Nuclear Chemistry The study of the structure of
- Slides: 44
Nuclear Chemistry • The study of the structure of atomic nuclei and the changes they undergo.
Guiding Questions Is radiation dangerous? Is nuclear power a good choice? What is nuclear energy? Are nuclear energy and nuclear bombs both dangerous?
Radioactive Decay • Discovered by Antoine Henri Becquerel in 1896 – He saw that photographic plates developed bright spots when exposed to uranium metals
© 2003 John Wiley and Sons Publishers Figure 4. 1
As you may recall, isotopes are atoms of the same element that have different numbers of neutrons. Isotopes of atoms with unstable nuclei are called radioisotopes
Radioactive Isotopes Stable Isotopes -Atoms that do not release protons or neutrons from the nucleus and ARE NOT RADIOACTIVE. Unstable Isotopes - Atoms that spontaneously release protons and neutrons from its nucleus. These isotopes ARE RADIOACTIVE.
Band of Stability • The region on a graph which indicates all stable nuclei when the number of neutrons are compared to the number of protons for all stable nuclei
Nuclear Reactions • Nuclear reactions are different from chemical reactions Chemical Mass is Reactions conserved (doesn’t change) Nuclear Small Reactions changes in mass Small energy changes Huge energy changes No changes in the nuclei; involve ONLY valance electrons protons, neutrons, electrons and gamma rays can be lost or gained
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
Types of Radiation • The effect of an electric field on three types of radiation is shown. • Positively charged alpha particles are deflected toward the negatively charged plate.
© 2003 John Wiley and Sons Publishers Figure 4. 2: The penetrating power of radiation.
Products of Natural Radioactivity Particle* Alpha Beta Gamma Symbol 4 a 2 0 b -1 0 g 0 Charge 2+ Mass Number Identity 4 Helium nucleus 1 - 0 Electron 0 0 Proton of light *Sometimes a stream of any of these types of particles is called a ray, as in gamma ray,
© 2003 John Wiley and Sons Publishers Figure 4. 4: The components of α rays, β rays, and γ rays.
Types of radioactive decay • alpha particle emission – loss of a helium nucleus.
Types of radioactive decay Beta decay, Nuclear changes that accompany the emission of a beta particle.
b particle emission
particle emission • Gamma rays are high-energy (short wavelength) electromagnetic radiation. They are denoted by the symbol. • As you can see from the symbol, both the subscript and superscript are zero. • Thus, the emission of gamma rays does not change the atomic number or mass number of a nucleus. • Gamma rays almost always accompany alpha and beta radiation, as they account for most of the energy loss that occurs as a nucleus decays.
Induced Nuclear Reactions • Scientists can also force ( = induce) nuclear reactions by smashing nuclei with alpha, beta and gamma radiation to make the nuclei unstable or
BALANCING NUCLEAR EQUATIONS 1. 2. The sums of mass numbers (left superscripts) on each side must be equal. The sums of atomic numbers or nuclear charges (left subscripts) on each side of the equation must be equal. Examples: 238 U 92 4 He 2 214 Pb 82 0 b -1 + + 234 Th 90 214 Bi 83
Balancing Nuclear Equations Complete the following nuclear equations: 1. 2. 3. 217 At 85 231 Th 90 208 Tl 81 213 Bi 83 0 b -1 4 He + ? 2 + ? 0 b -1 231 Pa 91 + ? 208 Pb 82
Nuclear Reactions • Two types: – Fission = the splitting of nuclei – Fusion = the joining of nuclei (they fuse together) • Both reactions involve extremely large amounts of energy Albert Einstein’s equation E = mc 2 illustrates the energy found in even small amounts of matter
Nuclear Fission: • Is the splitting of one heavy nucleus into two or more smaller nuclei, as well as some sub-atomic particles and energy. • A heavy nucleus is usually unstable, due to many positive protons pushing apart. • When fission occurs: 1. Energy is produced. 2. More neutrons are given off.
Nuclear Fission • Neutrons are used to make nuclei unstable – It is much easier to crash a neutral neutron than a positive proton into a nucleus to release energy.
Nuclear Fission Complete the following nuclear equations: (a) 238 U + 1 n (b) 9 Be + 1 H (c) 9 Be + 4 He 239 U 6 Li + ? 12 C + ?
Fission produces a chain reaction
Nuclear Fusion • joining of two light nuclei into one heavier nucleus. – In the core of the Sun, two hydrogen nuclei join under tremendous heat and pressure to form a helium nucleus. – When the helium atom is formed, huge amounts of energy are released. The fusion of hydroge n nuclei
• Scientists cannot yet find a safe, and manageable method to harness the energy of nuclear fusion. – “cold fusion” would occur at temperatures and pressures that could be controlled (but we haven’t figured out how to get it to happen)
Nuclear Fusion Complete the following nuclear equations, thought to be the source of the energy of some stars. (a) 1 H + 12 C ? 13 C + ? (b) 13 N (c) 13 C + 1 H ? (d) 1 H + 14 N ? 15 N + ? (e) 15 O 12 C + ? (f) 15 N + 1 H
Applications • Medicine – – – • Agriculture – – • Chemotherapy Power pacemakers Diagnostic tracers Irradiate food Pesticide Energy – – Fission Fusion
© 2003 John Wiley and Sons Publishers Courtesy Robert Maass/Corbis Images X-ray examination of luggage at a security station.
Food Irradiation • Food can be irradiated with g rays from 60 Co or 137 Cs. • Irradiated milk has a shelf life of 3 mo. without refrigeration. • USDA has approved irradiation of meats and eggs.
© 2003 John Wiley and Sons Publishers Courtesy Custom Medical Stock Photo An image of a thyroid gland obtained through the use of radioactive iodine.
© 2003 John Wiley and Sons Publishers Courtesy CNRI/Phototake Images of human lungs obtained from a γ-ray scan.
© 2003 John Wiley and Sons Publishers Courtesy Kelley Culpepper/Transparencies, Inc. A cancer patient receiving radiation therapy.
© 2003 John Wiley and Sons Publishers Courtesy Scott Camazine/Photo Researchers The world’s first atomic explosion, July 16, 1945 at Alamogordo, New Mexico.
© 2003 John Wiley and Sons Publishers Courtesy Shigeo Hayashi Remains of a building after the explosion of the uranium bomb at Hiroshima, August 6, 1945.
© 2003 John Wiley and Sons Publishers Courtesy David Bartruff/Corbis Images Cooling towers of a nuclear power plant.
© 2003 John Wiley and Sons Publishers Courtesy Sipa Press The nuclear power plant at Chernobyl, after the accident of April 16, 1986.
Challenges of Nuclear Power • Disposal of waste products
Challenges of Nuclear Power » Disposal of waste products • Hazardous wastes produced by nuclear reactions are problematic. – Some waste products, like fuel rods, can be re-used – Some products are very radioactive, and must be stored away from living things. • Most of this waste is buried underground, or stored in concrete • It takes 20 half-lives (thousands of years) before the material is safe.
© 2003 John Wiley and Sons Publishers Courtesy Yucca Mountain Project Construction of a tunnel that will be used for burial of radioactive wastes deep within Yucca Mountain, Nevada.
© 2003 John Wiley and Sons Publishers Courtesy Matthew Neal Mc. Vay/Stone/Getty Images Disposal of radioactive wastes by burial in a shallow pit.
© 2003 John Wiley and Sons Publishers Courtesy AP/Wide World Photos Albert Einstein, he discovered the equation that relates mass and energy.
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