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1 © 2006 Brooks/Cole - Thomson Chemistry and Chemical Reactivity 6th Edition John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 23 Nuclear Chemistry.

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Presentation on theme: "1 © 2006 Brooks/Cole - Thomson Chemistry and Chemical Reactivity 6th Edition John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 23 Nuclear Chemistry."— Presentation transcript:

1 1 © 2006 Brooks/Cole - Thomson Chemistry and Chemical Reactivity 6th Edition John C. Kotz Paul M. Treichel Gabriela C. Weaver CHAPTER 23 Nuclear Chemistry © 2006 Brooks/Cole Thomson Lectures written by John Kotz

2 2 © 2006 Brooks/Cole - Thomson Nuclear Chemistry Pictures of human heart before and after stress using gamma rays from radioactive Tc-99m

3 3 © 2006 Brooks/Cole - Thomson Why do you care? PET scans Nuclear Power Space travel Smoke Detectors (Am-241) Ionizing Radiation and X-rays Neutron Activation Exposure (pilots, nuclear accidents, Radon) Carbon Dating Nuclear Weapons

4 4 © 2006 Brooks/Cole - Thomson Nuclear Radiation The Process of emitting energy in the form of waves or particles. Comes from the Nucleus of the Atom –The Neutrons –Instability – Binding Energy –E=mc 2 –Non-conservation of Mass

5 5 © 2006 Brooks/Cole - Thomson ATOMIC COMPOSITION ProtonsProtons –positive electrical charge –mass = x g –relative mass = atomic mass units (amu) ElectronsElectrons – negative electrical charge –relative mass = amu NeutronsNeutrons –no electrical charge –mass = x g –relative mass = amu

6 6 © 2006 Brooks/Cole - Thomson Isotopes Atoms of the same element (same Z) but different mass number (A).Atoms of the same element (same Z) but different mass number (A). Boron-10 ( 10 B) has 5 p and 5 n: 10 5 BBoron-10 ( 10 B) has 5 p and 5 n: 10 5 B Boron-11 ( 11 B) has 5 p and 6 n: 11 5 BBoron-11 ( 11 B) has 5 p and 6 n: 11 5 B 10 B 11 B

7 7 © 2006 Brooks/Cole - Thomson Radioactivity One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ).One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ). She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

8 8 © 2006 Brooks/Cole - Thomson Types of Radiation

9 9 © 2006 Brooks/Cole - Thomson Penetrating Ability

10 10 © 2006 Brooks/Cole - Thomson Nuclear Reactions Alpha emissionAlpha emission Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2. Nucleons are rearranged but conserved

11 11 © 2006 Brooks/Cole - Thomson Nuclear Reactions Beta emissionBeta emission Note that mass number (A) is unchanged and atomic number (Z) goes up by 1. How does this happen?

12 12 © 2006 Brooks/Cole - Thomson Other Types of Nuclear Reactions Positron ( 0 +1 ): a positive electron K-capture: K-capture: the capture of an electron from the first or K shell An electron and proton combine to form a neutron e p --> 1 0 n 207

13 13 © 2006 Brooks/Cole - Thomson Radioactive Decay Series

14 14 © 2006 Brooks/Cole - Thomson Stability of Nuclei Heaviest naturally occurring non- radioactive isotope is 209 Bi with 83 protons and 126 neutrons Heaviest naturally occurring non- radioactive isotope is 209 Bi with 83 protons and 126 neutrons There are 83 x 126 = 10,458 possible isotopes. Why so few actually exist? There are 83 x 126 = 10,458 possible isotopes. Why so few actually exist?

15 15 © 2006 Brooks/Cole - Thomson Stability of Nuclei Up to Z = 20 (Ca), n = p (except for 7 3 Li, 11 5 B, 19 9 F) Up to Z = 20 (Ca), n = p (except for 7 3 Li, 11 5 B, 19 9 F) Beyond Ca, n > p (A > 2 Z) Beyond Ca, n > p (A > 2 Z) Above Bi all isotopes are radioactive. Fission leads to smaller particles, the heavier the nucleus the greater the rate. Above Bi all isotopes are radioactive. Fission leads to smaller particles, the heavier the nucleus the greater the rate. Above Ca: elements of EVEN Z have more isotopes and most stable isotope has EVEN N. Above Ca: elements of EVEN Z have more isotopes and most stable isotope has EVEN N.

16 16 © 2006 Brooks/Cole - Thomson Stability of Nuclei Suggests some PAIRING of NUCLEONS Something inside the nucleus gives each atom a probability of radioactive decay Even Odd Odd Even ZN

17 17 © 2006 Brooks/Cole - Thomson Band of Stability and Radioactive Decay Am --> Np emission reduces Z emission increases Z Co --> Ni Isotopes with low n/p ratio, below band of stability decay, decay by positron emission or electron capture

18 18 © 2006 Brooks/Cole - Thomson Binding Energy, E b E b is the energy required to separate the nucleus of an atom into protons and neutrons. Use E=mc 2 Find the mass of the isotope. Sum the masses of the nucleons. For m, use the DIFFERENCE between those masses.

19 19 © 2006 Brooks/Cole - Thomson Calculate Binding Energy For deuterium, 2 1 H: 2 1 H ---> 1 1 p n Mass of 2 1 H = g/mol Mass of proton = g/mol Mass of neutron = g/mol m = g/mol = 2.39x10 -6 kg/mol c = 3x10 8 m/sec From Einstein s equation: E b = (m)c 2 = 2.15 x J/mol How much binding energy is there per nuclear particle? E b per nucleon = E b /2 nucleons = 1.08 x 10 8 kJ/mol nucleons

20 20 © 2006 Brooks/Cole - Thomson Half-Life HALF-LIFE is the time it takes for 1/2 a sample to disappear.HALF-LIFE is the time it takes for 1/2 a sample to disappear. The rate of a nuclear transformation depends only on the reactant concentration. It does not depend on any factors outside the nucleus.The rate of a nuclear transformation depends only on the reactant concentration. It does not depend on any factors outside the nucleus. Half-life is a property that can be used to identify an element.Half-life is a property that can be used to identify an element. Half-life cannot predict the likelihood a single atom will decayHalf-life cannot predict the likelihood a single atom will decay

21 21 © 2006 Brooks/Cole - Thomson Half-Life Decay of 20.0 mg of 15 O. What remains after 3 half-lives? After 5 half-lives?

22 22 © 2006 Brooks/Cole - Thomson Kinetics of Radioactive Decay Activity (A) = Disintegrations/time N is the number of atoms Decay is first order, and so ln (A/A o ) = -kt or ln (A) – ln (A o ) = -kt The half-life of radioactive decay is t 1/2 = 0.693/k

23 23 © 2006 Brooks/Cole - Thomson Radiocarbon Dating Radioactive C-14 is formed in the upper atmosphere by nuclear reactions initiated by neutrons in cosmic radiation 14 N + 1 o n ---> 14 C + 1 H The C-14 is oxidized to CO 2, which circulates through the biosphere. There is a constant % of C-14 in the atmosphere. While a plant is alive, it has the same % of C-14 in it as the atmosphere. When a plant dies, the C-14 is not replenished. But the C-14 continues to decay with t 1/2 = 5730 years. Activity of a sample can be used to date the sample.

24 24 © 2006 Brooks/Cole - Thomson Radiocarbon Dating

25 25 © 2006 Brooks/Cole - Thomson Man-made Eyes to See Small Things Humans needed to find a way to extend their senses, to gather knowledge about things beyond our physical constraints. Light can be thought of as a piece of information sent between matter. The wavelength/frequency/energy of light determines how it interacts with matter and also predicts where it came from. Certain materials can see light that our eyes cannot. Using these materials we learn about the elements in space and on earth.

26 26 © 2006 Brooks/Cole - Thomson Human Limitations The molecules in our eyes only work within a very specific range of wavelengths.

27 27 © 2006 Brooks/Cole - Thomson Our Sun- Seen by Ultraviolet Light

28 28 © 2006 Brooks/Cole - Thomson Extending Our Vision Common detector materials that interact with light: Sodium Iodide crystal: Plastic scintillator: Germanium Crystal: Silicon:

29 29 © 2006 Brooks/Cole - Thomson Cosmic Rays Super fast particles from the sun and outer space (protons and ions)--- Strike the atmosphere and become pions (positively charged fundamental particle), then muons (heavy electrons). Built a detector to see them using a plastic scintillator.

30 30 © 2006 Brooks/Cole - Thomson Obtainable info: –Direction of radiation –Shielding effects Pyramids example Depth inside Earth –Solar activity levels 200 muons/m 2 /second Proton from sun Pion Molecule in atmosphere Muon Neutrino Atom of Hydrocarbon Light Cosmic Rays Photomultiplier Tube (PMT)

31 31 © 2006 Brooks/Cole - Thomson Cosmic rays are the source of C-14 used in radiocarbon dating!

32 32 © 2006 Brooks/Cole - Thomson Terrestrial Radiation Obtainable info: –Naturally occurring radioactive isotopes can be identified. –Composition of isotopes in rocks is compared to rocks from around the world. –Background radiation in the air can be measured –Investigation of radiation in the ground. Uses gamma ray spectroscopy to see light that comes from matter in the ground

33 33 © 2006 Brooks/Cole - Thomson Summary Certain materials interact with the light that our eyes don t detect. Devices made from these materials have lead to the field of spectroscopy, meaning seeing light. All modern devices convert a light signal into an electrical signal. The electrical signal is arranged in a way that allows us to see what is going on with our eyes.

34 34 © 2006 Brooks/Cole - Thomson Bubble Chambers Alpha, Beta, and Gamma Particles rip through a supercooled gas, ionizing them, and forming bubbles.

35 35 © 2006 Brooks/Cole - Thomson Artificial Nuclear Reactions 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. Radioisotopes used in medicine are often made by these n, reactions.

36 36 © 2006 Brooks/Cole - Thomson Applications: –Test for the presence of heavily shielded dangerous nuclear material. –Create small amounts of elements (alchemy) –Find approximate percent compositions of elements in a substance. Neutron Activation –Shoot neutrons into a substance, stuffing them into a nucleus to make it unstable. They will then decay in a special way that we can see what is in them.

37 37 © 2006 Brooks/Cole - Thomson Transuranium Elements Elements beyond 92 (transuranium) made starting with an n, reaction U n ---> U U n ---> U U ---> Np U ---> Np Np ---> Np Np ---> Np

38 38 © 2006 Brooks/Cole - Thomson Transuranium Elements & Glenn Seaborg 106 Sg

39 39 © 2006 Brooks/Cole - Thomson Nuclear Fission

40 40 © 2006 Brooks/Cole - Thomson Nuclear Fission Fission chain has three general steps: 1. Initiation. Reaction of a single atom starts the chain (e.g., 235 U + neutron) 2. Propagation. 236 U fission releases neutrons that initiate other fissions 3. Termination.

41 41 © 2006 Brooks/Cole - Thomson Nuclear Fission & Lise Meitner 109 Mt

42 42 © 2006 Brooks/Cole - Thomson Nuclear Fission & POWER Currently about 104 nuclear power plants in the U.S. and about 400 worldwide.Currently about 104 nuclear power plants in the U.S. and about 400 worldwide. 17% of the world s energy comes from nuclear fission.17% of the world s energy comes from nuclear fission. What are would be the benefits and drawbacks to using nuclear FUSION instead of nuclear fission?What are would be the benefits and drawbacks to using nuclear FUSION instead of nuclear fission?

43 43 © 2006 Brooks/Cole - Thomson Nuclear Medicine: Imaging

44 44 © 2006 Brooks/Cole - Thomson BNCT Boron Neutron Capture Therapy 10 B isotope (not 11 B) has the ability to capture slow neutrons 10 B isotope (not 11 B) has the ability to capture slow neutrons In BNCT, tumor cells preferentially take up a boron compound, and subsequent irradiation by slow neutrons kills the cells via the energetic 10 B --> 7 Li neutron capture reaction (that produces a photon and an alpha particle)In BNCT, tumor cells preferentially take up a boron compound, and subsequent irradiation by slow neutrons kills the cells via the energetic 10 B --> 7 Li neutron capture reaction (that produces a photon and an alpha particle) 10 B + 1 n ---> 7 Li + 4 He + photon 10 B + 1 n ---> 7 Li + 4 He + photon

45 45 © 2006 Brooks/Cole - Thomson Food Irradiation Food can be irradiated with rays from 60 Co or 137 Cs.Food can be irradiated with rays from 60 Co or 137 Cs. Irradiated milk has a shelf life of 3 mo. without refrigeration.Irradiated milk has a shelf life of 3 mo. without refrigeration. USDA has approved irradiation of meats and eggs.USDA has approved irradiation of meats and eggs.

46 46 © 2006 Brooks/Cole - Thomson Effects of Radiation Rem: Quantifies biological tissue damage Usually use millirem Usually use millirem

47 47 © 2006 Brooks/Cole - Thomson


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