Lesson 1 Plan

Atoms and Radiation

Purpose:

The purpose of this introductory lesson is to acquaint students with essential concepts about atoms and molecules, and to present the basics of radiation and radioactivity.

Concepts:

1. There are 92 naturally occurring chemical elements, some of which are radioactive.
   
   
2. An atom is the smallest part of a chemical element that has all the chemical properties of that particular element.
   
   
3. Each atom has a nucleus that determines its chemical properties, based on the number of protons in the nucleus.
   
   
4. Some atoms have more than one isotope — i.e., isotopes of a given element are atoms with varying numbers of neutrons but the same number of protons in their nuclei.
   
   
5. The nucleus of a radioactive atom (called a radioisotope or radionuclide) spontaneously emits an electrically charged particle, thus changing the atom into a different one. Sometimes when a radioactive atom emits an electrically charged particle, it also emits a gamma ray. The energy released from a radionuclide, whether in the form of a particle or a ray, is called ionizing radiation.
   
   
6. Radiation is important, useful, and occurs everywhere.
   
   
7. Ionizing radiation is unavoidable, but too much can have health consequences.

Duration of Lesson:

One or two 50-minute class periods

Objectives:

After participating in this lesson, students will be able to

1. define atom, atomic number, atomic weight, isotopes, and radiation;
   
   
2. name the parts of an atom;
   
   
3. discuss the difference between radiation and ionizing radiation;
   
   
4. discuss everyday applications and uses of radiation and radioactive materials;
   
   
5. read and interpret the Periodic Table (optional).

Skills:

Analyzing, discussing, expressing opinions, interpreting/using charts (optional), reading comprehension

Vocabulary:

Atom, atomic number, atomic weight, electron, ionizing radiation, isotope, molecule, neutron, nucleus, nuclide, proton, radiation

Materials:

Reading Lesson: “Atoms and Radiation”

Student Activity Sheets:

“The Chemical Elements and Their Symbols”

“The Periodic Table”

“Atoms and Molecules”

“Chemical Element Worktable: Identifying Elements”

“Chemical Element Worktable: Identifying Isotopes”

Answer Key for “Atoms and Molecules”

Answer Key for “Chemical Element Worktable: Identifying Elements”

Answer Key for “Chemical Element Worktable: Identifying Isotopes”

Suggested Procedure:

1. Assign the reading lesson entitled “Atoms and Radiation.”
   
   Explain to students that the reading lesson covers essential concepts about atoms, nuclides, and molecules. The lesson also introduces basic facts about radiation.
   
   Depending on the students’ knowledge of atoms, you may wish to discuss why the number of naturally occurring elements is smaller than the number of elements on the periodic table. Or you may wish to save this discussion for a later lesson in this unit.
   
   (We know for certain that 92 elements exist in nature. Physical evidence indicates that at least two other elements are present from time to time because they are part of the decay chains of some naturally occurring elements. Students may become confused because the periodic table indicates 103 elements. The reason for the discrepancy is that scientists have produced small amounts of very heavy elements in the laboratory that do not normally exist in nature.)
   
   
2. Engage students in a class discussion upon completion of the reading lesson.
   
   
3. Assign the following for homework:
   
   (a) Have students write a paragraph about the difference between radiation and radioactivity.
   
   (Students should be aware that radiation is energy that moves through space in the form of waves or particles. Radioactivity is the property of certain chemical elements to spontaneously emit ionizing radiation, both as charged or nuetral particles and as gamma or xrays.)
   
   (b) Ask students to list as many everyday uses of radiation as they can. They may look these up in reference books or do a search on the Internet. They may want to ask friends and family members to help them.
   
   (Answers will vary. However, you should be looking for such responses as the following: Radioactive materials have many different uses. They are used in medicine, scientific research, and industry; they help generate about 20 percent of America’s electricity and in some countries a much higher percentage. Doctors have learned many different ways to use radioactive materials in the diagnosis and treatment of various diseases, including cancer. We also use radiation to “label” and study matter. When substances are “labeled” with radioactive elements, we can trace the path these substances take through living plants or animals. This helps us learn important facts about how to better care for the plants and animals and ourselves. Industry uses radiography to check the quality of many aspects of different products, such as the strength of metals and welds. In addition, radioactive elements are used in such common items as thickness gauges, rifle and bow sights, and household smoke detectors. Radiation is also used for analyzing evidence from the scene of a crime; for preserving foods; for sterilizing surgical and medical instruments, thereby protecting patients from getting infections; and for dating art, antiques, and many ancient remains.)
   
   
4. Have students read the background notes entitled “The Chemical Elements, Isotopes, and the Periodic Table.” Then have them practice using the alphabetical chart “The Chemical Elements and Their Symbols” in conjunction with The Periodic Table. (Students need to be aware that some of the elements have symbols that won’t be intuitive to them; thus, the importance of the alphabetical list, until they have memorized all the symbols.) After the students learn how to use the chart and table together, have them do any or all of the activities: “Atoms and Molecules,” “Chemical Element Worktable: Identifying Elements,” and “Chemical Element Worktable: Identifying Isotopes.”
   

For Class Discussion:

1. If atoms are so small that we can’t see them, how do we know they really exist?
   
   (Scientists learn about atoms through indirect observation. They study those properties or effects of atoms that can be measured in some way. We study other phenomena the same way. For example, we can’t see the wind, but we can see it blow leaves about, and therefore we know it exists. We know its properties and its effects. As another example, we all experience gravity, but we can’t see or hear or touch it. And unless we’ve personally been in outer space, or in an astronaut training program, we’ve never personally experienced the lack of gravity. But we learn about gravity itself by studying its properties and effects.)
   
   
2. If an atom is considered the smallest unit of matter, how can we say that atoms are made of smaller particles such as protons, electrons, and neutrons?
   
   (The atom is the smallest unit of matter that retains all of the chemical characteristics of a particular element. Electrons, protons, and neutrons are fundamental particles that make up the atoms of all elements.)
   
   
3. Why are protons used to identify elements?
   
   (The number of protons in an atom is used to identify the element because all isotopes, or variant atoms, of an element have the same number of protons.)
   
   
4. What is the difference between an atom and a molecule?
   
   (A molecule can be a combination of several atoms of the same element or of different elements. For example, a molecule of water is made of two hydrogen atoms combined with one oxygen atom: H2O. A molecule is always made of atoms; atoms are not made of molecules.)
   
   
5. How do isotopes differ from one another?
   
   (Isotopes of a specific element differ from one another in the number of neutrons in their nuclei. They have the same number of protons in their nuclei; therefore, they have the same chemical properties but not the same atomic weight. They are all atoms of the same element.)
   
   
6. Why is the atomic weight sometimes a fraction?
   
   (The atomic weight is the average of the weights of all the isotopes of an element.)
   
   
7. What is a nuclide? What is a radionuclide?
   
   (A nuclide is an atom’s nucleus described in terms of its atomic number [number of protons] and mass; a radiactive [unstable] nuclide is a radionuclide.)
   
   
8. What is the difference between the words “nuclide” and “isotope”?
   
   (The words isotope and nuclide are often used interchangeably in this curriculum and in practice. When referring to neptunium-237, for example, we can call it either a radionuclide or a radioisotope, either would be correct. The difference in the meaning of the term comes in its usage. For example, neptunium-237 is an isotope of neptunium. Neptunium has several isotopes. “Nuclide” would not be appropriate in either of the two previous sentences — since all isotopes of neptunium are radioactive.)

Teacher Evaluation of Student Performance:

Student completion of activities and participation in discussion will indicate level of comprehension.