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11.2: Lesson 11.1 Radioactivity

Difficulty Level: At Grade Created by: CK-12
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Key Concept

Radioactivity is the ability of an atom to emit radiation from the nucleus. Many elements have one or more radioactive isotopes, and elements with more than 83 protons have only radioactive isotopes. Harmless background radiation comes from many sources such as cosmic rays. Radon and some other natural sources of radiation are harmful. Radiation has several uses, including uses in medicine.


  • SCI.CA.8.PS.7.b
  • NSES.5-8.F.1.7
  • AAAS.6-8.1.A.2; AAAS.6-8.6.E.6

Lesson Objectives

  • Explain radioactivity and how it was discovered.
  • Describe sources, dangers, and uses of radiation.

Lesson Vocabulary

  • radiation: particles and/or energy emitted by the nucleus of a radioisotope or an accelerating particle
  • radioactivity: ability of an atom to emit charged particles and energy from the nucleus
  • radioisotope: radioactive isotope, or isotope that emits radiation from its nucleus

Teaching Strategies

Introducing the Lesson

Before students delve into nuclear reactions in this chapter, help refresh their knowledge of subatomic particles and isotopes. Play the well-done music video “Parts of an Atom Song” at the URL below. It was created by a sixth-grade science teacher for his students, using catchy music by the popular band Maroon 5.

Using Visuals

Have students use the periodic table in the FlexBook® lesson to identify all of the radioactive elements (atomic numbers 84–118) as well as the naturally occurring radioactive elements (atomic numbers 84–92). Point out that many elements with lower atomic numbers also have radioactive isotopes. Ask each student to select a number from 1 to 83 and find the element with that atomic number in the periodic table. Then have them suggest a possible radioactive isotope for that element. They can see if they are correct with an interactive elements site such as this one: http://www.webelements.com/.

Differentiated Instruction

After students read the opening paragraph of the FlexBook® chapter, ask them to make a KWL chart to guide their reading of the first lesson. A sample chart has been started below (see Table below). They should fill in the Know and Want to Know columns before they read the lesson and the Learned column as they read or complete the lesson.

Know Want to Know Learned
Example: Elements cannot change to other elements in chemical reactions. Example: How can some elements change to other elements? Example: Some elements can change to other elements when their nuclei give off particles and energy.


Suggest to students that they learn more about the research on radioactivity of Antoine Henri Becquerel and the Curies. They can start with the URLs below. Ask them to create a PowerPoint presentation to share what they learn with the rest of the class.

Science Inquiry

Have students do the “Personal Radiation” activity (pages 36–39) at the following URL. In the activity, students can calculate the amount of natural radiation to which they are exposed and then formulate a hypothesis as to whether they need to modify their environment or behavior.

Common Misconceptions

Misconceptions about radioactivity and radiation are common. The following URL identifies several of them and explains why they are incorrect. For each misconception, the Web site also offers detailed tutorials, simulations, or other interactive media that you and your students can access.

Reinforce and Review

Lesson Worksheets

Copy and distribute the lesson worksheets in the CK-12 Physical Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.

Lesson Review Questions

Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.

Lesson Quiz

Check students’ mastery of the lesson with Lesson 11.1 Quiz in CK-12 Physical Science for Middle School Quizzes and Tests.

Points to Consider

In this lesson, you read that unstable nuclei emit particles and energy.

  • What type of particles do you think unstable nuclei emit?
  • What form of energy do you think these nuclei give off?

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Date Created:
Nov 11, 2013
Last Modified:
Jul 31, 2016
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