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Ch. 25- Nuclear Chemistry (originally ch. 18 from old textbook)

Ch. 25- Nuclear Chemistry (originally ch. 18 from old textbook). 25.1 Nuclear Radiation 25.2 Nuclear Transformations 25.3 Fission and Fusion of Atomic Nuclei 25.4 Radiation in Your Life. Diablo Canyon Nuclear Power Plant San Luis Obispo, CA (192 miles south of Cupertino).

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Ch. 25- Nuclear Chemistry (originally ch. 18 from old textbook)

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  1. Ch. 25- Nuclear Chemistry (originally ch. 18 from old textbook) 25.1 Nuclear Radiation 25.2 Nuclear Transformations 25.3 Fission and Fusion of Atomic Nuclei 25.4 Radiation in Your Life Diablo Canyon Nuclear Power Plant San Luis Obispo, CA (192 miles south of Cupertino) Marvel Comics’ “The Incredible Hulk” was created in 1962 by Stan Lee and artist Jack Kirby. The Hulk’s powers began when nuclear scientist Dr. Bruce Banner was accidentally bombarded with gamma rays from a "gamma bomb" he had invented. To properly view this presentation on the web, use the navigation arrows below andleft-click on each page to view any animations.

  2. Chemical reaction vs. Nuclear reaction Chemical reactions: • Atoms attain stable isotopes by losing or sharing electrons • Reactions affected by changes in temperature, pressure, or the presence of catalysts Nuclear chemistry: the chemistry of radioactive substances; study of the atomic nucleus, including fission and fusion and their products Nuclear reactions:* The nuclei of unstable isotopes gain stability by undergoing changes* The changes are accompanied by emission of large amounts of energy

  3. Symbol 25 12 Mg Atomic Review • Atomic number = • Every atom of an element has the same atomic number because the # p defines the element. # of p+ • Mass number (or atomic mass) = • The # n may vary without changing the element. sum of p+ & n X • Atomic notation: Mass # Atomic # Ex: magnesium atom with 13 n =

  4. 5 2 1 1 13 6 1 1 13 6 5 2 He 2 3 H 1 0 C 67 H C He Practice Fill in the blanks:

  5. + + Four Forces in the Nucleus Repulsive: 1. Electrostatic: between p+ (like charges repel) Attractive: 2. “Strong force”: between p+ 3. “Weak force”: between p+ and n 4. Gravity: between all particles Strong > electrostatic > weak > gravity

  6. 25.1 Nuclear Radiation Marie Curie was a Polish scientist whose research led to many discoveries about radiation and radioactive elements. In 1934 she died from leukemia caused by her long-term exposure to radiation. You will learn about the various types of radiation and their effects.

  7. Natural Radioactivity * Discovered in 1895 by Antoine Henri Becquerel, who observed that a uranium salt produced an image on photographic film—thought the film had to be exposed to sunlight, but the plates fogged in a drawer. * The term radioactivity was coined in 1898 by Marie Curie, a Polish physicist, who was doing research with her husband Pierre. (They did much of the initial work on radioactivity, and eventually died of radiation-related illnesses.) Radioactivity: spontaneous emission of particles and/or energy from the nucleus of an atom Radioactive decay: process in which a radioactive atom disintegrates into a different element

  8. Radioactivity How does an unstable nucleus release energy? • Marie Curie (1867-1934) and Pierre Curie (1859-1906) were able to show that rays emitted by uranium atoms caused fogging in photographic plates. • Marie Curie named the process by which materials give off such rays radioactivity. • The penetrating rays and particles emitted by a radioactive source are called radiation.

  9. 25.1 Radioactivity Nuclear reactions differ from chemical reactions in a number of important ways. • In chemical reactions, atoms tend to attain stable electron configurations by losing or sharing electrons. • In nuclear reactions, the nuclei of unstable isotopes, called radioisotopes, gain stability by undergoing changes. • An unstable nucleus releases energy by emitting radiation during the process of radioactive decay.

  10. 25.1 Types of Radiation The three main types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation.

  11. Types of Radioactive Decay

  12. 240 4 Pu + He 94 2 Alpha decay Example: 236 U 92

  13. 240 4 Pu + He 94 2 Alpha decay Example: 236 U 92

  14. 1 137 0 0 n Cs + e + e 55 0 -1 -1 Beta decay • Ex: 137 Ba 56 1 p 1 (One of Cs’s neutrons converts to a proton and electron.) Beta decay animation: http://ie.lbl.gov/education/glossary/AnimatedDecays/Beta-Decay.html

  15. Gamma ray emission • Ex: Pu* (energized) → Pu (stable)

  16. 25.1 Types of Radiation Gamma Radiation A high-energy photon emitted by a radioisotope is called a gamma ray. The high-energy photons are electromagnetic radiation. Radium

  17. 25.1 Types of Radiation

  18. 25.1 Section Quiz. 1. Certain elements are radioactive because their atoms have a) more neutrons than electrons. b) an unstable nucleus. c) a large nucleus. d) more neutrons than protons.

  19. 25.1 Section Quiz. 2. An unstable nucleus releases energy by a) emitting radiation. b) thermal vibrations. c) a chemical reaction. d) giving off heat.

  20. 25.1 Section Quiz. 3. Which property does NOT describe an alpha particle? a) 2+ charge b) a relatively large mass c) a negative charge d) low penetrating power

  21. 25.1 Section Quiz. 4. When a radioactive nucleus releases a high-speed electron, the process can be described as a) oxidation. b) alpha emission. c) beta emission. d) gamma radiation.

  22. 25.2 Nuclear Transformations Radon-222 is a radioactive isotope that is present naturally in the soil in some areas. It has a constant rate of decay. You will learn about decay rates of radioactive substances.

  23. Nuclear Stability and Decay What determines the type of decay a radioisotope undergoes? • The nuclear force is an attractive force that acts between all nuclear particles that are extremely close together, such as protons and neutrons in a nucleus • At these short distances, the nuclear force dominates over electromagnetic repulsions and hold the nucleus together. • More than 1,500 different nuclei are known. Of those, only 264 are stable and do not decay or change with time. These nuclei are in a region called the band of stability.

  24. 25.2 Nuclear Stability and Decay • The neutron-to-proton ratio determines the type of decay that occurs. • A positron is a particle with the mass of an electron but a positive charge. During positron emission, a proton changes to a neutron. • Positron emission is a byproduct of a type of radioactive decay known as beta plus decay. In the process of beta plus decay, an unstable balance of neutrons and protons in the nucleus of an atom triggers the conversion of an excess proton into a neutron. Wisegeek.com

  25. Unstable Atoms * Stable, naturally occurring isotopes • If # of neutrons is too high or too low, the nucleus becomes unstable and emits energy. 1

  26. *Transmutation • Conversion of one element into another that is the result of radioactive decay. Artificial transmutation: • First accomplished by Rutherford in 1919, even though alchemists tried for hundreds of years. • Transmutation of lead into gold was achieved by Glenn Seaborg, who succeeded in transmuting a small quantity of lead in 1980. He also first isolated plutonium for the atomic bomb and discovered/”created” many elements. (NY Times, Feb 1999) • There is an earlier report (1972) in which Soviet physicists at a nuclear research facility in Siberia accidentally discovered a reaction for turning lead into gold when they found the lead shielding of an experimental reactor had changed to gold. • Accomplished with particle accelerators

  27. Transmutation Reactions What are two ways that transmutation can occur? The conversion of an atom of one element to an atom of another element is called transmutation. • Transmutation can occur by radioactive decay. Transmutation can also occur when particles bombard the nucleus of an atom.

  28. Transmutation Reactions The first artificial transmutation reaction involved bombarding nitrogen gas with alpha particles.

  29. Transmutation Reactions The elements in the periodic table with atomic numbers above 92, the atomic number of uranium, are called the transuranium elements. • All transuranium elements undergo transmutation. • None of the transuranium elements occur in nature, and all of them are radioactive. • Transuranium elements are synthesized in nuclear reactors and nuclear accelerators.

  30. Atomic Number & Symbol Mass Number *Disintegration Series • “Heavy” atoms (greater than Bismuth, #83) naturally decay to smaller atoms along a consistent path, or series, of decays. Radioactive U-238→ Th-234 + a Th-234 → Pa-234 + b Pa-234→ U-234 + b U-234→ Th-230 + a Th-230 → Ra-226 + a Ra-226 → Rn-222 + a Rn-222 → Po-218 + a Po-218 → Pb-214 + a Pb-214 → Bi-214 + b Bi-214 → Po-214 + b Po-214 → Pb-210 + a Pb-210 → Bi-210 + b Bi-210→ Po-210 + b Po-210 → Stable Pb-206 + a Source: http://www.frontiernet.net/~jlkeefer/uranium.html

  31. *Radiocarbon (C-14) dating Basic assumptions: • CO2 in the atmosphere contains about 0.00000000010% C-14; this level is held constant through the decay of N-14 to form C-14 which happens in the upper atmosphere. • Plants consume CO2 during photosynthesis and animals eat the plants, so they contain the same C-14:C-12 ratio as long as they are alive. • When an organism dies, the amount of C-12 does not change, but the C-14 content diminishes as it decays. The half-life of C-14 is 5668 years. • By comparing the C-14:C-12 ratio in an artifact to the same ratio in living plants, the age of the artifact can be estimated. • Discovered at University of Chicago in 1949 by Dr. W.F. Libby and his colleagues.

  32. The accuracy of the method has been validated by comparison testing of artifacts with independently known ages, such as those of ancient Egypt and old redwood trees. Limitations: • C-14 dating has a limit of about 70,000 years. Beyond that, the % of C-14 remaining is too small to accurately calculate the age. • However, other radiometric dating methods exist, including: Rb-87 : Strontium 87 (half-life of 48.8 billion years) Th-232 : Pb-208 (half-life of 14.0 billion years) U-238 : Pb-206 (half-life of 4.5 billion years) K-40 : Ar-40 (half-life of 1.3 billion years) • The formation of our solar system (and thus the Earth) has been estimated at 4.5 - 5.0 billion years. • It is also estimated that our universe is between 15-20 billion years old. Sources: http://www.geology.sdsu.edu/visualgeology/geology101/lab6time.htm http://www.dc.peachnet.edu/~pgore/geology/geo102/radio.htm http://superstringtheory.com/cosmo/cosmo1.html

  33. Half-Life After each half-life, half of the existing radioactive atoms have decayed into atoms of a new element. • A half-life (t1/2) is the time required for one-half of the nuclei of a radioisotope sample to decay to products.

  34. Half Life Ex: • Phosphorus-32 radioactively decays to form Sulfur-32 • Half life 32P = 14 days

  35. Half-Life • The ratio of Carbon-14 to stable carbon in the remains of an organism changes in a predictable way that enables the archaeologist to obtain an estimate of its age.

  36. 25.2 Section Quiz. 1. During nuclear decay, if the atomic number decreases by one but the mass number is unchanged, the radiation emitted is a) a positron. b) an alpha particle. c) a neutron. d) a proton.

  37. 25.2 Section Quiz. 2. When potassium-40 (atomic number 19) decays into calcium-40 (atomic number 20), the process can be described as a) positron emission. b) alpha emission. c) beta emission. d) electron capture.

  38. 25.2 Section Quiz. 3. If there were 128 grams of radioactive material initially, what mass remains after four half-lives? a) 4 grams b) 32 grams c) 16 grams d) 8 grams

  39. 25.2 Section Quiz. 4. When transmutation occurs, the ________ always changes. a) number of electrons b) mass number c) atomic number d) number of neutrons

  40. 25.2 Section Quiz 5. Transmutation occurs by radioactive decay and also by a) extreme heating. b) chemical reaction. c) high intensity electrical discharge. d) particle bombardment of the nucleus.

  41. 25.3 Fission and Fusion of Atomic Nuclei The sun is not actually burning. If the energy given off by the sun were the product of a combustion reaction, the sun would have burned out approximately 2000 years after it was formed, long before today. You will learn how energy is produced in the sun.

  42. 1 235 139 94 1 n + Ba + Kr + 3 n + energy U 0 92 56 36 0 Nuclear Fission • Fission: process in which the nucleus of a large, radioactive atom splits into 2 or more smaller nuclei • Caused by a collision with an energetic neutron. • *A neutron is absorbed by a U-235 nucleus. The nucleus is now less stable than before. It then splits into 2 parts and energy is released. Several neutrons are also produced; they may go on to strike the nuclei of other atoms causing further fissions in a process calledsupercriticality. Fission animation: http://www.howstuffworks.com/nuclear-bomb3.htm

  43. *The process of neutron capture and nucleus splitting happens very quickly (takes about 1 x 10-12 seconds). • An incredible amount of energy is released: • As heat and gamma radiation • Because the product atoms and neutrons weigh less than the original U-235 atom; the “missing mass“ has been converted to energy by E=mc2

  44. 25.3 Nuclear Fission What happens in a nuclear chain reaction? When the nuclei of certain isotopes are bombarded with neutrons, they undergo fission, the splitting of a nucleus into smaller fragments. In a chain reaction, some of the neutrons produced react with other fissionable atoms, producing more neutrons which react with still more fissionable atoms.

  45. Mass-Energy Relationship • Einstein's theory of relativity states that energy and mass are related by the speed of light (c) squared. E = mc2 • Can be used to calculate the energy liberated when the “missing mass” (between reactants & products) is known. • * The energy that can be released from 2 kg of highly enriched U-235 (as used in a nuclear bomb) is roughly equal to the combustion of a million gallons of gasoline. 2 kg of U-235 is smaller than a baseball; a million gallons of gasoline would fill approximately 220 tanker trucks.

  46. Nuclear Fission A Nuclear Power Plant • Neutron absorption is a process that decreases the number of slow-moving neutrons. Control rods, made of a material such a cadmium, are used to absorb neutrons. • Neutron moderation is a process that slows down neutrons so the reactor fuel (uranium-235 or plutonium-239) captures them to continue the chain reaction.

  47. *Harnessing Fission: A nuclear power plant Check out: http://science.howstuffworks.com/nuclear-power1.htm • Nuclear power plants utilize the energy released in a controlled fission reaction in the core to heat water in one pipe. • The heat then vaporizes water in another pipe. • The steam drives a turbine and generates electricity. • The steam is in a closed circuit that is never exposed any radiation. • The speed of the fission chain reaction is regulated using carbon control rods which can absorb extra neutrons.

  48. 25.3 Nuclear Waste Why are spent fuel rods from a nuclear reaction stored in water? • Water cools the spent rods, and also acts as a radiation shield to reduce the radiation levels.

  49. *Nuclear Power • The United States currently imports over 58% of its oil supply. There is a need to develop alternative energy sources, such as nuclear, wind, geothermal, solar, … • By 2020 it is expected to be 67%. • At present about 20% of the electrical energy used in the U.S. is generated from power plants using uranium. In France the percentage is 75% .

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