Chapter 21 Notes- Nuclear Chemistry

21.1 Radioactivity[p.894]

  1. Background information
  2. Nuclear Chemistry- study of nuclear reactions.
  3. nucleons– protons and neutrons
  4. mass numbers determine the isotope of an element
  5. Stability of a nucleus is dependent on the proton to neutron ration.
  6. Nuclide is a nucleus with a specific number of protons and neutrons
  7. Radionuclides- nuclei that are radioactive
  8. Unstable and spontaneously decay emitting particles and electromagnetic radiation
  9. Emissions help unstable isotopes become more stable
  10. Radioisotopes – atoms containing these nuclei
  11. Nuclear Equations
  12. Alpha decay (alpha emission)= helium nucleus
  13. Radioactive decay = spontaneous decomposition of nuclei
  14. Example
  15. Note the sum of the mass numbers and atomic numbers for the products and reactants must be equal.
  16. Radioactive properties of a nucleus is independent of the chemical state of the atom
  17. Types of Radioactive Decay
  18. Alpha
  19. Symbol or
  20. Stream of helium-4 nuclei
  21. 2+ charge
  22. Relative penetrating power of 1
  23. Beta
  24. High speed electrons emitted from unstable nuclei
  25. Symbol or
  26. 1- charge
  27. Relative penetrating power of 100
  28. Beta emission is = to the conversion of a neutron to a proton
  29. Gamma
  30. High energy photons
  31. Does not change the value of the mass number or the atomic number
  32. Symbol or
  33. 0 charge
  34. Relative penetrating power of 10000
  35. Usually accompany other transmissions
  36. Generally not shown in nuclear equations
  37. Positron
  38. Has same mass and opposite charge of electron
  39. Symbol
  40. 1+ charge
  41. Positron emission converts a proton to a neutron
  42. Electron Capture
  43. Capture of an electron by the nucleus
  44. Symbol or
  45. 1- charge
  46. Appears on the reactant side

21.2 Patterns of Nuclear Stability [p.898]

  1. Neutron-to-Proton Ratio
  2. Nuclear force or strong force holds the nucleons hold together
  3. Necessary because protons in nucleus repel
  4. Neutrons play a role in establishing the strong force
  5. The greater the number of protons, the greater the number of neutrons needed for stability
  6. Belt of stability ends at bismuth
  7. All nuclei with 84 or more protons are radioactive
  8. Type of reaction depends largely on neutron: proton
  9. Nuclei above the belt of stability tend to emit beta particles to reducing the number of neutrons and increasing the number of protons to get closer to the 1:1
  10. Nuclei below the belt of stability (low n:p ) tend increase radios through positron emission or electron capture. Positron more common, but electron capture more common in large nuclear charge atoms
  11. Nuclei with atomic numbers 84 tend to undergo alpha emssions
  12. Radioactive series( Nuclear disintegrationseries)- series of nuclear reactions that end in stability
  13. Further Observations
  14. Magic Numbers-the number of protons and neutrons that are generally more stable
  15. 2,8,20,28,50, 82 protons
  16. 2,8, 20, 28, 50, 82 and 126 neutrons
  17. Nuclei with even numbers of protons and neutrons tend be more stable

21.3Nuclear Transmutations[p. 901]

  1. Background
  2. Nuclear reactions caused by a nucleus being struck by a neutron or another nucleus
  3. Rutherford performed the 1st conversion of a nucleus
  4. Transmutations usually written in the following order
  5. Target nucleus
  6. Bombarding particle
  7. Ejected particle
  8. Product nucleus
  9. Accelerating Charged particles
  10. Charged particles must be moving fast to overcome the repulsive force of the target nucleus
  11. Particle accelerators called “atom smashers” , cyclotrons , and synchrotrons are used accelerate the alpha particles
  12. Using Neutrons
  13. Not repelled by nucleus so acceleration is not needed
  14. Used in the development of most synthetic isotopes used in medicine and scientific research
  15. Transuranium Elements
  16. Elements with an atomic number above 92
  17. Short lived nuclei

21.4Rates of Radioactive Decay[p.903]

  1. General information
  2. Radioactive decay- 1st order kinetic process
  3. Half-live – time required for half of any substance to react
  4. Each element has its own characteristic half-life
  5. length of half-life varies greatly
  6. decay rate is unaffected by external conditions such as pressure, temperature, and state of chemical combination
  7. Radiometric dating-since radioactive decay is constant, half-life is used for dating objects
  8. C-14
  9. Used to date previously living specimens
  10. Measure the ratio of C-14:C-12 (amount of C-14 decreases after death)
  11. Can’t be used on objects over 50,000 years
  12. U-238
  13. Used to date rocks (nonliving materials)
  14. Measure ratio of U-238:Pb-206
  15. Calculations Based on Half -life
  16. Recall rate = kN where k= decay constant

N= number of nuclei

  1. Equations used

or

  1. Activity= rate at which a sample decays. Expressed in disintegrations/time
  2. Bequerrel (Bq) SI unit = 1 disintegration/ s
  3. Curie (Ci) = 3.7 x 1010disintegrations / second (rate of 1g of radium)

21.5Detection of Radioactivity[p.908]

  1. Film Badges – record extent of exposure to radiation
  2. Geiger Counters – measures the ionization of matter caused by radiation
  3. phospors – substances that give off light as electrons return to lower energy levels.
  4. Zinc sulfide – responds to alpha particles
  5. Measured using a scintillation counter
  6. Radio Tracers
  7. Uses a radioisotope to trace the path of an element
  8. Scintillation counters are used to follow the path

21.6Energy Changes in Nuclear Reactions[p. 911]

  1. Einstein’s Equation

c= speed of light 3.00x 108 m/s

m = mass in kg

  1. Indicates that mass and energy are proportional
  2. Due the constant of c2 being so large, the mass changes resulting large quantities of energy are very small.
  3. Mass in chemical reaction are too small to detect, but mass changes in nuclear reactions are much greater
  1. Nuclear Binding Energies
  2. Mass of nucleus and individual parts in the nucleus are always different
  3. Mass Defect – name given to the difference
  4. Nuclear binding energy- energy needed at separate the nucleons in a nucleus
  5. Larger the bonding energy the more stable the nucleus
  6. Changes in nuclear binding energy amounts indicate that heavy nuclei gain stability and therefore give off energy when split (fission)
  7. Fusion –method of fusing to masses together to generate energy.

21.7Nuclear Power: Fission [p. 870]

  1. General information
  2. Chain reaction- reactions that multiply by increasing the number of collisions with additional outside forces.
  3. Example – fission reactions started by a target nucleus and a neutron
  4. Can’t cause a violent explosion if left unchecked
  5. Chain stops if too many neutron are lost
  6. Critical Mass- amount of fissionable material large enough to maintain a chain reaction with a constant rate
  7. usually allows for 1neutron/each fission is effective in producing another fission
  8. super critical mass- mass in excess of a critical masss
  9. Nuclear Reactors
  10. Reactor basics
  11. Fuel – U-235 or UO2 pellets (typically enriched to about 3% U-235)
  12. Controls rods- regulate the flux of neutrons (typically cadmium and boron)
  13. Moderator- slows down neutrons so they can be more readily captured by the fuel
  14. Cooling liquid or gas- circulated through reactor to carry away heat generated
  15. Multiple styles of reactors exist
  16. Spent fuel
  17. Can be reprocessed
  18. Usually stored on site
  19. Must be stored until safe for human exposure (could take up to 600 years)
  20. If fuel rods are processed Plutonium -239can be recovered and reused
  21. Get deal of research being on disposal

21. 8 Nuclear Power Fusion[918]

  1. Fusion (thermonuclear reactions)occurs when energy is produced by the fusion of 2 light nuclei to form a heavier nuclei
  2. Appealing as an energy source
  3. Problem :
  4. requires high temperatures and pressures to work
  5. Difficulty to find a vessel to contain at such high temps
  6. Advantage: waste not radioactive

21.9 Radiation in the Enviroment and Living Systems [919]

  1. Types of radiation
  2. Ionizing Radiation
  3. Radiation removes an electron
  4. Harmful to biological systems
  5. Forms Free radical- substance with one or more unpaired electrons
  1. Nonionizing Radiation
  2. Usually lower energy (radiofrequency electromagnetic radiation or slow-moving neutrons)
  3. All radiation comes with some level of danger
  4. Greatest risk is at the sites that rapidly reproduce
  1. Radiation Doses
  2. Measured in Grays , rads, and rems
  3. Relative biological effectiveness- factor that measures the biological damage caused by radiation
  4. Effective doses are measured in Sievert
  5. Fatal exposure = 600rem
  6. Average 1 year exposure of a person to all natural sources = 360 mrem
  7. Radon
  8. Unreactive radioactive material found in the US
  9. Contributes to lung cancer
  10. Has a half-life of 3.82 days
  11. Decay particle Po-222 has half-life of 3.11 min which causes even greater danger
  12. Can test homes for Radon levels

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