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

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?

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.

Bellringer, continued

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.

SPS3.b Differentiate between fission and fusion.

EQ: How do fission and fusion differ?

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

10-2-1 Nuclear Forces The stability of a nucleus depends on the nuclear forces that act between protons and neutorons and hold the nucleus together.

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

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

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

Nuclear Forces, continued

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?

10-2-5 Nuclear Fission fission: the process by which a nucleus splits into two or more fragments and releases neutrons and energy

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

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

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

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

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

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

Chain Reaction

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

10-2-11 Nuclear Fusion fusion: the process in which light nuclei combine at extremely high temperatures, forming heavier nuclei and releasing energy

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

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

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.

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

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.

Nuclear Fusion, continued