Lecture Notes Alan D. Earhart Southeast Community College Lincoln, NE Chapter 22 Nuclear Chemistry John E. McMurry Robert C. Fay CHEMISTRY Fifth Edition Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 22/2 Nuclear Reactions and Their Characteristics Nuclear Chemistry: The study of the properties and reactions of atomic nuclei. Nucleon: A generic term for a nuclear particles- both protons (p) and neutrons (n).
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/3 Nuclear Reactions and Their Characteristics Isotope: Atoms with identical atomic numbers but different mass numbers. Nuclide: The nucleus of a given isotope. A carbon-12 nuclide.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/4 Nuclear Reactions and Their Characteristics Nuclear Reaction: A reaction that changes an atomic nucleus. Nitrogen-14 nuclideCarbon-14 nuclide e 0 C 14 N 7 +
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/5 Nuclear Reactions and Their Characteristics A nuclear reaction changes an atom’s nucleus. A chemical reaction only changes the distribution of electrons. Different isotopes of an elements have essentially the same behavior in chemical reactions. The rate of a nuclear reaction is unaffected by temperature, pressure, or catalysts. A nuclear reaction of an atom is essentially the same, regardless of whether the atom is uncombined or in a chemical compound The energy change accompanying a nuclear reaction is far greater than that accompanying a chemical reaction. Comparisons Between Nuclear and Chemical Reactions
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/6 Nuclear Reactions and Radioactivity Radioactivity: The spontaneous emission of radiation in a nuclear reaction. Radionuclide: A radioactive nuclei. Radioisotope: A radioactive isotope.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/7 Nuclear Reactions and Radioactivity
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/8 Nuclear Reactions and Radioactivity Alpha ( ) Radiation An alpha particle is a helium-4 nucleus (2 protons and 2 neutrons). Alpha particle,
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/9 Nuclear Reactions and Radioactivity In nuclear equations, the nucleons must balance. 234 nucleons 90 protons 238 nucleons 92 protons 4 nucleons 2 protons +
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/10 Nuclear Reactions and Radioactivity Beta ( ) Radiation A beta particle is an electron. Beta particle, -
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/11 Nuclear Reactions and Radioactivity Positron Emission Gamma ( ) Radiation A gamma particle is a high-energy photon A positron has the same mass as an electron but an opposite charge. It can be thought of as a “positive electron.” Positron, +
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/12 Nuclear Reactions and Radioactivity Electron Capture A process in which the nucleus captures an inner- shell electron, thereby converting a proton to a neutron.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/13 Nuclear Reactions and Radioactivity
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/14 Radioactive Decay Rates Radioactive decay is a first-order process. N N0N0 ln= -kt N0N0 is the number of radioactive nuclei initially present in a sample. kis the decay constant. Decay = k x N Nis the number of radioactive nuclei remaining at time t.
Radioactive Decay Rates Radioactive decay is a first-order process.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/16 Radioactive Decay Rates Radioactive decay is a first-order process. k = t 1/2 ln 2 or t 1/2 = k ln 2 Half-life:
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/17 Radioactive Decay Rates
Nuclear Stability
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/19 Nuclear Stability Every element in the periodic table has at least one radioactive isotope. Hydrogen is the only element whose most abundant stable isotope, hydrogen-1, contains more protons (1) than neutrons (0). The ratio of neutrons to protons gradually increases for elements heavier than calcium. All isotopes heavier than bismuth-209 are radioactive, even though they may occur naturally.
Nuclear Stability
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/21 The increasing ratio of neutrons to protons suggests that neutrons act as a “glue” to hold the nuclei together.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/22 There appear to be certain “magic numbers” of protons or neutrons—2, 8, 20, 28, 50, 82, 126—that give rise to particularly stable nuclei.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/23 Elements with an even atomic number have larger numbers of nonradioactive isotopes than do elements with odd atomic numbers.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/24
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/25
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/26 Nuclear Stability These processes increase the neutron/proton ratio: Neutron Electron capture: Proton + Electron This process decreases the neutron/proton ratio: Proton + - Beta emission:Neutron Proton + + Alpha emission: NeutronPositron emission: X Z A Y Z - 2 A He 2 4
Nuclear Stability Decay Series: A series of nuclear disintegrations ultimately leading to a nonradioactive product.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/28 Energy Changes During Nuclear Reactions Mass Defect: The loss in mass that occurs when protons and neutrons combine to form a nucleus. The loss in mass is converted into energy that is released during the nuclear reaction and is thus a direct measure of the binding energy holding the nucleons together. E = ? 2 + n 0 1 2H 1 1 He 2 4
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/29 Energy Changes During Nuclear Reactions Because of the interconversion of mass and energy, the law of conservation of mass and the law of conservation of energy must be combined. The combination of mass and energy must be conserved.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/30 Nuclear Fission and Fusion Very heavy nuclei can gain stability and release energy by fragmenting to yield midweight particles—nuclear fission. Very light nuclei can gain stability and release energy by fusing—nuclear fusion.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/31 Nuclear Fission and Fusion Nuclear Fission
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/32 Nuclear Fission and Fusion Chain Reaction: A self-sustaining reaction whose product initiates further reaction. Nuclear Fission U Kr n 0 1 n Ba
Nuclear Fission and Fusion
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/35 Nuclear Fission and Fusion Nuclear Fusion Among the processes thought to occur in the Sun: H 1 2 H He 2 3 H 1 1 e 1 0 H H H e H 1 1
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/36 Nuclear Fission and Fusion Advantages: Relatively cheap fuel source and the products are nontoxic. Disadvantage: A temperature of 40 million kelvins is needed to initiate the process. Nuclear Fusion
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/37 Nuclear Transmutation Nuclear Transmutation: The change of one element into another. Plutonium-241 can be made by bombarding uranium-238 with alpha particles: Pu Am e 0 Plutonium-241 decays into americium-241: He 2 4 U Pu n 0 1
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/38 Nuclear Transmutation Nuclear Transmutation: The change of one element into another. Cobalt-60 is used in radiation therapy for cancer patients. The overall preparation process can be written as: 2Fe Co e 0 n 0 1
Detecting and Measuring Radioactivity Ion + e - Molecule Radiation Ionizing Ionizing Radiation: Radiation that knocks an electron from a molecule, thereby ionizing it.
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/40 Detecting and Measuring Radioactivity Geiger Counter
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/41 Biological Effects of Radiation
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/42 Biological Effects of Radiation
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/43 Applications of Nuclear Chemistry Dating with Radioisotopes Carbon-14 eventually enters the food chain via the formation of carbon dioxide and its uptake by plants via photosynthesis. Eating these plants distributes carbon-14 throughout all living organisms. Radioactive carbon-14 is constantly being generated in the upper atmosphere by neutron bombardment: n 0 1 N C 6 + H 1 1
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/44 Applications of Nuclear Chemistry The half-life of carbon-14 is 5730 years: The measured ratio of carbon-14/carbon-12 after death can determine how long ago the organism died. Dating with Radioisotopes e 0 C 14 N 7 +
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/45 Applications of Nuclear Chemistry Geologic age can be determined by analysis of potassium-40: Dating with Radioisotopes e 1 0 K Ar e 0 K Ar
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/46 Applications of Nuclear Chemistry In Vivo Procedures Determination of whole-blood volume using red blood cells labeled with chromium-51. Therapeutic Procedures Irradiation of tumors using gamma rays emitted from cobalt-60. Beta emission of iodine-131 to treat thyroid disease. Medical Uses of Radioactivity
Copyright © 2008 Pearson Prentice Hall, Inc.Chapter 22/47 Applications of Nuclear Chemistry Imaging Procedures Use of a radiopharmaceutical agent known to concentrate in a specific tissue or organ. These target areas show up as “hot” spots compared to a “cold” background. Technetium-99m is the most widely used radioisotope. Medical Uses of Radioactivity