radium and polonium, Marie Curie won the Nobel Prize for chemistry in both 1903 and 1911—no small feat. Discovering new elements today, however, is a much more challenging endeavor. Scientists must go to tremendous lengths in the laboratory to actually create elements, often by bombarding atoms of one element with atoms from another. Have each of your students investigate the discovery or creation of a particular element. Ask students to research the scientists involved in the elements’ discovery or creation, finding information about the scientists’ educational backgrounds, any awards they received for their efforts, the methods and technologies they used, the new knowledge and practical applications that resulted from their projects, and any other discoveries or achievements for which they are noted. When students’ research is complete, ask them to prepare presentations on the “element hunters” they learned about, perhaps using PowerPoint or HyperStudio. When all presentations have been given, lead a class discussion about the discovery and creation of new elements. Is this an important endeavor? What potential benefits does the hunt for new elements offer the human race?

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Suggested Readings

The Periodic Kingdom
P.W. Atkins. Basic Books, 1995.
This book—a journey into the world of the elements with a scientist as tour guide—tells readers the history of the elements and basic chemistry.

Creations of Fire: Chemistry’s Lively History from Alchemy to the Atomic Age
Cathy Cobb and Harold Goldwhite. Plenum Press, 1995.
Cobb and Goldwhite celebrate the history and personalities that have shaped chemistry. Tracing chemical inventions allows the reader to understand how important chemical inventions are to the development of civilizations.

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Centennial of the Discovery of Radioactivity
This Centennial website tells the story of the history of the discovery and discoverers of radioactivity and provides a reference on the nature of radioactivity.

The Particle Adventure
In an online muldimedia presentation you will take a grand tour of the atom, be introduced to the electron, proton and neutron, and then delve deep into the nucleus of the atom to explore parts that most of us never heard about.

Interactive Physics Modules: Matter
This online interactive multimedia tutorial should be your first stop to learn about the basics of atomic structure and how atoms interact to create more complex compounds.

Hydrologic Cycle
Nature has its own way of desalinating ocean water, and it is called the "Hydrologic Cycle." Animations at this website illustrate each step in this cycle that not only removes salt from our natural water reserves, but also removes many contaminates that we eliminate into our environment.

General Information About Pain
Celebrate the 100th anniversary of the discovery of aspirin with this extensive reference for family use on everything you always wanted to know about pain. From ancient Egyptian pain mythology to the most recent research on endorphins at Johns Hopkins University.

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Click on any of the vocabulary words below to hear them pronounced and used in a sentence.

speaker    aspirin
Definition:A white crystalline derivative of salicylic acid used for relief of pain and fever.
Context:As anyone who’s ever had an ache or a fever knows, aspirin has remarkable properties.

speaker    leukemia
Definition:An acute or chronic disease in humans and other warm-blooded animals characterized by an abnormal increase in the number of white blood cells in the tissues and often in the blood.
Context:Both Marie Curie and her daughter died from leukemia caused by their exposure to radioactive elements.

speaker    osmosis
Definition:Movement of a solvent through a semipermeable membrane into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane.
Context:Osmosis is used to purify salt water in desalinization plants.

speaker    radioactivity
Definition:The property possessed by some elements or isotopes of spontaneously emitting energetic particles by the disintegration of their atomic nuclei.
Context:Marie Curie discovered that the mineral pitchblende, which contains radium, was a source of radioactivity.

speaker    radium
Definition:An intensely radioactive brilliant white metallic element that resembles barium chemically, occurs in combination in minute quantities in minerals, emits alpha particles and gamma rays to form radon, and is used chiefly in luminous materials and in the treatment of cancer.
Context:Radium is a highly radioactive metallic element, discovered by Marie Curie, which was used in cancer radiation therapy.

speaker    semipermeable
Definition:Partially but not freely or wholly permitting liquids or gases to pass through.
Context:A semipermeable membrane is important in the filtering of seawater.

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This lesson plan may be used to address the academic standards listed below. These standards are drawn from Content Knowledge: A Compendium of Standards and Benchmarks for K-12 Education: 2nd Edition and have been provided courtesy of theMid-continent Research for Education and Learningin Aurora, Colorado.
Grade level:9-12
Subject area:science
Understands energy types, sources, and conversions, and their relationship to heat and temperature.
Knows that nuclear reactions convert a fraction of the mass of interacting particles into energy (fission involves the splitting of a large nucleus into smaller pieces; fusion is the joining of two nuclei at extremely high temperature and pressure) and release much greater amounts of energy than atomic interactions.

Grade level:6-8, 9-12
Subject area:science
Understands the nature of scientific knowledge.
Benchmark 6-8:
Knows that all scientific ideas are tentative and subject to change and improvement in principle, but for most core ideas in science, there is much experimental and observational confirmation.

Benchmark 9-12:
Understands how scientific knowledge changes and accumulates over time (e.g., all scientific knowledge is subject to change as new evidence becomes available; some scientific ideas are incomplete and opportunity exists in these areas for new advances; theories are continually tested, revised, and occasionally discarded).

Grade level:6-8, 9-12
Subject area:science
Understands the nature of scientific inquiry.
Benchmark 6-8:
Understands the nature of scientific explanations (e.g., emphasis on evidence; use of logically consistent arguments; use of scientific principles, models, and theories; acceptance or displacement based on new scientific evidence).

Benchmark 6-8:
Knows possible outcomes of scientific investigations (e.g., some may result in new ideas and phenomena for study; some may generate new methods or procedures for an investigation; some may result in the development of new technologies to improve the collection of data; some may lead to new investigations).

Benchmark 9-12:
Knows that conceptual principles and knowledge guide scientific inquiries; historical and current scientific knowledge influences the design and interpretation of investigations and the evaluation of proposed explanations made by other scientists.

Benchmark 9-12:
Knows that scientists conduct investigations for a variety of reasons (e.g., to discover new aspects of the natural world, to explain recently observed phenomena, to test the conclusions of prior investigations, to test the predictions of current theories).

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Mary C. Cahill, middle school science coordinator, Potomac School, McLean, Virginia.
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