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AP Chemistry Chapter 23 Notes

AP Chemistry Chapter 23 Notes. Henri Becquerel ruined some photographic plates with x-rays from a uranium source and radioactive decay was discovered in 1896. Henri Becquerel’s experiment – (1896)

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AP Chemistry Chapter 23 Notes

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  1. AP Chemistry Chapter 23 Notes

  2. Henri Becquerel ruined some photographic plates with x-rays from a uranium source and radioactive decay was discovered in 1896.

  3. Henri Becquerel’s experiment – (1896) Tried to see if fluorescent minerals would give off X-rays. Set some out in the sun with covered photographic film. If minerals gave of X-rays when they fluoresced, the film should darken – and it did. Accidentally set some of these minerals in a dark drawer for a few days with undeveloped film, and was surprised to see the film strongly exposed. He knew they gave off X-rays when charged by the sun - but these results suggested the X-rays were coming from the mineral itself – Natural Radioactivity – No external energy source required!

  4. 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.

  5. Marie and Pierre Curie’s experiments with pitchblende – Discovered Radioactive Naturally occurring elements, particularly Uranium, Radium, and Polonium. Curium was named after Marie posthumously

  6. THE GREAT DISCOVERYW.K. Roentgen’s experiment (1895) - Fluorescence –Certain substances will absorb photons of energy when exposed to a source (i.e. cathode rays, the sun), and then emit them over a period of time – thus they glow in dark when exposed to UV light Cathode rays –beams of electronsCathode ray tube (CRT) –Vacuum tube that has electric current passed through it . Component of television sets –that’s why they call it “the tube” X-rays –Name given by Roentgen to unusual stray energy observed to cause fluorescence across the room when CRT was used… X-ray because he did not know what the heck it was….and the name stuck

  7. BETA PARTICLES • Consists of – high speed electron (from disintegration of neutron) • Tissue damage potential – much greater than Alpha • Harmful if ingested? – not as much as Alpha • Can be blocked? – by glass, will penetrate skin

  8. GOLD FOIL EXPERIMENTErnest Rutherford and the Gold Foil Experiment Disproved Thompson’s plum pudding model Proved the existence of a nucleus with a positive charge 

  9. ALPHA PARTICLES • Consists of – He nucleus • Tissue damage potential – great – if internalized • Harmful if ingested? – yup, very • Can be blocked? – by layer of skin, or cardboard • Note that atoms are NOT conserved in nuclear reactions, but mass numbers and atomic numbers are.

  10. NUCLEAR RADIATIONErnest Rutherford and the Lead block experiment (1899) -Alpha rays ()Beta rays ()–Gamma rays ()

  11. How did Rutherford’s gold foil experiment change the theory of the structure of the atom? Thompson 1906 Rutherford 1913 Bohr 1924

  12. ARCHITECTURE OF THE ATOM • Atomic Number – Number of protons • Determine what type of element an atom is • Mass Number – Sum of total number of protons and neutrons in an atom • Can change for an element depending upon the number of neutrons present • Isotopes – Elements with the same atomic number, but different mass numbers • Due to the difference in number of neutrons • Example: • C-14 and C-12 • H-1, H-2, and H-3 • Radioisotope – Isotope that is unstable and undergoes decay, thus giving off radiation

  13. PARTICLE LOCATION CHARGE MASS Proton nucleus  + 1 amu Neutron nucleus 0 1 amu  Electron Outside nucleus  - 0.00054 amu  Subatomic Particles

  14. Symbol Name Protons (Atomic Number) Neutrons Mass Number Electrons 73Li  Lithium -7  3   4 7  3  146 C Carbon-14   6 8  14 6 6731Ga Gallium -67 31  36 67  31  Common Isotopes Isotopes of Particular interest – C-14 used in radiocarbon dating I-131 used in thyroid cancer treatment U-235 used in nuclear power

  15. ISOTOPES IN NATURE Atomic Mass -Weighted Average mass of all existing isotopes of an element  Can be calculated by: (percent isotope 1)(molar mass isotopes 1) + (percent isotopes 2)(molar mass isotope 2) +…..Try this with your grades as an example….Final grades will be determined by giving homework 10%, labs 30%, and tests 60%…Homework grade = 85% Lab grade = 80% Test grade = 60% Final grade = (.10)(.85) + (.30)(.80) + (.60)(.60) = .69 

  16. Nuclear Section B Introduction Approx. 90 known naturally occurring elements Approx. 350 known isotopes in our solar system Approx. 70 of these radioactive Radioactive – just means unstable – it naturally decays Approx. 1,600 Lab created isotopes There is a rather constant level of natural radiation in our environment – called background radiation

  17. Type Symbol Change in Atomic Number Change in Neutrons Change in Mass Number Alpha  -2 -2  -4  Beta   +1  -1 0  Gamma   0 0  0  TABLE OF CHANGES RESULTING FROM NUCLEAR DECAY

  18. Spontaneous Radioactive Stability • Production of an particle • Production of a  particle • Production of  rays • Spontaneous Fission

  19. 1. production of a particle

  20. 2. production of b particle

  21. 3. production of g rays

  22. 4. Spontaneous Fission

  23. DECAY SERIES Shows the nuclear decay steps that occur when a radioactive isotope decays to a final stable product

  24. II. Nuclear Fission

  25. Sub-Critical Critical Supercritical

  26. then radioactive decomposition: ½ life = 1.3 sec

  27. then radioactive decomposition: ½ life = 1.3 sec

  28. then radioactive decomposition: ½ life 18.3 months

  29. then radioactive decomposition: ½ life 18.3 months

  30. Other Types of Nuclear Reactions K-capture: the capture of an electron from the first or K shell

  31. 207 207 Other Types of Nuclear Reactions Positron (0+1b): a positive electron

  32. Formation of a Neutron An electron and proton combine to form a neutron. 0-1e + 11p --> 10n

  33. Less mass more protons fewer protons

  34. III. Nuclear Fusion Example #1 • Requires 40,000,000 K to overcome electrostatic repulsion

  35. Half life SM x (1/2)n = EM (1/2)n = EM / SM or EM / SM = (1/2)n n Log (1/2) = Log (EM / SM) n = Log (EM / SM) / Log (1/2) n = t / t1/2 life

  36. ln (N/No) = ln (1/2)n ln (N/No) = - kt t1/2life k = ln (1/2) = 0.693 t1/2life = 0.693/k A = kN

  37. thus, N/Not = - kN1 where N = amount [conc or counts] and k = rate constant  dN/dt = - kN

  38. Half-life : time when

  39. Half-life

  40. Binding Energy energy released during degradation of a nucleus

  41. E = mc2 Energy = mass x speed of light2 1 gram of mass = 9 x 1013 joules = amount of energy needed to power your house for 1,000 years

  42. E = mc2 or E = c2m where c = 3.00 x 108 m/sec

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