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  • 1. Nuclear Chemistry Chapter 23 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Atomic number(Z) = number of protons in nucleus Mass number(A) = number of protons + number of neutrons=atomic number (Z) + number of neutrons A Z 1 1 1 0 0 -1 0 +1 4 2 23.1 X A Z Mass Number Atomic Number Element Symbol 1 p 1 1 H 1 or proton 1 n 0 neutron 0 e -1 0 -1 or electron 0 e +1 0 +1 or positron 4 He 2 4 2 or particle 3. Balancing Nuclear Equations

  • Conserve mass number (A).

The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants. 235 + 1 = 138 + 96 + 2x1

  • Conserve atomic number (Z) or nuclear charge.

The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants. 92 + 0 = 55 + 37 + 2x0 23.1 1 n 0 U 235 92 + Cs 138 55 Rb 96 37 1 n 0 + + 2 1 n 0 U 235 92 + Cs 138 55 Rb 96 37 1 n 0 + + 2 4. 212 Po decays by alpha emission.Write the balanced nuclear equation for the decay of212 Po. 212 = 4 + A A = 208 84 = 2 + Z Z = 82 23.1 4 He 2 4 2 or alpha particle -212 Po4 He +A X 84 2 Z 212 Po4 He +208 Pb 84 2 82 5. 23.1 6. Nuclear Stability and Radioactive Decay Beta decay Decrease # of neutrons by 1 Increase # of protons by 1 Positron decay Increase # of neutrons by 1 Decrease # of protons by 1 23.2 14 C14 N +0 + 6 7 -1 40 K40 Ca +0 + 19 20 -1 1 n1 p +0 + 0 1 -1 11 C11 B +0 + 6 5 +1 38 K38 Ar +0 + 19 18 +1 1 p1 n +0 + 1 0 +1 andhave A = 0 and Z = 0 7. Electron capture decay Increase # of neutrons by 1 Decrease # of protons by 1 Nuclear Stability and Radioactive Decay Alpha decay Decrease # of neutrons by 2 Decrease # of protons by 2 Spontaneous fission 23.2 37 Ar +0 e37 Cl + 18 17 -1 55 Fe +0 e55 Mn + 26 25 -1 1 p +0 e1 n + 1 0 -1 212 Po4 He +208 Pb 84 2 82 252 Cf2 125 In + 2 1 n 98 49 0 8. n/p too large beta decay n/p too small positron decay or electron capture 23.2 X Y 9. Nuclear Stability

  • Certain numbers of neutrons and protons areextrastable
    • n or p = 2, 8, 20, 50, 82 and 126
    • Like extra stable numbers of electrons in noble gases (e -= 2, 10, 18, 36, 54 and 86)
  • Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protons
  • All isotopes of the elements with atomic numbers higher than 83 are radioactive
  • All isotopes of Tc and Pm are radioactive

23.2 10. Nuclear binding energy (BE)is the energy required to break up a nucleus into its component protons and neutrons. BE = 9 x (p mass) + 10 x (n mass) 19 F mass E = mc 2 BE (amu)= 9 x 1.007825 + 10 x 1.008665 18.9984 BE = 0.1587 amu 1 amu = 1.49 x 10 -10J BE = 2.37 x 10 -11 J = 1.25 x 10 -12J 23.2 BE +19 F9 1 p + 10 1 n 9 1 0 binding energy per nucleon =binding energy number of nucleons =2.37 x 10 -11J 19 nucleons 11. Nuclear binding energy per nucleon vs Mass number 23.2 nuclear binding energy nucleon nuclear stability 12. Nuclear Fission 23.5 Energy = [mass235 U + mass n (mass90 Sr + mass143 Xe + 3 x mass n )] x c 2 Energy = 3.3 x 10 -11 J per235 U = 2.0 x 10 13J per mole235 U Combustion of 1 ton of coal = 5 x 10 7J 235 U +1 n90 Sr +143 Xe + 3 1 n + Energy 92 54 38 0 0 13. Nuclear Fission 23.5 Representativefission reaction 235 U +1 n90 Sr +143 Xe + 3 1 n + Energy 92 54 38 0 0 14. Nuclear Fission 23.5 Nuclear chain reactionis a self-sustaining sequence of nuclear fission reactions. The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is thecritical mass . Non-critical Critical 15. Nuclear Fission 23.5 Schematic diagram of a nuclear fission reactor 16. Annual Waste Production 23.5 Nuclear Fission 35,000 tons SO 2 4.5 x 10 6tons CO 2 1,000 MW coal-fired power plant 3.5 x 10 6ft 3ash 1,000 MW nuclear power plant 70 ft 3vitrified waste 17. 23.6 Nuclear Fusion Fusion Reaction Energy Released 6.3 x 10 -13J 2.8 x 10 -12J 3.6 x 10 -12J Tokamak magnetic plasma confinement 2 H +2 H3 H +1 H 1 1 1 1 2 H +3 H4 He +1 n 1 1 2 0 6 Li +2 H24 He 3 1 2 18. 23.7 Radioisotopes in Medicine

  • 1 out of every 3 hospital patients will undergo a nuclear medicine procedure
  • 24 Na, t = 14.8 hr,emitter, blood-flow tracer
  • 131 I, t = 14.8 hr,emitter, thyroid gland activity
  • 123 I, t = 13.3 hr, ray emitter, brain imaging
  • 18 F,t = 1.8 hr, emitter, positron emission tomography
  • 99m Tc,t = 6 hr, ray emitter, imaging agent

Brain images with123 I-labeled compound 19. Geiger-M ller Counter 23.7 20. 23.8 Biological Effects of Radiation R adiationa bsorbedd ose ( rad ) 1 rad = 1 x 10 -5J/g of material R oentgene quivalent form an ( rem ) 1 rem = 1 rad x Q Q uality Factor -ray = 1 = 1 = 20 21. Chemistry In Action:Food Irradiation Sterilizes meat, poultry and fish. Kills insects and microorganisms in spices and seasoning. 1000 to 10,000 kilorads Delays spoilage of meat poultry and fish. Reduces salmonella. Extends shelf life of some fruit. 100 1000 kiloradsInhibits sprouting of potatoes, onions, garlics. Inactivates trichinae in pork. Kills or prevents insects from reproducing in grains, fruits, and vegetables. Up to 100 kilorad Effect Dosage

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