Chapter 4 complete - Lecture 29: Radioactivity Goals:...

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Lecture 29: Radioactivity Goals: Describe alpha, beta, positron and gamma radiation. Write equations showing mass numbers and atomic numbers for radioactive decay. Describe the detection and measurement of radiation. Calculate the amount of radioisotope remaining after one or more half-lives Outline (Timberlake 4.1-4.4): Natural Radioactivity (4.1) Nuclear Reactions (4.2) Radiation Measurements (4.3) Half-Life of a Radioisotope (4.4) Problems for Extra Practice: 4.1, 4.3, 4.5, 4.7, 4.9, 4.13, 4.15, 4.17, 4.19, 4.21, 4.23, 4.25, 4.31, 4.33
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Chemical Reactions vs. Nuclear Reactions Chemical reactions Nuclear Reactions Atoms are rearranged by the breaking and forming of chemical bonds Elements (or isotopes of the same elements) are converted from one to another Only electrons in atomic orbitals are involved in the breaking and forming of bonds Protons, neutrons, electrons and other elementary particles may be involved Reactions are accompanied by absorption or release of relatively small amounts of energy Reactions are accompanied by absorption or release of tremendous amounts of energy Rates of reaction are influenced by temperature, pressure, concentration and catalysts Rates of reaction are normally not affected by temperature, pressure and catalysts
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Nuclear Symbol X A Z X = Atomic symbol of the element A = The mass number (protons plus neutrons: A = Z + N ) Z = The atomic number: the number of protons in the nucleus (All atoms of the same element have the same # of protons.) N = The number of neutrons in the nucleus N = A - Z Isotopes = atoms of an element with the same number of protons, but different number of neutrons in the nucleus The Nuclear Symbol of the Atom
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Radioactive Isotopes A radioactive isotope • has an unstable nucleus • emits radiation to become more stable • can be one or more of the isotopes of an element
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Nuclear Radiation Nuclear radiation • is the radiation emitted by an unstable atom • takes the form of alpha particles, neutrons, beta particles, positrons, or gamma rays
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Types of Radiation • Alpha ( ) particle is two protons and two neutrons • Beta ( ) particle is a high-energy electron • Positron ( + ) is a positive electron • Gamma ( ) ray is high-energy released from a nucleus
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Alpha Decay When a radioactive nucleus emits an alpha particle, a new nucleus forms that has • a mass number 4 less than that of the initial nucleus • an atomic number that has decreased by 2 from that of the initial nucleus
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In a completed nuclear equation, the • sum of the mass numbers of the unstable isotope and the products are equal • sum of the atomic numbers of the unstable isotope and the products are equal Sum of Mass Numbers 251 = 251 251 Cf 247 Cm + 4 He 98 96 2 98 = 98 Sum of Atomic Numbers Completing Nuclear Equations
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This note was uploaded on 01/18/2012 for the course CHEM 120A taught by Professor Leahmiller during the Fall '11 term at University of Washington.

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Chapter 4 complete - Lecture 29: Radioactivity Goals:...

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