nuclear - Chemistry I Chapter 25 Chemistry I Honors...

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Unformatted text preview: Chemistry I – Chapter 25 Chemistry I Honors – Chemistry Chapter 19 ICP – Chapter 18 ICP 1 Nuclear Chemistry SAVE PAPER AND INK!!! When you print out the notes on PowerPoint, print "Handouts" instead of "Slides" in the print setup. Also, turn off the backgrounds (Tools>Options>Print>UNcheck Radioactivity 2 • One of the pieces of evidence for the One fact that atoms are made of smaller particles came from the work of particles ________ (1876-1934). (1876-1934). • She discovered ________, the ________ the spontaneous disintegration of some elements into smaller pieces. elements Nuclear Reactions vs. Nuclear Normal Chemical Changes Normal 3 • Nuclear reactions involve the nucleus • The nucleus opens, and protons and The neutrons are rearranged neutrons • The opening of the nucleus releases a The tremendous amount of energy that holds the nucleus together – called binding energy energy • “Normal” Chemical Reactions involve Normal” electrons, not protons and neutrons electrons Mass Defect • Some of the mass can be converted into Some energy energy • Shown by a very famous equation! 2 E=mc Energy Mass Speed of light 4 5 Types of Radiation • Alpha (ά) – a positively Alpha positively charged helium isotope - we charged 4 2 He usually ignore the charge because it involves electrons, not protons and neutrons electrons, •Beta (β) – an electron •Gamma (γ – pure energy; ) pure called a ray rather than a particle particle 0 −1 0 0 e γ 6 Other Nuclear Particles • Neutron Neutron 1 0 n • Positron – a positive electron electron 0 +1 e •Proton – usually referred to Proton as hydrogen-1 as •Any other elemental isotope 1 1 H 7 Penetrating Ability 8 Balancing Nuclear Reactions •In the reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation) Atomic numbers must balance and Mass numbers must balance •Use a particle or isotope to fill in the missing protons and neutrons 9 Nuclear Reactions • Alpha emission Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2. Nucleons (nuclear particles… protons and neutrons) are rearranged but conserved 10 Nuclear Reactions • Beta emission Note that mass number (A) is unchanged and atomic number (Z) goes up by 1. 11 Other Types of Nuclear Reactions Positron (0+1β ): a positive electron 207 Electron capture: the capture of an electron Electron 207 12 Learning Check What radioactive isotope is produced in the following bombardment of boron? 10 B 5 + 4He 2 ?+ 1 n 0 13 Write Nuclear Equations! Write the nuclear equation for the beta emitter Co-60. 14 Artificial Nuclear Reactions New elements or new isotopes of known elements New are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4He He 11 and 11B. Reactions using neutrons are called Reactions γ reactions because a γ ray is usually emitted. emitted. Radioisotopes used in medicine are often made by Radioisotopes γ reactions. 15 Artificial Nuclear Reactions Example of a γ Example reaction is production 31 of radioactive 31P for use in studies of P for uptake in the body. uptake 31 15 P+ 1 0 n ---> ---> P+γ 32 32 15 Transuranium Elements Elements beyond 92 (transuranium) made Elements (transuranium) starting with an γ reaction 238 238 92 U+ n ---> ---> 239 239 92 ---> 239 239 93 239 92 U 239 239 93 U+γ 1 0 Np ---> Np Np + 0-1β Np 239 239 94 Pu + Pu β 0 -1 16 Nuclear Fission 17 Nuclear Fission 18 Fission is the splitting of atoms These are usually very large, so that they are not as stable Fission chain has three general steps: 1. Initiation. Reaction of a single atom starts the Initiation. 235 chain (e.g., 235U + neutron) 2. Propagation. Propagation 236 236 U fission releases neutrons that fission initiate other fissions initiate 3. ___________ . 3. 19 Stability Stability of Nuclei of • Out of > 300 stable isotopes: N Even Odd Even 157 52 Odd 50 5 Z 19 9 F 31 15 P 2 H, 63Li, 105B, 147N, 18073Ta H, Li, 10 B, 14 N, 180 1 Band of Stability Band and Radioactive Decay Decay 20 Representation of a fission process. 21 Nuclear Fission & POWER • Currently about 103 Currently nuclear power plants in the U.S. and about 435 worldwide. worldwide. • 17% of the world’s 17% energy comes from nuclear. nuclear. 22 Figure 19.6: Diagram of a nuclear power plant. 23 24 Nuclear Fusion Fusion small nuclei combine 2 H 1 3 + 4 H 1 1 He 2 + n+ 0 Occurs in the sun and other stars Energy 25 Nuclear Fusion Fusion • Excessive heat can not be contained • Attempts at “cold” fusion have FAILED. • “Hot” fusion is difficult to contain 26 Half-Life • HALF-LIFE is the time that it takes for 1/2 a sample to decompose. sample • The rate of a nuclear transformation The depends only on the “reactant” concentration. concentration. Half-Life 27 15 Decay of 20.0 mg of 15O. What remains after 3 half-lives? Decay O. After 5 half-lives? After 28 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 29 Learning Check! The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours? Effects of Radiation 30 31 Geiger Counter • Used to detect radioactive substances 32 Radiocarbon Dating 33 Radioactive C-14 is formed in the upper atmosphere Radioactive by nuclear reactions initiated by neutrons in cosmic radiation cosmic 14 N + 1on ---> 14C + 1H ---> 14 The C-14 is oxidized to CO2, which circulates which through the biosphere. through When a plant dies, the C-14 is not replenished. But the C-14 continues to decay with t1/2 = 5730 years. years. Activity of a sample can be used to date the sample. Nuclear Medicine: Imaging Thyroid imaging using Tc-99m 34 35 Food Irradiation •Food can be irradiated with γ rays from Food 60 60Co or 137Cs. Co 137 •Irradiated milk has a shelf life of 3 mo. Irradiated without refrigeration. without •USDA has approved irradiation of meats USDA and eggs. and ...
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