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  • 1. Chemistry and Chemical Reactivity 6th Edition John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 23 Nuclear Chemistry Lecture written by John Kotz as modified by George Rhodes
  • 2. Chapter Goals p-1139
    • Identify radioactive elements and describe natural and artificial nuclear reactions
    • Calculate the binding energy and binding energy per nucleon for a particular isotope
    • Understand rates of radioactive decay
    • Understand artificial nuclear reactions
    • Understand issues of health and safety with respect to radioactivity
    • Become aware of their use in science and medicine
  • 3. Nuclear Chemistry Pictures of human heart before and after stress using gamma rays from radioactive Tc-99m
  • 4. Enrico Fermi
    • Nuclear physicist who worked on the Manhattan Style Clam Chowder Project. When asked later to explain why he was involved in such an endeavor, he replied, "I'm lactose intolerant."
  • 5. Or, Fermi
    • was an Italian physicist most noted for his work on beta decay, the development of the first nuclear reactor, and for the development of quantum theory. Fermi won the 1938 Nobel Prize for his work on induced radioactivity.
  • 6. ATOMIC COMPOSITION
    • Protons
      • + electrical charge
      • mass = 1.672623 x 10 -24 g
      • relative mass = 1.007 atomic mass units (amu)
    • Electrons
      • negative electrical charge
      • relative mass = 0.0005 amu
    • Neutrons
      • no electrical charge
      • mass = 1.009 amu
    • amu = as compared to 1 atom of carbon 12
  • 7. Isotopes
    • Atoms of the same element (same Z) but different mass number (A).
    • Boron-10 ( 10 B) has 5 p and 5 n: 10 5 B
    • Boron-11 ( 11 B) has 5 p and 6 n: 11 5 B
    10 B 11 B
  • 8. Radioactivity
    • One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934).
    • She discovered radioactivity , the spontaneous disintegration of some elements into smaller pieces.
    • Nobel/Physics 1903 for radiation phenomena and
    • Nobel/Chemistry 1911 for the discoveries of Ra and Po
  • 9. Types of Ionizing Radiation
  • 10. 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 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
  • 11. Penetrating Ability
  • 12. Nuclear Reactions
    • Ernest Rutherford* found Ra forms Rn gas when emitting an alpha particle.
    • 1902—Rutherford and Soddy proposed radioactivity is the result of the natural change of the isotope of one element into an isotope of a different element.
    • *Nobel/Chemistry 1908
  • 13. Nuclear Reactions
    • Alpha emission
    Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2. Nucleons are rearranged but conserved
  • 14. Nuclear Reactions
    • Beta emission
    Note that mass number (A) is unchanged and atomic number (Z) goes up by 1 . How does this happen? So, the e - ( β particle) is emitted while the proton remains with the nucleus
  • 15. 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 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
  • 16. 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 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
  • 17. 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 14 C 14 N + 0  +  6 7 -1 40 K 40 Ca + 0  +  19 20 -1 1 n 1 p + 0  +  0 1 -1 11 C 11 B + 0  +  6 5 +1 38 K 38 Ar + 0  +  19 18 +1 1 p 1 n + 0  +  1 0 +1  and  have A = 0 and Z = 0
  • 18. 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 37 Ar + 0 e 37 Cl +  18 17 -1 55 Fe + 0 e 55 Mn +  26 25 -1 1 p + 0 e 1 n +  1 0 -1 212 Po 4 He + 208 Pb 84 2 82 252 Cf 2 125 In + 2 1 n 98 49 0
  • 19. Gamma rays
    • Gamma rays are often produced alongside other forms of radiation such as alpha or beta. When a nucleus emits an α or β particle, the daughter nucleus is sometimes left in an excited state. It can then jump down to a lower level by emitting a gamma ray in much the same way that an atomic electron can jump to a lower level by emitting visible light or ultraviolet radiation.
  • 20. Radioactive Decay Series
  • 21. Other Types of Nuclear Reactions
    • Positron ( 0 +1  ): a positive electron
    K-capture: the capture of an electron from the first or K shell An electron and proton combine to form a neutron. 0 -1 e + 1 1 p --> 1 0 n 207 207
  • 22. Origin of the Elements
    • The Big Bang Theory
    • In the first moments there were only 2 elements — hydrogen and helium
  • 23. Stability of Nuclei
  • 24. Stability of Nuclei
    • H is most abundant element in the universe.
      • 88.6% of all atoms
      • He is 11.3% of all atoms
      • H + He = 99.9% of all atoms & 99% of mass of the universe.
    • This tells us about the origin of the elements, and so does the existence of isotopes.
  • 25. Elemental Abundance on Earth
  • 26. Isotopes
    • Hydrogen:
      • 1 1 H, protium
      • 2 1 H, deuterium
      • 3 1 H, tritium (radioactive)
    • Helium, 4 2 He
    • Lithium, 6 3 Li and 7 3 Li
    • Boron, 10 5 B and 11 5 B
    • Iron
      • 54 26 Fe, 5.82% abundant
      • 56 26 Fe, 91.66% abundant
      • 57 26 Fe, 2.19% abundant
      • 58 26 Fe, 0.33% abundant
  • 27. Isotopes
    • Hydrogen:
      • 1 1 H, protium
      • 2 1 H, deuterium
      • 3 1 H, tritium (radioactive)
    • Helium, 4 2 He
    • Lithium, 6 3 Li and 7 3 Li
    • Boron, 10 5 B and 11 5 B
    • Except for 1 1 H the mass number is always at least 2 x atomic number.
    • Repulsive forces between protons must be moderated by neutrons.
  • 28. Stability of Nuclei
    • Heaviest naturally occurring non-radioactive isotope is 209 Bi with 83 protons and 126 neutrons
    • There are 83 x 126 = 10,458 possible isotopes. Why so few actually exist?
  • 29. Stability of Nuclei
    • Up to Z = 20 (Ca), n = p (except for 7 3 Li, 11 5 B, 19 9 F)
    • Beyond Ca, n > p (A > 2 Z)
    • Above Bi all isotopes are radioactive. Fission leads to smaller particles, the heavier the nucleus the greater the rate.
    • Above Ca: elements of EVEN Z have more isotopes and most stable isotope has EVEN N.
  • 30. Stability of Nuclei
    • Out of > 300 stable isotopes:
    Even Odd Odd Even Z N 157 52 50 5 31 15 P 19 9 F 2 1 H, 6 3 Li, 10 5 B, 14 7 N, 180 73 Ta
  • 31. Stability of Nuclei
    • Suggests some PAIRING of NUCLEONS
    • There are “nuclear magic numbers”
      • 2 He 28 Ni
      • 8 O 50 Sn
      • 20 Ca 82 Pb
    Even Odd Odd Even Z N 157 52 50 5
  • 32. Band of Stability and Radioactive Decay Isotopes with low n/p ratio, below band of stability decay, decay by positron emission or electron capture 243 95 Am --> 4 2  + 239 93 Np  emission reduces Z  emission increases Z 60 27 Co --> 0 -1  + 60 28 Ni
  • 33. Binding Energy, E b E b is the energy required to separate the nucleus of an atom into protons and neutrons. For deuterium, 2 1 H 2 1 H ---> 1 1 p + 1 0 n E b = 2.15 x 10 8 kJ/mol E b per nucleon = E b /2 nucleons = 1.08 x 10 8 kJ/mol nucleons
  • 34. Calculate Binding Energy For deuterium, 2 1 H: 2 1 H ---> 1 1 p + 1 0 n Mass of 2 1 H = 2.01410 g/mol Mass of proton = 1.007825 g/mol Mass of neutron = 1.008665 g/mol =2.01649 ∆ m = 0.00239 g/mol From Einstein’s equation: E b = (∆m)c 2 = 2.15 x 10 8 kJ/mol E b per nucleon = E b /2 nucleons = 1.08 x 10 8 kJ/mol nucleons
  • 35. 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 -10 J BE = 2.37 x 10 -11 J = 1.25 x 10 -12 J BE + 19 F 9 1 p + 10 1 n 9 1 0 binding energy per nucleon = binding energy number of nucleons = 2.37 x 10 -11 J 19 nucleons
  • 36. E = mc2
    • To use this equation:
    • 1. convert mass defect to kg
    • 2. c= m/s or 3x10 8 then
    • 3. 3x10 8 squared = 9x 10 16 and this times the mass defect = J
  • 37. Binding Energy
  • 38. Binding Energy/Nucleon
  • 39. Half-Life Section 15.4
    • HALF-LIFE is the time it takes for 1/2 a sample to disappear.
    • The rate of a nuclear transformation depends only on the “reactant” concentration.
    • Concept of HALF-LIFE is especially useful for 1st order reactions.
  • 40. Half-Life Decay of 20.0 mg of 15 O. What remains after 3 half-lives? After 5 half-lives?
  • 41. Kinetics of Radioactive Decay
    • Activity (A) = Disintegrations/time = (k)(N)
    • where N is the number of atoms
    • Decay is first order , and so
    • ln (A/A o ) = -kt
    • The half-life of radioactive decay is
    • t 1/2 = 0.693/k
  • 42. Radiocarbon Dating
    • Radioactive C-14 is formed in the upper atmosphere by nuclear reactions initiated by neutrons in cosmic radiation
    • 14 N + 1 o n ---> 14 C + 1 H
    • The C-14 is oxidized to CO 2 , which circulates through the biosphere.
    • When a plant dies, the C-14 is not replenished.
    • But the C-14 continues to decay with t 1/2 = 5730 years.
    • Activity of a sample can be used to date the sample.
  • 43. Radiocarbon Dating t ½ = 5730 years Uranium-238 Dating t ½ = 4.51 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 + 8 4  + 6 0  92 -1 82 2
  • 44. Radiocarbon Dating
  • 45. Artificial Nuclear Reactions
    • New elements or new isotopes of known elements are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4 He and 11 B.
    • Reactions using neutrons are called n,  reactions because a  ray is usually emitted.
    • Radioisotopes used in medicine are often made by n,  reactions.
  • 46. Artificial Nuclear Reactions
    • Example of a n,  reaction is production of radioactive 31 P for use in studies of P uptake in the body.
    • 31 15 P + 1 0 n ---> 32 15 P + 
  • 47. Transuranium Elements
    • Elements beyond 92 (transuranium) made starting with an n,  reaction
    • 238 92 U + 1 0 n ---> 239 92 U + 
    • 239 92 U ---> 239 93 Np + 0 -1 
    • 239 93 Np ---> 239 94 Pu + 0 -1 
  • 48. Annual Waste Production 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
  • 49. Transuranium Elements & Glenn Seaborg 106 Sg
  • 50. Nuclear Fission
  • 51. Nuclear Fission Nuclear chain reaction 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 critical mass . Non-critical Critical
  • 52. Nuclear Fission
    • Fission chain has three general steps:
    • 1. Initiation. Reaction of a single atom starts the chain (e.g., 235 U + neutron)
    • 2. Propagation . 236 U fission releases neutrons that initiate other fissions
    • 3. Termination .
  • 53. Nuclear Fission Schematic diagram of a nuclear fission reactor
  • 54. Nuclear Fission & Lise Meitner 109 Mt
  • 55. Nuclear Fission & POWER
    • Currently about 103 nuclear power plants in the U.S. and about 435 worldwide.
    • 17% of the world’s energy comes from nuclear.
  • 56. Units for Measuring Radiation
    • Curie: 1 Ci = 3.7 x 10 10 distintegrations/s
    • SI unit is the becquerel: 1 Bq = 1 dps
    • Rad: measures amount of energy absorbed
    • 1 rad = 0.01 J absorbed/kg tissue
    • Rem: based on rad and type of radiation. Quantifies biological tissue damage
    • Usually use “millirem”
  • 57. Effects of Radiation
  • 58.  
  • 59. Nuclear Medicine: Imaging
  • 60. Nuclear Medicine: Imaging Technetium-99m is used in more than 85% of the diagnostic scans done in hospitals each year. Synthesized on-site from Mo-99. 99 42 Mo ---> 99m 43 Tc + 0 -1  99m 43 Tc decays to 99 43 Tc giving off  ray. Tc-99m contributes in sites of high activity.
  • 61. Nuclear Medicine: Imaging Imaging of a heart using Tc-99m before and after exercise.
  • 62. BNCT Boron Neutron Capture Therapy
    • 10 B isotope (not 11 B) has the ability to capture slow neutrons
    • In BNCT, tumor cells preferentially take up a boron compound, and subsequent irradiation by slow neutrons kills the cells via the energetic 10 B --> 7 Li neutron capture reaction (that produces a photon and an alpha particle)
    • 10 B + 1 n ---> 7 Li + 4 He + photon
  • 63. Food Irradiation
    • Food can be irradiated with  rays from 60 Co or 137 Cs.
    • Irradiated milk has a shelf life of 3 mo. without refrigeration.
    • USDA has approved irradiation of meats and eggs.
  • 64. Accelerator Transmutation of Waste
  • 65. Chemistry In Action: Nature’s Own Fission Reactor Natural Uranium 0.7202 % U-235 99.2798% U-238 Measured at Oklo 0.7171 % U-235
  • 66. Nuclear Fusion Fusion Reactions 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
  • 67. Particle Beam Fusion
    • If a high energy beam of electrons or other particles can be directed onto a tiny pellet or microballoon of deuterium-tritium mixture, it could cause it to explode like a miniature hydrogen bomb, fusing the deuterium and tritium nuclei in a time frame too short for them to move apart.
  • 68. Laser Fusion
    • Nova Laser System
    • Nova is the name given to the second generation laser fusion device at Lawrence Livermore Laboratories. It employs lasers ten times more powerful than the Shiva laser fusion device and will attempt to reach the breakeven point for fusion. Nova makes use of ten lasers which are focused on a 1 mm diameter target area, dumping 100,000 joules of energy into the target in a nanosecond.
    • As of 1994, Nova approached the Lawson criterion, but at a temperature too low for fusion ignition.
    • Once a critical ignition temperature for nuclear fusion has been achieved, it must be maintained at that temperature for a long enough confinement time at a high enough ion density to obtain a net yield of energy.
  • 69. Radioisotopes in Medicine
    • 1 out of every 3 hospital patients will undergo a nuclear medicine procedure
    • 24 Na, t ½ = 14.8 hr,  emitter, blood-flow tracer
    • 131 I, t ½ = 14.8 hr,  emitter, thyroid gland activity
    • 123 I, t ½ = 13.3 hr,  ray emitter, brain imaging
    • 18 F, t ½ = 1.8 hr,   emitter, positron emission tomography
    • 99m Tc, t ½ = 6 hr,  ray emitter, imaging agent
    Brain images with 123 I-labeled compound
  • 70. Geiger-M ü ller Counter
  • 71. 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
  • 72. 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 kilorads Inhibits 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