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George M. McKelvy, Ph.D.1 Chapter 4 The Structure of the Atom
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George M. McKelvy, Ph.D.2 Section 4.4 Unstable Nuclei and Radioactive Decay
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George M. McKelvy, Ph.D.3 Objectives Explain the relationship between unstable nuclei and radioactive decay. Characterize alpha, beta, and gamma radiation in terms of mass and charge.
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George M. McKelvy, Ph.D.4 Review Vocabulary element: a pure substance that cannot be broken down into simpler substances by physical or chemical means
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George M. McKelvy, Ph.D.5 New Vocabulary radioactivityalpha particle radiationnuclear equation nuclear reactionbeta radiation radioactive decaybeta particle alpha radiationgamma rays
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George M. McKelvy, Ph.D.6 Unstable atomic nuclei emit radiation to gain stability.
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7 Radioactivity Nuclear reactions or decay can change one element into another element. In the late 1890s, scientists noticed some substances spontaneously emitted radiation, a process they called radioactivity. The rays and particles emitted are called radiation. A process that involves a change in an atom’s nucleus is called nuclear reaction or decay.
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George M. McKelvy, Ph.D.8 Radioactive Decay Unstable nuclei lose energy by emitting radiation in a spontaneous process called radioactive decay. Unstable radioactive elements undergo radioactive decay thus forming stable nonradioactive elements.
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9 Radioactive Decay Alpha radiation is made up of positively charged particles called alpha particles. Each alpha particle contains two protons and two neutrons and has a 2+ charge.
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10 Radioactive Decay The figure shown below is a nuclear equation showing the radioactive decay of plutonium-240 to uranium-236.
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11 Radioactive Decay plutonium-240 uranium-236 alpha particle + The mass is conserved in nuclear equations.
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12 Radioactive Decay Beta radiation is radiation that has a negative charge and emits beta particles. Each beta particle is an electron with a 1- charge.
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13 Radioactive Decay potassium-40 calcium-40 beta particle +
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14 Radioactive Decay Alpha, beta, and gamma radiation can be determined by using a magnetic field. Alpha and beta have opposite charges and undergo deflection in opposite directions.
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15 Radioactive Decay Gamma rays are high-energy radiation with no mass and no charge (neutral). Gamma rays account for most of the energy lost during radioactive decay.
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16 Radioactive Decay Table 4.5 Characteristics of Radiation AlphaBetaGammaSymbol or e - or Mass (amu) 41/18400 Mass (kg) 6.65 x 10 -27 9.11 x 10 -31 0 Charge 2+1-0
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17 Radioactive Decay
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George M. McKelvy, Ph.D.18 Radioactive Decay Atoms that contain too many or too few neutrons are unstable and lose energy through radioactive decay to form a stable nucleus. Few exist in nature—most have already decayed to stable forms.
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George M. McKelvy, Ph.D.19 Assessment A reaction that changes one element into another is called what? A. chemical reaction B. beta radiation C. nuclear reaction D. physical reaction
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George M. McKelvy, Ph.D.20 Assessment A reaction that changes one element into another is called what? A. chemical reaction B. beta radiation C. nuclear reaction D. physical reaction
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George M. McKelvy, Ph.D.21 Assessment Why are radioactive elements rare in nature? A. They do not occur on Earth. B. Most have already decayed to a stable form. C. They take a long time to form. D. They afre too hard to detect.
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George M. McKelvy, Ph.D.22 Assessment Why are radioactive elements rare in nature? A. They do not occur on Earth. B. Most have already decayed to a stable form. C. They take a long time to form. D. They afre too hard to detect.
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George M. McKelvy, Ph.D.23
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