Summary

In this lesson, students will review the concept of isotopes and apply the concepts of stability and relative abundance in order to determine the recent travels of a person of interest in a criminal investigation.

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
  • Engaging in Argument from Evidence

Objectives

By the end of this lesson, students should be able to

• Calculate the number of subatomic particles in different isotopes
• Calculate an element’s atomic mass based on relative abundance and mass numbers
• Define stable isotope
• Predict the origin of materials based on isotope analysis

Chemistry Topics

This lesson supports students’ understanding of

• subatomic particles
• atomic mass
• isotopes
• relative abundance
• nuclear stability

Time

Teacher Preparation: 15 minutes

Lesson: 60 minutes (about 20 minutes per worksheet)

Materials

• Three student worksheets per student
• Calculators
• Internet access or COLOR copies or projector
• Computer, tablet or phone with internet access
• https://teachchemistry.org/classroom-resources/isotopes-calculating-average-atomic-mass-simulation

Safety

No safety precautions needed

Teacher Notes

• The majority of this activity is a standard review of subatomic particles and initial lessons in isotopes and relative abundance.
• The “Isotopes & Calculating Average Atomic Mass” Simulation is used to help students calculate atomic mass.
• Teacher may wish to stop before extension and give examples of how the stable isotope maps work, perhaps pulling in another example (strontium example is listed in references) – this is particularly good for extensions. More information about the maps can be found in the “Teacher Notes 1” download in the sidebar.
• In the maps used, the ratios (R) are for hydrogen (²H/¹H) and oxygen (¹⁸O/¹⁶O). In most of the US, there is less deuterium than in the standard (δ²H is negative); there is more ¹⁸O than in the standard (δ¹⁸O is positive).
• The problem given on the worksheet is a bit more complex. A hair is found at a crime scene in central Wyoming. This area is part of the very dark blue sections of both maps and is a distinctive geographic region. The analysis of the hair shows that the end (the oldest part) originates from a bright red region in both maps – again distinctive.
• It is suggested that the teacher takes the students through a few different places – figuring out the deltas for those locations. Then, start the map, showing how the first one is from a dark blue area on both maps and locating that area.
• There are many potential paths through the US, but the source can only be Central Texas.There is one very logical straight line, but if a student supports his or her path with the correct isotope data, the student’s path should be considered correct. This is the path I drew (expand to see white dot path: