Summary

In this activity, students will examine the relationship between the stability of an isotope, its half-life, and the make-up of its nucleus.

Grade Level

High School

NGSS Alignment

This activity will help prepare your students to meet the performance expectations in the following standards:

• HS-PS1-8: Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay.
• Scientific and Engineering Practices:
  • Analyzing and Interpreting Data
  • Obtaining, Evaluating, and Communicating Information

Objectives

By the end of this activity, students should be able to:

• Understand the connection between the stability of an isotope and its half-life.
• Describe the relationship between the stability of an isotope and the make-up of its nucleus.

Chemistry Topics

This activity supports students’ understanding of:

• Nuclear Chemistry
• Radioactive Decay
• Half-lives
• Nuclear Stability

Time

Teacher Preparation: 20 minutes
Lesson: 60 minutes

Materials

• Student Handout
• Electronic Device (Tablet, Chromebook, laptop, etc.)

Safety

• No safety precautions need to be observed for this activity.

Teacher Notes

• For this activity, it’s recommended that students work in small groups. They can help each other analyze the data and record it.
• The International Chart of Nuclides was chosen for this activity because it provides an interactive band of stability that encourages students to analyze data and think about what it means in terms of the most stable atoms. It also provides an opportunity for students to identify patterns in the band of stability.
• Before starting the activity, explain to students that a KeV (kiloelectron volt) is a unit of energy, similar to a calorie, which should be familiar.
• Understanding scientific notation is important for this activity. Students will need to be able to interpret scientific notation and convert from standard to scientific notation.
• It would be helpful to prepare students for this activity by first showing an example data table for an isotope from the Nuclides website. To do this:
  • Start with the Live Chart of Nuclides from the Nuclides website.
  • Scroll over the interactive chart and click on a particular atom to be able to review its data table.
  • Since many terms may be new, you can also familiarize yourself with each of them through this navigation guide.
  • Your students can also access this support by clicking on a particular term to learn more about it (however the language may be a bit high level for them).
• Set the expectation that for any number found in the T_1/2 [s] column should be written in scientific notation. This column will have really big numbers and really small numbers, so it makes it easier to quantify them.
• It’s also important to note that students might see a number written in scientific notation that doesn’t follow the rules of scientific notation that they have likely learned. For example, one of the isotopes gives the half- life as 100 x 10²⁴. Have your students rewrite this as 1.0 x 10²⁶ to practice consistency.
• Set an expectation for how many decimal places to include with the binding energy per nucleon. (It’s suggested to use one decimal place.)
• Students will likely have questions about which mode of decay to record for Fluorine-18 on the student worksheet. You can have students record both and follow-up by teaching them about isomeric transitions (IT), or you can have them only record the top mode of decay. For the purpose of this activity, it’s suggested to keep my students focused on simpler types of decay, and not focus on IT.
• Teachers may need to prompt students to help them recognize as many patterns as possible about stability of the nucleus and radioactive decay. Below are some possible patterns that students may bring up:
  • Isotopes that go through β+ decay have too many protons.
  • Isotopes that go through β- decay have too many neutrons.
  • The band of stability follows a certain ratio of protons to neutrons that keeps the nucleus together.
  • Isotopes closer to the middle or closer to the center of the band of stability are more stable.
  • The longer the half-life, the more stable the isotope.