Nuclear chemistry

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Nuclear chemistry

  1. 1. Nuclear Chemistry
  2. 2. Radioactivity <ul><li>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). </li></ul><ul><li>She discovered radioactivity: the spontaneous disintegration of the nucleus of some elements into smaller pieces. </li></ul>
  3. 3. Nuclear Reactions vs. Normal Chemical Changes <ul><li>Nuclear reactions involve the nucleus </li></ul><ul><li>The nucleus loses particles, and protons and neutrons are rearranged </li></ul><ul><li>The disintegration of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy </li></ul><ul><li>“ Normal” Chemical Reactions involve electrons, not protons and neutrons </li></ul>
  4. 5. Types of Radiation <ul><li>Alpha ( ά ) – a positively charged helium isotope - we usually ignore the charge because it involves electrons, not protons and neutrons </li></ul><ul><li>Beta ( β ) – an electron </li></ul><ul><li>Gamma ( γ ) – pure energy; called a ray rather than a particle </li></ul>
  5. 6. Alpha Decay <ul><li>When a radioactive nucleus emits an alpha particle , a new nucleus forms that has: </li></ul><ul><li>a mass number that is 4 less than that of the initial nucleus. </li></ul><ul><li>an atomic number that is decreased by 2. </li></ul>
  6. 7. <ul><ul><li>Alpha Decay Nuclear Equation </li></ul></ul>Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings
  7. 8. <ul><li>In a balanced nuclear equation, the sum of the mass numbers and the sum of the atomic numbers for the nuclei of the reactant and the products must be equal. </li></ul><ul><li>MASS NUMBERS </li></ul><ul><li>Total = 251 = 251 </li></ul><ul><li>251 Cf 247 Cm + 4 He </li></ul><ul><li> 98 96 2 </li></ul><ul><li>Total = 98 = 98 </li></ul><ul><li> ATOMIC NUMBERS </li></ul>Balancing Nuclear Equations
  8. 9. Equation for Alpha Decay <ul><li>Write an equation for the alpha decay of 222 Rn. </li></ul><ul><li>STEP 1 Write the incomplete equation </li></ul><ul><li> 222 Rn ?s + 4 He </li></ul><ul><li> 86 2 </li></ul><ul><li>STEP 2 Determine the mass number 222 – 4 = 218 </li></ul><ul><li>STEP 3 Determine the atomic number 86 – 2 = 84 </li></ul><ul><li>STEP 4 Determine the symbol of element 84 = Po </li></ul><ul><li>STEP 5 Complete the equation </li></ul><ul><li> 222 Rn 218 Po + 4 He </li></ul><ul><li> 86 84 2 </li></ul>
  9. 10. Beta Decay <ul><li>A beta particle </li></ul><ul><li>is an electron emitted from the nucleus. </li></ul><ul><li>forms when a neutron in the nucleus breaks down. </li></ul><ul><li>1 n 0 e + 1 H </li></ul><ul><li>0 -1 1 </li></ul><ul><li> </li></ul>
  10. 11. <ul><li>STEP 1 Write an equation for the decay of 42 Potassium,a beta emitter. </li></ul><ul><li>42 K new nucleus + 0 e </li></ul><ul><li>19 -1 </li></ul><ul><li>STEP 2 Mass number : (same) = 42 </li></ul><ul><li>STEP 3 Atomic number: 19 + 1 = 20 </li></ul><ul><li>STEP 4 Symbol of element 20 = Ca </li></ul><ul><li>STEP 5 42 K 42 Ca + 0 e </li></ul><ul><li>19 20 -1 </li></ul>Writing An Equation for Beta Decay
  11. 12. Other Nuclear Particles <ul><li>Neutron </li></ul><ul><li>Positron – a positive electron </li></ul><ul><li>Proton – usually referred to as Hydrogen +1 </li></ul><ul><li>Any other elemental isotope </li></ul>
  12. 15. Half Life The time required for half of the nuclei in a sample of a specific isotope to undergo radioactive decay.
  13. 16. Half Lives for Radioactive Elements Radioactive Parent Stable Daughter Half life Potassium 40 Argon 40 1.25 billion yrs Rubidium 87 Strontium 87 48.8 billion yrs Thorium 232 Lead 208 14 billion years Uranium 235 Lead 207 704 million years Uranium 238 Lead 206 4.47 billion years Carbon 14 Nitrogen 14 5730 years
  14. 17. Half Life and radioactive dating
  15. 18. Half-Life Decay of 20.0 mg of 15 O. What remains after 3 half-lives? After 5 half-lives?
  16. 19. Learning Check! <ul><li>The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours? </li></ul>
  17. 20. <ul><li>In gamma radiation </li></ul><ul><li>energy is emitted from an unstable nucleus, indicated by m following the mass number. </li></ul><ul><li>the mass number and the atomic number of the new nucleus are the same. </li></ul><ul><li>99m Tc 99 Tc +  </li></ul><ul><li>43 43 </li></ul>Gamma (  ) Radiation
  18. 21. <ul><li>In position emission , </li></ul><ul><li>a proton is converted to a neutron and a positron. </li></ul><ul><li> 1 p 1 n + 0 e </li></ul><ul><li>1 0 +1 </li></ul><ul><li>the mass number of the new nucleus is the same, but the atomic number decreases by 1. </li></ul><ul><li>49 Mn 49 Cr + 0 e </li></ul><ul><li> 25 24 +1 </li></ul>Positron Emission
  19. 22. Why radiation is dangerous Radiation ionizes atoms in cell tissue and causes chemical reactions akin to decomposition / combustion. disrupts nucleotide sequences (your DNA is mutated)
  20. 23. Why radiation is dangerous
  21. 24. Measuring Radiation <ul><li>How radioactive a substance is refers to the number of nuclear disintegrations per second that occur in a sample. </li></ul><ul><li>SI unit is the Becquerel (Bq) which is 1 disintegration/second </li></ul><ul><li>The older unit, the Curie(Ci) : </li></ul><ul><li>1 Ci = 3.7 x 10 10 disintegrations per second </li></ul>
  22. 25. Measuring Radiation <ul><li>The 'rad ' is used to describe the energy quantity or dose of radiation absorbed. </li></ul><ul><li>rad (rd) stands for “radiation absorbed dose” </li></ul><ul><li>One rad defined as 10 -5 J/g of material. </li></ul>
  23. 26. Measuring Radiation Damage <ul><li>The rad does not account for the kind of damage done, only for how much radiation goes in. </li></ul><ul><li>To take into account this fact the REM was derived </li></ul><ul><li>To find the dose in REMS the dosage in rads is multiplied by a conversion factor that reflects the effectiveness of the kind of radiation causing the damage </li></ul>
  24. 27. Dosage in REMS Biological Effect : 25    notable change in blood cell components  100  radiation sickness - nausea, vomiting, decrease in white blood cell count, diarrhea, dehydration, prostration, hemorrhaging and loss of hair  200  the same as above but more pronounced in a shorter period of time  400  ½ of any population exposed to this dosage will be dead in 60 days  600  all exposed to this level will be dead in one week 
  25. 29. Chernobyl Anyone near the Chernobyl plant when it melted down received 400 rems also immediately. The day after 1 rem/hr was found in the nearest city. Normal background radiation is 1,000 times lower than this
  26. 31. Detecting radiation
  27. 32. Detecting radiation
  28. 33. Protection from radiation <ul><li>Wear lead infused suit. </li></ul><ul><li>Keep your distance. </li></ul><ul><ul><li>Inverse square law. </li></ul></ul><ul><ul><li>Intensity of radiation is inversely proportional to the square of the distance from the source </li></ul></ul>
  29. 34. Nuclear Fuel Uranium “Yellow Cake” U 3 O 8
  30. 35. Fission Neutron
  31. 36. Fission Chain Reaction
  32. 37. Representation of a fission process.
  33. 38. Nuclear Fission
  34. 39. Diagram of a nuclear power plant.
  35. 41. Nuclear Fission & POWER <ul><li>Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. </li></ul><ul><li>17% of the world’s energy comes from nuclear. </li></ul>
  36. 42. Fusion <ul><li>A process by which multiple like-charged atomic nuclei join together to form a heavier nucleus </li></ul>
  37. 43. Nuclear Fusion <ul><li>Fusion: </li></ul><ul><li>small nuclei combine </li></ul><ul><li>2 H + 3 H 4 He + 1 n + </li></ul><ul><li>1 1 2 0 </li></ul><ul><li>Occurs in the sun and other stars </li></ul>Energy
  38. 44. <ul><li>What radioactive isotope is produced in the following bombardment of boron? </li></ul><ul><li>10 B + 4 He ? + 1 n </li></ul><ul><li>5 2 0 </li></ul>Fusion
  39. 45. Nuclear Fusion <ul><li>Fusion </li></ul><ul><li>Excessive heat can not be contained </li></ul><ul><li>Attempts at “cold” fusion have FAILED. </li></ul><ul><li>“ Hot” fusion is difficult to contain </li></ul>
  40. 46. Artificial Nuclear Reactions <ul><li>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. </li></ul><ul><li>Reactions using neutrons are called  reactions because a  ray is usually emitted. </li></ul><ul><li>Radioisotopes used in medicine are often made by  reactions . </li></ul>
  41. 47. Artificial Nuclear Reactions <ul><li>Production of radioactive 31 P for use in studies of P uptake in the body. </li></ul><ul><li>31 15 P + 1 0 n ---> 32 15 P +  </li></ul>
  42. 48. Transuranium Elements <ul><li>Elements beyond 92 (transuranium) made starting with a  reaction </li></ul><ul><li>238 92 U + 1 0 n ---> 239 92 U +  </li></ul><ul><li>239 92 U ---> 239 93 Np + 0 -1  </li></ul><ul><li>239 93 Np ---> 239 94 Pu + 0 -1  </li></ul>
  43. 49. Nuclear Medicine: Imaging Thyroid imaging using Tc-99m
  44. 50. Food Irradiation <ul><li>Food can be irradiated with  rays from 60 Co or 137 Cs. </li></ul><ul><li>Irradiated milk has a shelf life of 3 mo. without refrigeration. </li></ul><ul><li>USDA has approved irradiation of meats and eggs. </li></ul>

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