Nuclear Chemistry. Chapter 18

Transcription

1 Nuclear Chemistry Chapter 18

2 AP Chemistry Nuclear Requirements Types of nuclear decay Nuclear Stability Half-life Mass Defect and Binding Energy Topic Appearance on Exam: 3/75 Questions Occasionally in FR

3 Radioactivity Discovered by Antoine Henri Becquerel in 1896 He saw that photographic plates developed bright spots when exposed to uranium metals

4 The Experiment That Started it All They were studying effect of U- salts that were exposed to sunlight and fogged photographic film. On a cloudy day, he left uranium on the film and it made this image. Marie Curie and Antoine Becquerel-1896

5 Definitions Radioactivity - Process by which substances give off energy rays or particles. Radiation - What the actual rays are called. Radioisotopes - Unstable isotopes that become stable by emitting energy and radiation.

6 Marie Sklodowska Curie Shared Physics Nobel Prize 1903 with her husband and Becquerel for Radiation Phenomenon Chemistry Nobel Prize 1911 Discovery of Po and Ra.

7

8 Misunderstood Radiation

9 Misunderstood Radiation

10 The Radium Girls Grace Fryer and the other women at the radium factory in Orange, New Jersey, naturally supposed that they were not being poisoned. It was a little strange, Fryer said, that when she blew her nose, her handkerchief glowed in the dark. But everyone knew the stuff was harmless. The women even painted their nails and their teeth to surprise their boyfriends when the lights went out. They all had a good laugh, then got back to work, painting a glow-in-the-dark radium compound on the dials of watches, clocks, altimeters and other instruments.

11 Chemical vs. Nuclear Reactions Chemical Reactions Occur when bonds are broken Nuclear Reactions Occur when nuclei emit particles and/or rays

12 Chemical vs. Nuclear Reactions Chemical Reactions Occur when bonds are broken Atoms remain unchanged, although they may be rearranged Nuclear Reactions Occur when nuclei emit particles and/or rays Atoms often converted into atoms of another element

13 Chemical vs. Nuclear Reactions Chemical Reactions Occur when bonds are broken Atoms remain unchanged, although they may be rearranged Involve only valence electrons Nuclear Reactions Occur when nuclei emit particles and/or rays Atoms often converted into atoms of another element May involve protons, neutrons, and electrons

14 Chemical vs. Nuclear Reactions Chemical Reactions Occur when bonds are broken Atoms remain unchanged, although they may be rearranged Involve only valence electrons Associated with small energy changes Nuclear Reactions Occur when nuclei emit particles and/or rays Atoms often converted into atoms of another element May involve protons, neutrons, and electrons Associated with large energy changes

15 Chemical vs. Nuclear Reactions Chemical Reactions Occur when bonds are broken Atoms remain unchanged, although they may be rearranged Involve only valence electrons Associated with small energy changes Reaction rate influenced by temperature, particle size, concentration, etc. Nuclear Reactions Occur when nuclei emit particles and/or rays Atoms often converted into atoms of another element May involve protons, neutrons, and electrons Associated with large energy changes Reaction rate is not influenced by temperature, particle size, concentration, etc.

16 Review of Atomic Structure Nucleus 99.9% of the mass 1/10,000 the size of the atom Electrons 0.01% of the mass

17 Review of Atomic Structure Nucleus 99.9% of the mass 1/10,000 the size of the atom Composed of protons (p + ) and neutrons (n 0 ) Electrons 0.01% of the mass Composed of electrons (e - )

18 Review of Atomic Structure Nucleus 99.9% of the mass 1/10,000 the size of the atom Composed of protons (p + ) and neutrons (n 0 ) Positively charged Electrons 0.01% of the mass Composed of electrons (e - ) Negatively charged

19 Review of Atomic Structure Nucleus 99.9% of the mass 1/10,000 the size of the atom Composed of protons (p + ) and neutrons (n 0 ) Positively charged Strong nuclear force (holds the nucleus together) Electrons 0.01% of the mass Composed of electrons (e - ) Negatively charged Weak electrostatic force (because they are charged negatively

20 Three Main Types of Radiation Alpha Beta Gamma

21 Alpha Radiation Loss of an -particle (a helium nucleus) 4 He U Th He

22 Alpha Radiation Alpha radiation occurs when an unstable nucleus emits a particle composed of 2 protons and 2 neutrons. The atom giving up the alpha particle has its atomic number reduced by two. Of course, this results in the atom becoming a different element. For example, Rn undergoes alpha decay to Po.

23 Beta Radiation Beta Decay Loss of a -particle (a high energy electron) 0 1 or 0 1 e 1 0n 1 p I 131 Xe e

24 Beta Radiation Beta radiation occurs when an unstable nucleus emits an electron. As the emission occurs, a neutron turns into a proton.

25 Gamma Radiation Loss of a -ray (high-energy radiation that almost always accompanies the loss of a nuclear particle) 0 0

26 Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Mass Number Atomic Number A Z X Element Symbol proton 1 1 p or 1 1 H neutron 1 0 n electron 0 e -1 or 0-1 positron 0 e +1 or 0 +1 particle 4 He 2 or 4 2 A Z

27 Penetrating Ability

28 Geiger-Müller Counter

29 Geiger Counter Used to detect radioactive substances

30 Balancing Nuclear Equations 1. Conserve mass number (A). The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants. 235 U 1 0 n 92 + Cs Rb 1 n = (2 x 1) 2. Conserve atomic number (Z) or nuclear charge. The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants. 235 U 1 0 n 92 + Cs Rb 1 n = (2 x 0)

31 212 Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212 Po. alpha particle - 4 He 2 or Po 4 He + A X 84 2 Z 212 = 4 + A A = = 2 + Z Z = Po 4 He Pb

32 Beta decay Nuclear Stability and Radioactive Decay 14 C 14 N n K 40 Ca n Decrease # of neutrons by 1 Increase # of protons by 1 1 n 1 p n Positron decay 11 C 11 B n K 38 Ar n Increase # of neutrons by 1 Decrease # of protons by 1 1 p 1 n n n and n have A = 0 and Z = 0

33 Nuclear Stability and Radioactive Decay Electron capture decay 37 Ar + 0 e 37 Cl + n Fe + 0 e 55 Mn + n Increase # of neutrons by 1 Decrease # of protons by 1 Alpha decay 1 p + 0 e 1 n + n Po 4 He Pb Decrease # of neutrons by 2 Decrease # of protons by 2 Spontaneous fission 252 Cf In n

34 Learning Check What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He? + 1 n 5 2 0

35 Learning Check What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He 13 N + 1 n

36 Write Nuclear Equations! Write the nuclear equation for the beta emitter Co Co 0 e + 60 Ni

37 Artificial Nuclear Reactions: Transmutation 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. Reactions using neutrons are called reactions because a ray is usually emitted. Radioisotopes used in medicine are often made by reactions.

38 Artificial Nuclear Reactions Example of a reaction is production of radioactive 31 P for use in studies of P uptake in the body P + 1 0n ---> 32 15P +

39 Transuranium Elements Elements beyond 92 (transuranium) made starting with an reaction U + 1 0n ---> U U ---> Np Np ---> Pu + 0-1

40 Nuclear Stability Certain numbers of neutrons and protons are extra stable n or p = 2, 8, 20, 50, 82 and 126 Similar to extra stable numbers of electrons in noble gases (e - = 2, 10, 18, 36, 54 and 86) Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protons All isotopes of the elements with atomic numbers higher than 83 are radioactive All isotopes of Tc and Pm are radioactive 23.2

41 Zone of Stability and Radioactive Decay Radioisotopes lying outside the zone will undergo spontaneous decay until located within the zone!

42 Half-Life (Kinetics) HALF-LIFE is the time that it takes for 1/2 a sample to decompose. The rate of a nuclear transformation depends only on the reactant concentration.

43 Half-Life Decay of 20.0 mg of 15 O. What remains after 3 halflives? After 5 half-lives?

44 Kinetics of Radioactive Decay For each duration (half-life), one half of the substance decomposes. For example: Ra-234 has a half-life of 3.6 days If you start with 50 grams of Ra-234 After 3.6 days > 25 grams After 7.2 days > 12.5 grams After 10.8 days > 6.25 grams

45 Kinetics of Radioactive Decay A rate = - DA Dt A = A 0 e (-kt) daughter lna = lna 0 - kt A = the amount of atoms at time t A 0 = the amount of atoms at time t = 0 k is the decay constant (sometimes called l) t Ln 2 ½ = t = k ½ k

46 Carbon Dating (no not for Prom)

47 In case you missed the boat

48 Carbon-14 Cycle t 1 / 2 for 14 C is 5730 years

49 Our recent trip to LA for WOF a side trip to the La Brea Tar Pits!

50 Radio Carbon Dating

51 Iceman Ötzi On 19 September 1991 an extraordinary archaeological discovery was made at a high-altitude mountain pass of the Ötztal Alps near the Austrian-Italian border. Two alpine mountaineers discovered a body partially frozen in a melting glacier.

52 Iceman Ötzi

53 Iceman Ötzi

54 14 C dating of the Iceman Accelerator mass spectrometry (AMS) measurements of 14C in bone and tissue of the Iceman Ötzi revealed that the approximate date of death was 4550 years ago. The carbon-14 in living tissue has a disintegration rate of 13.6 counts per minute.

55 Learning Check! Determine the counts per minute of the 14 C in the tissue of the iceman based on the approximate age of this specimen counts per minute

56 Radiocarbon Dating Carbon-14 and Uranium N + 1 n 14 C + 1 H C 14 N n t ½ = 5,730 years Uranium-238 Dating 238 U Pb t ½ = 4.51 x 10 9 years 14-step decay process here!

57 Learning Check! 1) The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 31 hours? 2) #31 on p. 870

58 Biological Effects of Radiation Radiation absorbed dose (rad) 1 rad = 1 x 10-5 J/g of material Roentgen equivalent for man (rem) 1 rem = 1 rad x Q Quality Factor -ray = 1 = 1 = 20

59 Effects of Radiation

60 Nuclear Radiation

61 Avoidable Radiation! Brain-free zones

62 If you fail to avoid the radiation risk

63 Nuclear Fission Fission involves the splitting of atoms with a very large nucleus. Typically, these are generally not as stable. Fission chain has three general steps: 1. Initiation. Reaction of a single atom starts the chain (e.g., 235 U + neutron) 2. Propagation. 235 U fission releases neutrons that initiate other fissions 3. Termination. Fissile material is exhausted.

64 Nuclear Fission

65 Representation of a fission process.

66 Mass Defect Some of the mass can be converted into energy Shown by a very famous equation! E=mc 2 Energy Mass Speed of light

67 Nuclear Fission 235 U + 1 n 90 Sr Xe n + Energy Energy = [mass 235 U + mass n (mass 90 Sr + mass 143 Xe + 3 x mass n )] x c 2 Energy = 3.3 x J per 235 U = 2.0 x J per mole 235 U Combustion of 1 ton of coal = 5 x 10 7 J

68 Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons. E = mc 2 BE + 19 F 9 1 p n BE = 9 x (p mass) + 10 x (n mass) 19 F mass BE (amu) = 9 x x BE = amu BE = 2.37 x J 1 amu = 1.49 x J Converts amu to kg and multiplies by c 2 binding energy per nucleon = binding energy number of nucleons = 2.37 x J 19 nucleons = 1.25 x J

69 Nuclear binding energy per nucleon vs Mass number This is the energy transition for fission! nuclear binding energy nucleon nuclear stability

70 Nuclear Fission Nuclear chain reaction is a self-sustaining sequence of nuclear fission reactions. The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the critical mass. Non-critical Critical

71 Nuclear Fission Weapons

72 Trinity Site explosion, second after explosion, July 16, Note that the viewed hemisphere's highest point in this image is about 200 meters high

73 Nuclear Fission Weapons

74 Nuclear Fission Weapons

75 Nuclear Fission Weapons

76 Nuclear Fission & POWER Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. (another 71 under construction) 17% of the world s energy comes from nuclear.

77 Diagram of a nuclear power plant

78 The Core of a Reactor

79 Nuclear Fission 35,000 tons SO 2 Annual Waste Production 4.5 x 10 6 tons CO x 10 6 ft 3 ash 70 ft 3 vitrified waste 1,000 MW coal-fired power plant 1,000 MW nuclear power plant

80 Nuclear Accidents Three Mile Island partial meltdown due to lost coolant Chernobyl Fault of operators and testing safety equipment too close to the limit. France safe operation provides 2/3 of power requirements for the country.

81 Chernobyl

82 Chernobyl

83 Chernobyl

84 Chernobyl

85 Chernobyl

86 Chernobyl v=t7jfx2kei_k Seconds From Disaster : Meltdown at Chernobyl - FULL

87 Most Recent Nuclear Disaster

88 Nuclear Fusion Fusion small nuclei combine 2 H + 3 H 4 He + 1 n + Energy Occurs in the sun and other stars

89 Nuclear Fusion Fusion Overcoming electrostatic repulsion Excessive heat is difficult to contain Attempts at cold fusion have FAILED. Hot fusion is currently under intense study!

90 Fusion

91 Fusion Basics

92 Inertial Confinement Fusion

93 Tokamak Fusion Reactor

94 Slightly Uncontrolled Fusion

95 How do we get uncontrolled fusion? VERY CAREFULLY!!!

96 Nuclear binding energy per nucleon vs Mass number Now we are interested in this transition for fusion! nuclear binding energy nucleon nuclear stability

97 Other Military Uses of Uranium Depleted Uranium the fissionable U-235 extracted Due to the high density of U-238 (almost equal to Au or W) Armor Plating Armor Penetrators Special ability of uranium to be self-sharpening and pyrophoric both desirable for killing armor and its crew.

98 Radioisotopes in Medicine 1 out of every 3 hospital patients will undergo a nuclear medicine procedure 24 Na, t ½ = 14.8 hr, emitter, blood-flow tracer 131 I, t ½ = 14.8 hr, emitter, thyroid gland activity 123 I, t ½ = 13.3 hr, -ray emitter, brain imaging 18 F, t ½ = 1.8 hr, + emitter, positron emission tomography 99m Tc, t ½ = 6 hr, -ray emitter, imaging agent Brain images with 123 I-labeled compound

99 Chemistry In Action: Food Irradiation Dosage Up to 100 kilorad kilorads 1000 to 10,000 kilorads Effect Inhibits sprouting of potatoes, onions, garlics. Inactivates trichinae in pork. Kills or prevents insects from reproducing in grains, fruits, and vegetables. Delays spoilage of meat poultry and fish. Reduces salmonella. Extends shelf life of some fruit. Sterilizes meat, poultry and fish. Kills insects and microorganisms in spices and seasoning.