1. Section 2: Nuclear Fission and Fusion
Preview
Key Ideas
Bellringer
Nuclear Forces
Nuclear Fission
Chain Reaction
Nuclear Fusion

2. Key Ideas What holds the nuclei of atoms together?
What is released when the nucleus of a heavy atom is split?
What happens when the nuclei of small atoms are joined?

3. Bellringer
In your study of chemical reactions, you learned that one convenient way to classify reactions was as synthesis or decomposition. In synthesis reactions, the products are larger and more complex than the reactants. In decomposition reactions, the opposite is true.
In some situations, nuclear reactions can occur. These reactions can also be categorized by how the product nuclei compare to the reactant nuclei. Study the models of the nuclei shown on the next slide, and answer the following questions.

4. Bellringer, continued

5. Bellringer, continued
1. In which of the diagrams did a complex nucleus form simpler nuclei?
2. In which of the diagrams did simple nuclei combine to form a complex nucleus?
3. Each year, scientists around the world attempt to “discover” new elements using nuclear reactions. Which of the reactions shown in the diagrams above most likely would be useful for this type of research? Explain your answer.

6. SPS3.b Differentiate between fission and fusion.

7. EQ: How do fission and fusion differ?

8. What holds the nuclei of atoms together?
Nuclear Forces
What holds the nuclei of atoms together?

9. Nuclear Forces
The stability of a nucleus depends on the nuclear forces that act between protons and neutorons and hold the nucleus together.

10. 10-2-2 Nuclear Forces, continued
strong nuclear force: causes protons and neutrons in the nucleus to attract each other

11. 10-2-3 Nuclear Forces, continued
Neutrons contribute to nuclear stability.

12. 10-2-4 Nuclear Forces, continued
Nuclei with more than 83 protons are always unstable.

13. Nuclear Forces, continued

14. What is released when the nucleus of a heavy atom is split?
Nuclear Fission
What is released when the nucleus of a heavy atom is split?

15. Nuclear Fission
fission: the process by which a nucleus splits into two or more fragments and releases neutrons and energy

16. 10-2-6 Nuclear Fission, continued
Fission of Uranium-235:

17. 10-2-7 Nuclear Fission, continued
According to Einstein’s equation, E = mc2 , mass is converted to energy in a fission reaction.

18. 10-2-8 Nuclear Fission, continued
mass defect: the difference in the total measured mass of a nucleus and the sum of the individual masses of the neutrons and protons that make up the nucleus

19. 10-2-9 Nuclear Fission, continued
The mass defect is the amount of mass that has been changed to energy.

20. 10-2-9 Nuclear Fission, continued
nuclear chain reaction: a continuous series of nuclear fission reactions caused by the release of electrons

21. 10-2-10 Nuclear Fission, continued
critical mass: the minimum mass of a fissionable isotope that provides the number of neutrons needed to sustain a chain reaction

22. Chain Reaction

23. What happens when the nuclei of small atoms are joined?
Nuclear Fusion
What happens when the nuclei of small atoms are joined?

24. Nuclear Fusion
fusion: the process in which light nuclei combine at extremely high temperatures, forming heavier nuclei and releasing energy

25. 10-2-12 Nuclear Fusion, continued
In stars, energy is produced when hydrogen nuclei combine.

26. 10-2-13 Nuclear Fusion, continued
A large amount of energy and a very high temperature is needed to start a fusion reaction.

27. 10-2-14 Nuclear Fusion, continued
Four hydrogen atoms combine to make a helium atom and high-energy gamma rays in a three-step process.

28. 10-2-15 Nuclear Fusion, continued
Fusion reactions are not practical now because of the difficulty of containing such a high temperature reaction.

29. 10-2-16 Nuclear Fusion, continued
Two big advantages of fusion are they produce more energy than fission and they don’t make hazardous wastes.

30. Nuclear Fusion, continued