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__________ Isotopes / Atomic Mass and The Periodic Table

CHEM 108. The Nucleus. __________ Isotopes / Atomic Mass and The Periodic Table. Nuclear Decay / Radioactivity. http://chemconnections.org/general/movies/Radioactivity.MOV.

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__________ Isotopes / Atomic Mass and The Periodic Table

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  1. CHEM 108 The Nucleus __________ Isotopes / Atomic Mass and The Periodic Table

  2. Nuclear Decay / Radioactivity http://chemconnections.org/general/movies/Radioactivity.MOV • Unstable nuclei are radioactive. They “decay”, i.e. they emit particles, which lead to different elements and isotopes that can be detected and accurately measured.

  3. http://chemconnections.org/general/movies/radioactivityofeverydayob.movhttp://chemconnections.org/general/movies/radioactivityofeverydayob.mov http://www.pbs.org/video/2209769748/

  4. Radioactive Decay Uranium alpha () decay Fiesta Plate Radium alpha () decay Watch Face Thorium alpha () decayLantern Mantle Lead Shield

  5. Nuclear Particlesemitted from unstable nucleii • Emitted Nuclear Particles: Mass Charge Symbol • alpha particle 4 amu +2 • beta particle very small -1 • gamma very very small 0 positron very small +1

  6. Nuclides http://www.nndc.bnl.gov/chart/

  7. Number of Stable Isotopes (Nuclides) Elements 48 through 54 Atomic Number of Element Number (Z) Stable Nuclides Cd 48 8 In 49 2 Sn 50 10 Sb 51 2 Te 52 8 I 53 1 (37) Xe 54 9 Magic numbers are 2, 8, 20, 28, 50, or 82 protons or neutrons. Even numbers of protons and neutrons are more stable than odd.

  8. Distribution of Stable Nuclides Protons Neutrons Stable Nuclides % • Even Even 157 58.8 • Even Odd 53 19.9 • Odd Even 50 18.7 • Odd Odd 7 2.6 Total = 267 100.0%

  9. QUESTION In alpha decay, the nucleus looses the equivalent of 2 protons and the element’s atomic number (a.n.) is decreased by 2, producing another element whose (a.n.) is 2 less. What is the change in atomic number of a nucleus that results from beta decay? +1 +2 –1 –2 0 • Emitted Particles: • Mass emitted • alpha particle +2 amu • beta particle -1 amu

  10. Nuclear Penetrating Power • alpha particle: low • beta particle: moderate • gamma: high • X-rays: high Water

  11. Nuclear Penetrating Power Human Absorbtion aplastic anemia ""Nothing in life is to be feared; it is only to be understood." and X-rays • Radiation effects are cumulative (Madame Curie: 1867-1934) • rad = radiation absorbed dose ( 0.01 J/kg) • rem= radiation equivalent for man (1 rem = 1 rad x Q; Q=1 for β, γ, X-rays; Q= 3-10 for neutrons; Q=10 for p+; Q= 20 for -particles) • Background radiation = 0.13 rem • Annual exposure limit is set at 0.17 rem above background • Dosimeters measure radiation absorbed

  12. Which type of radioactive emission is the most penetrating? QUESTION • Emitted Particles: • Mass Charge • alpha particle 4 amu +2 • beta particle very small -1 • gamma very very small 0 Alpha Beta Gamma Delta Zeta

  13. Medical X-Rays First Medical X-Ray (1895) Mrs. Element #111’s hand and ring (What’s her name?) Mrs. Wilhelm Röntgen

  14. QUESTION Where does most of our yearly exposure to radiation come from? Nuclear power plants Smoke detectors Medical X-rays Naturally occurring sources Human-made sources

  15. CHEMISTRY of the Atom • Isotopes vary in their relative natural abundance. • Periodic Table’s atomic mass is a weighted average of all isotopic masses • The mass of sodium, Na, element #11 is listed as 22.99 amu. Which isotope is naturally present in the larger amount: the isotope with 12 neutrons or with 13 neutrons? (There is a small percentage of the isotope with 11 neutrons.)

  16. QUESTION Two stable isotopes of an element have isotopic masses of 10.0129 amu and 11.0093 amu. The atomic mass is 10.81. Which isotope is more abundant? A) There is insufficient information to answer the question. B) There are equal amounts of each isotope. C) The isotope with a mass of 10.0129 amu is more abundant. D) The isotope with a mass of 11.0093 amu is more abundant.

  17. CHEMISTRY of AtomsUnstable Isotopes and Time • Carbon’s three Nuclides: Stable Unstable Unstable

  18. CHEMISTRY of AtomsUnstable Isotopes and Time https://en.wikipedia.org/wiki/Radiocarbon_dating • Atomic Number = 6 (atom’s identity) • Carbon-14 • Atomic Mass = 14 (isotope 14) • 6 protons; 8 neutrons = 14 – 6 • 14C : Unstable, beta decay • Half life = 5,730±40 years Accelerator Mass Spectrometer Lawrence Livermore National Laboratory

  19. Radioactive Decay of 14C Over Time https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1960/ The Nobel Prize in Chemistry 1960 was awarded to Willard F. Libby "for his method to use carbon-14 for age determination in archaeology, geology, geophysics, and other branches of science".

  20. QUESTION Which of the following is the best definition of the half-life of a radioactive isotope? The time it takes for 50% of the parent nuclide atoms to decay to the daughter nuclide atoms The time it takes for a 50% reduction in radioactivity The lifetime of a radioactive sample The time it takes for 25% of the parent nuclide atoms to decay to the daughter nuclide atoms The time it takes for 100% of the parent nuclide atoms to decay to the daughter nuclide atoms

  21. QUESTION Based solely on the following half-lives, which radioactive atom in the list is the most radioactive, that is, decays the fastest? 14CCarbon-14 (5730 yrs) 226Ra Radium-226 (1620 yrs) 238U Uranium-238 (4.5 million yrs) 214Po Polonium-214 (1.6 ms) 32P Phosphorus-32 (14 days)

  22. Radiocarbon Dating for Determiningthe Age of Artefacts Ground Sloth Dung (Off scale) 

  23. QUESTION An artefact of ground sloth dung was originally thought to have been recently deposited, but on analysis was found to be much older. Based on radio carbon dating, the sample was at the test’s limits (~7 half lives old). How many years old was this sample thought to be? (C-14 half-life is 5730 years.) 5.73 × 103 yr 1.72 × 104 yr 2.29 × 104 yr 2.87 × 104 yr 4.01 × 104 yr

  24. Writing Atomic Symbols (Not Written the Same as in the Periodic Table) 39 K Mass number   Element Symbol 19 Atomic number  39 K Also written as 

  25. CHEMISTRY of the Atom • Atomic Number = 6 (atom’s identity) • Carbon • Atomic Mass = 13 (isotope 13) • 6 protons; # neutrons = 13 - 6 • neutral atom has 6 electrons

  26. CHEMISTRY of the Atom • Atomic Mass of Carbon: • What is the “weighted” atomic mass? 12.00000 x 98.98/100 + 13.00335 x 1.011 = 11.8776 + 0.13146 = 12.0090 12.01

  27. QUESTION

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