topic 12 nuclear chemistry courtesy i. markic. nuclear chemistry rev. 11/19/08 2 nuclear chemistry...

Download Topic 12 Nuclear Chemistry Courtesy I. Markic. Nuclear Chemistry rev. 11/19/08 2 Nuclear Chemistry The study of nuclear reactions and their uses in chemistry

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  • Slide 1
  • Topic 12 Nuclear Chemistry Courtesy I. Markic
  • Slide 2
  • Nuclear Chemistry rev. 11/19/08 2 Nuclear Chemistry The study of nuclear reactions and their uses in chemistry spontaneouslyWhen nuclei change spontaneously, emitting radiation, they are said to be radioactive
  • Slide 3
  • Nuclear Chemistry rev. 11/19/08 3 Radioactive elements are used in medicine as i.diagnostic tools ii.treatment for cancer iii.determine mechanisms for chemical reactions iv.trace movements of atoms in biological systems Radioactive elements are used in archeology To date important historical artifacts Uses of nuclear reactions i.generate electricity ii.create WMDs of property and/or life
  • Slide 4
  • Nuclear Chemistry rev. 11/19/08 4 Radioactivity Radioactive nuclei are called radionuclides Atoms containing radioactive nuclei are called radioisotopes Atoms with the same atomic number but different mass numbers are called isotopes Different isotopes of an element are distinguished by their mass numbers Different nuclei have different stabilities The nuclear properties of an atom depend on the ratio of neutrons to protons in its nucleus
  • Slide 5
  • Nuclear Chemistry rev. 11/19/08 5 Types of Radioactive Decay The most common types 1. alpha decay 2 He 4 2. beta decay -1 e 0 or -1 0 3. gamma radiation 0 0 or just
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  • Nuclear Chemistry rev. 11/19/08 6 + Battery -
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  • Nuclear Chemistry rev. 11/19/08 7
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  • 8 Alpha Radiation 2 He 4 Contains 2 protons and 2 neutrons Has heavy mass, does not travel far| stopped by a thin sheet of paper or skin Dangerous if ingested 92 U 238 90 Th 234 + 2 He 4 emission 92 U 238 + 2 He 4 94 Pu 242 absorption
  • Slide 9
  • Nuclear Chemistry rev. 11/19/08 9 Beta Radiation -1 e 0 or -1 0 Less charge than alpha particle Extremely small mass More penetrating, can pass through paper stopped by aluminum foil or thin pieces of wood 6 C 14 7 N 14 + -1 e 0 emission 19 K 42 + -1 e 0 18 Ar 42 absorption
  • Slide 10
  • Nuclear Chemistry rev. 11/19/08 10 Gamma Radiation 0 0 or just No mass, no charge High energy photon Often emitted with or particles during decay Can pass though paper, wood, and our bodies Can mostly be stopped by several meters of concrete or several cm of lead 90 Th 230 86 Ra 222 + 2 2 He 4 + 0 0
  • Slide 11
  • Nuclear Chemistry rev. 11/19/08 11
  • Slide 12
  • Nuclear Chemistry rev. 11/19/08 12
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  • Nuclear Chemistry rev. 11/19/08 13 Nuclear Transformations There are ~115 different elements, but more than 1500 different nuclei are known (Wait a minutehow is this possible?) Only 264 nuclei are stable and do not decay over time Stability of a nucleus depends on it neutron-to-proton ratio The stable nuclei are in a region called the band of stability
  • Slide 14
  • Nuclear Chemistry rev. 11/19/08 14 As the at # increases, the 0 n 1 : 1 p 1 ratio of the stable nuclei increases The stable nuclei are located in the belt of stability (shaded ) Radioactive nuclei occur outside this belt 2:1 neutron-to- proton ratio
  • Slide 15
  • Nuclear Chemistry rev. 11/19/08 15 n/p too large beta decay X n/p too small positron decay or electron capture Y n/p too large => need more 1 p 1 s &/or fewer 0 n 1 s; so turn 0 n 1 s into 1 p 1 s by n/p too small => need fewer 1 p 1 s &/or more 0 n 1 s; so turn 1 p 1 s into 0 n 1 s by
  • Slide 16
  • Nuclear Chemistry rev. 11/19/08 16 Nuclear Stability Certain numbers of 0 n 1 s and 1 p 1 s are extra stable 0 n 1 or 1 p 1 count = 2, 8, 20, 50, 82, 126 Like extra stable numbers of -1 e 0 s in noble gases (2, 10, 18, 36, 54, 86) Nuclei with even numbers of both 1 p 1 s and 0 n 1 s are more stable than those with odd numbers All isotopes with at#s 84 (Po) are radioactive All isotopes of 43 Tc and 61 Pm are radioactive
  • Slide 17
  • Nuclear Chemistry rev. 11/19/08 17 Transmutation Reactions Transmutation - the conversion of an atom of one element into an atom of a different element Can occur by radioactive decay Can occur when particles ( 1 p 1 -s, 0 n 1 -s, or 2 He 4 -s) bombard the nucleus of an atom 7 N 15 + 1 H 1 6 C 12 + 2 He 4 92 U 238 + 0 n 1 93 Np 239 + -1 0 4 Be 9 + 2 He 4 6 C 12 + 0 n 1
  • Slide 18
  • Nuclear Chemistry rev. 11/19/08 18 Nuclear Transmutation
  • Slide 19
  • Nuclear Chemistry rev. 11/19/08 19 Sample Exercise What product is formed when radium-226 undergoes alpha decay? What element undergoes alpha decay to form lead-208? 12 Mg 27 decays by beta emission to form 1 H 3 __ + -1 e 0 3 Li 9 4 Be 9 + __
  • Slide 20
  • Nuclear Chemistry rev. 11/19/08 20 Sample Exercise 6 C 14 -1 e 0 + ____ 95 Am 241 2 He 4 + ____ 7 N 16 6 O 16 + ____ Alpha decay of francium-208 Beta emission by argon-37 Positron emission by fluorine-17
  • Slide 21
  • Nuclear Chemistry rev. 11/19/08 21 Sample Exercise 3 Li 6 + 0 n 1 2 He 4 + __ 92 U 235 + 0 n 1 __ + 56 Ba 141 + 3 0 n 1 13 Al 27 + 2 He 4 __ + -1 e 0 92 U 235 38 Sr 90 + __ + 0 n 1 + 4 -1 e 0 83 Bi 214 2 He 4 + __ 14 Si 27 -1 e 0 + __ 29 Cu 66 30 Zn 66 + __
  • Slide 22
  • Nuclear Chemistry rev. 11/19/08 22 Decay Series
  • Slide 23
  • Nuclear Chemistry rev. 11/19/08 23 Half-Life (t ) The time required for one-half of the nuclei of a radioisotope sample to decay to products After each half-life, one-half of the atoms we had at the beginning of the half-life have decayed into atoms of a new element
  • Slide 24
  • Nuclear Chemistry rev. 11/19/08 24
  • Slide 25
  • Nuclear Chemistry rev. 11/19/08 25 Fig. 23.3
  • Slide 26
  • Nuclear Chemistry rev. 11/19/08 26 Decay of a 10.0 g Sample of Sr-90
  • Slide 27
  • Nuclear Chemistry rev. 11/19/08 27 Decay of a 1.000 mg Sample of Mo-99
  • Slide 28
  • Nuclear Chemistry rev. 11/19/08 28 Brigham Young Researcher Scott Woodward Taking a Bone Sample
  • Slide 29
  • Nuclear Chemistry rev. 11/19/08 29 A Dendrochronologist Cutting a Section from a Dead Tree
  • Slide 30
  • Nuclear Chemistry rev. 11/19/08 30
  • Slide 31
  • Nuclear Chemistry rev. 11/19/08 31 Sample Exercise Po-214 has a relatively short t of 164 sec. How many seconds would it take for 8.0 g of this isotope to decay to 0.25 g? How many days does it take for 16 g of Pa-107 to decay to 1.0g? t of Pa-107 is 17 days.
  • Slide 32
  • Nuclear Chemistry rev. 11/19/08 32 Sample Exercise In 5.49 seconds, 1.20 g of Ar-35 decay to leave only 0.15 g. What is t of Ar-35? Na-24 has a t of 15 hours. How much Na-24 remains in an 18.0 g sample after 60 hours?
  • Slide 33
  • Nuclear Chemistry rev. 11/19/08 33 In 6.20 h, a 100. g sample of Ag-112 decays to 25.0 g. What is t of Ag-112? Mn-56 is a emitter with t of 2.6 h. What is the mass of Mn-56 in a 1.0 mg sample of the isotope at the end of 10.4 h? C-14 emits beta radiation and decays with t of 5730 years. Assume you start with 2.00 x 10 -12 g C-14. How long is 3 t s? How many grams of the isotope remain at the end of 3 t s? Sample Exercise
  • Slide 34
  • Nuclear Chemistry rev. 11/19/08 34 Nuclear Fission Occurs when the nuclei of certain isotopes are bombarded with neutrons and the nucleus splits into smaller fragments In a chain reaction, some of the neutrons produced react with other fissionable atoms, producing more neutrons with will react with still more fissionable atoms Can release enormous amounts of energy (atomic bombs, nuclear reactors) Exothermic processes Undergoes fission when struck by a slow-moving neutron U-235 or Pu-239
  • Slide 35
  • Nuclear Chemistry rev. 11/19/08 35 Fig. 23.6
  • Slide 36
  • Nuclear Chemistry rev. 11/19/08 36 Fission
  • Slide 37
  • Nuclear Chemistry rev. 11/19/08 37 Uranium Oxide (refined uranium)
  • Slide 38
  • Nuclear Chemistry rev. 11/19/08 38 A PHYSICIST WORKS WITH A SMALL CYCLOTRON AT THE UNIVERSITY OF CALIFORNIA BERKLEY
  • Slide 39
  • Nuclear Chemistry rev. 11/19/08 39
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  • Nuclear Chemistry rev. 11/19/08 40 An Aerial View of the Fermilab High Energy Particle Accelerator
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  • Nuclear Chemistry rev. 11/19/08 41 The Accelerator Tunnel at Fermilab
  • Slide 42
  • Nuclear Chemistry rev. 11/19/08 42 Chain Reaction If the fission process continues and the energy is unchecked, the result is a violent explosion The sample of fissionable material must have a minimum critical mass if not, 0 n 1 -s escape from the sample before they strike another nucleus and cause additional fission The chain R x stops if enough 0 n 1 -s are lost
  • Slide 43
  • Nuclear Chemistry rev. 11/19/08 43 Critical Mass The amount of fissionable material large enough to maintain the chain reaction with a constant rate of fission When critical mass is present, only one 0 n 1 from each fission is subsequently effective in producing another fission
  • Slide 44
  • Nuclear Chemistry rev. 11/19/08 44
  • Slide 45