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Chapter 21 Nuclear Chemistry

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  • 1. Nuclear Chemistry Chapter 21 Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.
  • 2. Radioactivity
    • _________________—unstable atomic nuclei spontaneously emit particles, electromagnetic radiation (EMR), or both
    • ________________________—results from bombarding nuclei with neutrons, protons, or other nuclei
  • 3. ______________ (Z) = number of protons in nucleus ______________ (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons A Z 21.1 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
  • 4. What is the difference between and 21.1 p.673 represents an electron in or from an atomic orbital represents an electron that is physically identical to an electron in or from an atomic orbital, but this electron comes from the decay of a neutron to a proton and an electron—it is also called a beta particle or ray 0 e +1 0  +1 0 e +1 0  +1
  • 5. 21.1 Comparison of Chemical Reactions and Nuclear Reactions
  • 6. 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 21.1 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
  • 7. 212 Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212 Po. 212 = 4 + A A = 208 84 = 2 + Z Z = 82 21.1 Ex 21.1, p.673 4 He 2 4  2 or alpha particle - 212 Po 4 He + A X 84 2 Z 212 Po 4 He + 208 Pb 84 2 82
  • 8. Nuclear Stability and Radioactive Decay Beta decay 1 n 1 p + 0  +  0 -1 ________ # of ________ by 1 ________ # of ________ by 1 Positron decay 1 p 1 n + 0  +  1 0 +1 ________ # of ________ by 1 ________ # of ________ by 1 21.2 1 14 C 14 N + 0  +  6 7 -1 40 K 40 Ca + 0  +  19 20 -1 11 C 11 B + 0  +  6 5 +1 38 K 38 Ar + 0  +  19 18 +1  and  have A = 0 and Z = 0
  • 9. Electron capture decay ________ # of ________ by 1 ________ # of ________ by 1 Nuclear Stability and Radioactive Decay 1 p + 0 e 1 n +  1 0 -1 Alpha decay ________ # of ________ by 2 ________ # of ________ by 2 Spontaneous fission 21.2 37 Ar + 0 e 37 Cl +  18 17 -1 55 Fe + 0 e 55 Mn +  26 25 -1 212 Po 4 He + 208 Pb 84 2 82 252 Cf 2 125 In + 2 1 n 98 49 0
  • 10. Nuclear Stability
    • Certain numbers of neutrons and protons are extra stable
      • 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
    21.2 Number of Stable Isotopes with Even and Odd Numbers of Protons and Neutrons
  • 11. n/p too large beta decay n/p too small positron decay or electron capture 21.2 p.675 X Y
  • 12. ______________________ is the energy required to break up a nucleus into its component protons and neutrons. BE is an indication of the stability of a nucleus. In order to compare nuclei of two different isotopes/elements, we must take into account the fact that they have different numbers of _________. For this reason, nuclear binding energy per nucleon is more useful. 21.2 p.676
  • 13. Mass Defect The difference between the ________________ of an atom and the ________________ of the masses of protons, neutrons, and electrons What does the mass defect tell us? How much mass was changed to energy in the formation of the atom. p.676
  • 14. The Law of Charges tells us…? So how can all those positively charged protons be crammed into the tiny space of the nucleus? We call it the “strong nuclear force” or just the “strong force.” Some of the mass of the nucleons is converted to energy and lost. This is the general idea behind fusion: Build new, larger nuclei and release great amounts of energy!
  • 15. Nuclear binding energy per nucleon vs Mass number 21.2 p.678 note nuclear binding energy nucleon nuclear stability
  • 16.
    • Which element has the greatest net attractive forces among its nucleons? (graph)
    • Radioactivity: unstable nuclei spontaneously emit particles, electromagnetic radiation (EMR), or both
    • Main types of radioactivity:
      •  particles (He 2+ )
      •  particles (e - )
      •  rays (short-wavelength emr)
      • positron emission
      • electron capture
    • Often it involves a multi-step sequence, a series…. and all obey first-order kinetics.
  • 17. Kinetics of Radioactive Decay rate =  N N = N 0 exp( -  t ) lnN = lnN 0 -  t N = the number of atoms at time t N 0 = the number of atoms at time t = 0  is the decay or rate constant 21.3 The Uranium Decay Series N daughter rate = -  N  t  N  t =  N - ln2 = t ½ 
  • 18. Kinetics of Radioactive Decay [N] = [N] 0 exp( -  t ) ln[N] = ln[N] 0 -  t 21.3  is the first order rate constant and N is the number of radioactive nuclei present at time t p.679f [N] ln [N]
  • 19. Radiometric Assumptions The method measures the parent/daughter ratio of the elements. 1. The system must initially contain none of ____________________________________ . 2. The decay rate must _______________________ . 3. The amounts of the parent element and the daughter products must be affected by ___________________________________ .
  • 20. Radiocarbon Dating t ½ = 5730 years Uranium-238 Dating t ½ = 4.51 x 10 9 years 21.3 p.681f Potassium-40 Dating t ½ = 1.2 x 10 9 years 14 N + 1 n 14 C + 1 H 7 1 6 0 14 C 14 N + 0  +  6 7 -1 238 U 206 Pb + 4  + 6 0  92 -1 82 2 40 K + 0 e 40 Ar 19 18 -1
  • 21. Nuclear Transmutation 21.4 p.683 Cyclotron Particle Accelerator 14 N + 4  17 O + 1 p 7 2 8 1 27 Al + 4  30 P + 1 n 13 2 15 0 14 N + 1 p 11 C + 4  7 1 6 2
  • 22. Nuclear Transmutation 21.4 The Transuranium Elements
  • 23. Nuclear Fission 21.5 Energy = [mass 235 U + mass n – (mass 90 Sr + mass 143 Xe + 3 x mass n )] x c 2 Energy = 3.3 x 10 -11 J per 235 U = 2.0 x 10 13 J per mole 235 U Combustion of 1 ton of coal = 5 x 10 7 J p.685f 235 U + 1 n 90 Sr + 143 Xe + 3 1 n + Energy 92 54 38 0 0
  • 24. Nuclear Fission 21.5 Representative fission reaction p.686 235 U + 1 n 90 Sr + 143 Xe + 3 1 n + Energy 92 54 38 0 0
  • 25. Nuclear Fission 21.5 A ________________________ is a self-sustaining sequence of nuclear fission reactions. The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the ________________________. Non-critical Critical
  • 26. Nuclear Fission 21.5 Schematic diagram of a nuclear fission reactor
  • 27. Annual Waste Production 21.5 Nuclear Fission 35,000 tons SO 2 4.5 x 10 6 tons CO 2 1,000 MW coal-fired power plant 3.5 x 10 6 ft 3 ash 1,000 MW nuclear power plant 70 ft 3 vitrified waste
  • 28. 21.5 Nuclear Fission Hazards of the radioactivities in spent fuel compared to uranium ore From “Science, Society and America’s Nuclear Waste,” DOE/RW-0361 TG
  • 29. 21.6 Nuclear Fusion Fusion Reaction Energy Released 6.3 x 10 -13 J 2.8 x 10 -12 J 3.6 x 10 -12 J Tokamak magnetic plasma confinement 2 H + 2 H 3 H + 1 H 1 1 1 1 2 H + 3 H 4 He + 1 n 1 1 2 0 6 Li + 2 H 2 4 He 3 1 2
  • 30. 21.6 Radioisotopes in Medicine
    • 1 out of every 3 hospital patients will undergo a nuclear medicine procedure
    • 24 Na, t ½ = 14.8 hr,  emitter, _______________________
    • 131 I, t ½ = 14.8 hr,  emitter, ________________________
    • 123 I, t ½ = 13.3 hr,  ray emitter, _____________________
    • 18 F, t ½ = 1.8 hr,   emitter, ________________________
    • 99m Tc, t ½ = 6 hr,  ray emitter, _____________________
    Brain images with 123 I-labeled compound
  • 31. 21.6 Biological Effects of Radiation R adiation a bsorbed d ose ( rad ) 1 rad = 1 x 10 -5 J/g of material R oentgen e quivalent for m an ( rem ) 1 rem = 1 rad x Q Q uality Factor  -ray = 1  = 1  = 20 Average Yearly Radiation Doses for Americans
  • 32. Biological Effects of Radiation Formation of _______________ and/or ________________ that attack membranes, enzymes, or DNA. Damage can be ________________ or _______________. p.695f