Fission vs Fusion

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Students will be able to explain the difference between fission and fusion, and explain how these processes relate to energy.

Big Idea

When the nuclei undergo fission (the splitting of an atom) or fusion (when two atoms combine) tremendous amounts of energy is released.


Unit Overview: This unit, called Passion, Power, and Peril, is an inter-disciplinary unit between two classes—English and Chemistry. In Chemistry class, students will learn about nuclear chemistry, but they will also research a specific aspect of the nuclear power industry. They will use this research in three ways. First, they will write a one-page paper for a Chemistry grade that explains how nuclear chemistry connects to the research topic. Second, students will write an informative/explanatory research paper that answers your research question by showing the complexity of the issue for an English grade. Finally, students will use their research and writing to create a piece of artwork for a multimedia art display designed to challenge the audience with weighing the costs and benefits of nuclear technology.

In this process we would like students to consider the following questions: How does society evaluate costs and benefits of a technology?  What are the costs and benefits of nuclear power plants? 

Lesson Overview: Commercial nuclear power plants operate using fission. In this lesson students will watch a video and read in order to be able to explain the difference between fission and fusion.

When the nuclei undergo fission (the splitting of an atom) or fusion (when two atoms combine) tremendous amounts of energy is released. Nuclear reactors rely primarily on fission.

This lesson aligns to the NGSS Disciplinary Core Idea of 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 by helping students understand two of the key terms in this idea (fission and fusion) and how these terms relate to the idea of energy.

It aligns to the NGSS Practice of the Scientist of Obtaining, evaluating, and communicating information (SP 8) because students spend most of this class obtaining information about nuclear processes

It aligns to the NGSS Crosscutting Concept of Energy and Matter because fission and fusion are both examples of how changes of energy and matter in a system can be described in terms of energy and matter flows into, out of, and within that system.

In terms of prior knowledge or skills, students should have a basic understanding of what an atomic nucleus is.

There are no special materials needed for this lesson, but it does rely on a projector to show a video.

Do Now/Activator

10 minutes

Do Now: Students come into class and are asked to read a selection similar to this article. In their notebooks they record possible reasons why a nuclear bomb is so much more powerful than a chemical bomb.

I reason that this is a good way to start class because I want to link the lesson that started this unit to today’s class. Many students were impressed with the power of a nuclear bomb, and I want them to begin to understand what nuclear power is.

Activator: I ask a student to share some ideas about why a nuclear bomb is so much more powerful than a chemical bomb, and in one class the student tells the class that nuclear bombs rely on splitting atoms instead of chemical bonds, and splitting atoms releases more energy than splitting bonds. In another class, I have to tease this out a little more with some guiding questions:

How do chemical bombs work?  (the splitting of chemical bonds)

How do nuclear bombs work? (the splitting of atoms)

In light of the fact that nuclear bombs are measured in terms of TNT equivalence, which type of bomb do you think releases more energy? (nuclear bombs)

I then show a video to introduce the ideas that students will read about and take notes. I have chosen this approach because I want to give students a mental image of fission and fusion, and the energy release associated with each of these concepts.



5 minutes

Mini-lesson: I then show the first slide of the Fission vs fusion slides  and I explain fission and fusion. I point out that tremendous energy is released in both cases.

I then ask students to spend time reading in their textbook about these two ideas and nuclear binding energy. I ask them to use the second slide to record in their notes information about fission and fusion. Their reading is similar to the content found in this article.

I ask them to spend about 15 minutes on this task because I would like them to have time to work on their nuclear research project, which they began in a previous lesson.


25 minutes

Student Activity: After 15 minutes I bring class together to review the questions that were asked. I project the 3rd and 4th slide and students correct their work. Most students were not able to answer the last question, which discussed the ease of fission and fusion from a technological perspective. I remind students that the video we watched noted that while fission is fairly easy, fusion is more challenging due to the need for high pressure and temperatures.

I used this approach because I want to make sure that all students have the same information. I use a timer because I do not feel that this work should take an entire class period. By naming the amount of time I expect students will need, I create more urgency than if I left the time open-ended.

Checking for understanding: While students are working I spend time walking around, and students anticipate this and check in with me about questions they have about the reading. This student work is typical of what students produced during this time.

After this review of the work is complete, I release students to work on their nuclear research project for 20 minutes. The research project is ongoing and I want students to think about it almost every day, so whenever I have some extra time in a lesson, this is a good way to fill that time.



10 minutes

To wrap this lesson up I bring some students together and ask them a series of questions:

  • What is fission?
  • What is fusion?
  • Which elements are involved in fission?
  • Which elements are involved in fusion?
  • What is nuclear binding energy?
  • Why does nuclear binding energy get released in fusion?
  • Why does nuclear binding energy get released in fission?


Ending class this way allows me to reemphasize what I want students to know, and it gives them a chance to relate what they learned in class on this day. Judging from this debrief video, students are coming along but will need to practice talking about and study this information in order to master the material.