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CHEM 5013 Applied Chemical Principles Chapter Fourteen Professor Bensley Alfred State College

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Chapter Objectives Write, balance, and interpret equations for simple nuclear reactions Write, balance, and interpret equations for simple nuclear reactions Define and distinguish among various modes of nuclear decay, including alpha decay, beta decay, positron emission, and electron capture. Define and distinguish among various modes of nuclear decay, including alpha decay, beta decay, positron emission, and electron capture. Interpret the kinetics of radioactive decay using first-order rate equations Interpret the kinetics of radioactive decay using first-order rate equations

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Review What is a What is a proton? neutron? electron? isotope? What is mass number? atomic number? What is a nuclide symbol?

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Radioactive Decay Radioisotopes: Radioisotopes: Radioactive decay: Radioactive decay:

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Types of Radiation Ernest Rutherford’s Experiments Ernest Rutherford’s Experiments

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Types of Radiation Alpha Particles ( α ) = Helium nucleus Alpha Particles ( α ) = Helium nucleus Beta Particles ( β ) = Electron Beta Particles ( β ) = Electron Positron ( β + ) Positron ( β + ) Gamma Rays ( γ ) Gamma Rays ( γ )

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Nuclear Reactions Alpha decay – decreases mass and atomic number Alpha decay – decreases mass and atomic number Example: 238 U Example: 238 U Beta Decay – no change in mass, increases atomic number – huh?? Beta Decay – no change in mass, increases atomic number – huh?? Converts a neutron to a proton Converts a neutron to a proton

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Nuclear Reactions Gamma Decay – HIGH energy emission (10 8 ) kJ/mol Gamma Decay – HIGH energy emission (10 8 ) kJ/mol Electron Capture – converts a proton to a neutron – no change in mass, decreases atomic number Electron Capture – converts a proton to a neutron – no change in mass, decreases atomic number

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Nuclear Reactions Positron Emission – What happens when a positron collides with an electron? Positron Emission – What happens when a positron collides with an electron? No change in mass, decreases atomic number No change in mass, decreases atomic numberExamples: 1. Complete the following equations with the correct particles and identify the type of reaction shown. 20 O ? + 0 β + ν? 232 U + 4 He 201 Pb 201 Bi + ? 2. Write the equation for the electron capture by 138 La. +1

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Kinetics of Radioactive Decay Kinetics: Kinetics: Activity of a sample = Activity of a sample = SI Unit of rate of decay = SI Unit of rate of decay =

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Kinetics of Radioactive Decay N = N 0 e –kT/ τ Rearrange to get: Radiocarbon Dating - Examine ratio of 14 C to 12 C I living or once living organisms.

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Examples 137 Cs has a half-life of 30.2 years. How long will it take (in years) for a 100.0 g sample to decay to 0.01g? 137 Cs has a half-life of 30.2 years. How long will it take (in years) for a 100.0 g sample to decay to 0.01g? A piece of spear handle is found in an archaeological dig in Central America. It is found to contain 12.5% the level of 14 C as a tree living today. How old is the spear handle? A piece of spear handle is found in an archaeological dig in Central America. It is found to contain 12.5% the level of 14 C as a tree living today. How old is the spear handle?

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