Chapter19_LEC

Chapter19_LEC - Chemistry: A Molecular Approach, 1st Ed....

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Chapter 19 Radioactivity and Nuclear Chemistry 2008, Prentice Hall Chemistry: A Molecular Approach , 1 st Ed. Nivaldo Tro Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA
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Tro, Chemistry: A Molecular Approach 2 The Discovery of Radioactivity Antoine-Henri Becquerel designed an experiment to determine if phosphorescent minerals also gave off X-rays
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Tro, Chemistry: A Molecular Approach 3 The Discovery of Radioactivity Becquerel discovered that certain minerals were constantly producing penetrating energy rays he called uranic rays like X-rays but not related to fluorescence Becquerel determined that all the minerals that produced these rays contained uranium the rays were produced even though the mineral was not exposed to outside energy Energy apparently being produced from nothing??
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Tro, Chemistry: A Molecular Approach 4 The Curies Marie Curie used electroscope to detect uranic rays in samples Discovered new elements by detecting their rays radium named for its green phosphorescence polonium named for her homeland Since these rays were no longer just a property of uranium, she renamed it radioactivity
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Tro, Chemistry: A Molecular Approach 5 Electroscope +++ When charged, the metal foils spread apart due to like charge repulsion When exposed to ionizing radiation, the radiation knocks electrons off the air molecules, which jump onto the foils and discharge them, causing them to drop down.
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Tro, Chemistry: A Molecular Approach 6 Other Properties of Radioactivity radioactive rays can ionize matter cause uncharged matter to become charged basis of Geiger Counter and electroscope radioactive rays have high energy radioactive rays can penetrate matter radioactive rays cause phosphorescent chemicals to glow basis of scintillation counter
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Tro, Chemistry: A Molecular Approach 7 Types of Radioactive Rays Rutherford discovered there were three types of radioactivity alpha rays ( α ) have a charge of +2 c.u. and a mass of 4 amu what we now know to be helium nucleus beta rays ( β ) have a charge of -1 c.u. and negligible mass electron-like gamma rays ( γ 29 form of light energy (not particle like α and β )
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Tro, Chemistry: A Molecular Approach 8 Rutherford’s Experiment ++++++++++++ -------------- α γ β
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Tro, Chemistry: A Molecular Approach 9 Penetrating Ability of Radioactive Rays α β γ 0.01 mm 1 mm 100 mm Pieces of Lead
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Tro, Chemistry: A Molecular Approach 10 Facts About the Nucleus Every atom of an element has the same number of protons atomic number ( Z ) Atoms of the same elements can have different numbers of neutrons isotopes different atomic masses Isotopes are identified by their mass number ( A ) mass number = number of protons + neutrons
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Tro, Chemistry: A Molecular Approach 11 Facts About the Nucleus The number of neutrons is calculated by subtracting the atomic number from the mass
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Chapter19_LEC - Chemistry: A Molecular Approach, 1st Ed....

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