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Chemistry: A Molecular Approach , 2nd Ed. Nivaldo Tro. Chapter 19 Radioactivity and Nuclear Chemistry. Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA. Nuclear Medicine. Changes in the structure of the nucleus are used in many ways in medicine - PowerPoint PPT Presentation

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Chapter 19Radioactivity and Nuclear ChemistryRoy KennedyMassachusetts Bay Community CollegeWellesley Hills, MAChemistry: A Molecular Approach, 2nd Ed.Nivaldo Tro

Copyright 2011 Pearson Education, Inc.1Nuclear MedicineChanges in the structure of the nucleus are used in many ways in medicineNuclear radiation can be used to visualize or test structures in your body to see if they are operating properlye.g. labeling atoms so their intake and output can be monitoredNuclear radiation can also be used to treat diseases because the radiation is ionizing, allowing it to attack unhealthy tissueTro: Chemistry: A Molecular Approach2Copyright 2011 Pearson Education, Inc.

The Discovery of RadioactivityAntoine-Henri Becquerel designed an experiment to determine if phosphorescent minerals also gave off X-raysphosphorescence is the long-lived emission of light by atoms or molecules that sometimes occurs after they absorb lightX-rays are detected by their ability to penetrate matter and expose a photographic plate3Tro: Chemistry: A Molecular Approach

Copyright 2011 Pearson Education, Inc.3The Discovery of Radioactivity4Tro: Chemistry: A Molecular ApproachBecquerel discovered that certain minerals were constantly producing energy rays that could penetrate matterBecquerel determined that 1.all the minerals that produced these rays contained uranium2.the rays were produced even though the mineral was not exposed to outside energyHe called them uranic rays because they were emitted from minerals that contained uraniumlike X-raysbut not related to phosphorescenceEnergy apparently being produced without energy input??Copyright 2011 Pearson Education, Inc.4

The Curies5Tro: Chemistry: A Molecular ApproachMarie Curie broke down these minerals and used an electroscope to detect where the uranic rays were coming fromShe discovered the rays were emitted from specific elementsShe also discovered new elements by detecting their raysradium named for its green phosphorescence polonium named for her homelandBecause these rays were no longer just a property of uranium, she renamed it radioactivityCopyright 2011 Pearson Education, Inc.5Electroscope++++++When charged, the metalfoils spread apart due tolike charge repulsionWhen exposed to ionizing radiation, the radiation knocks electrons off theair molecules, which jump onto the foils and discharge them, allowing them todrop down6Tro: Chemistry: A Molecular ApproachCopyright 2011 Pearson Education, Inc.6Other Properties of Radioactivity7Tro: Chemistry: A Molecular ApproachRadioactive rays can ionize mattercause uncharged matter to become chargedbasis of Geiger Counter and electroscopeRadioactive rays have high energyRadioactive rays can penetrate matterRadioactive rays cause phosphorescent chemicals to glowbasis of scintillation counterCopyright 2011 Pearson Education, Inc.7What Is Radioactivity?Radioactivity is the release of tiny, high-energy particles or gamma rays from an atomParticles are ejected from the nucleus8Tro: Chemistry: A Molecular ApproachCopyright 2011 Pearson Education, Inc.Types of Radioactive Decay9Tro: Chemistry: A Molecular ApproachRutherford discovered three types of raysalpha (a) rays have a charge of +2 c.u. and a mass of 4 amuwhat we now know to be helium nucleusbeta (b) rayshave a charge of 1 c.u. and negligible masselectron-likegamma (g) raysform of light energy (not a particle like a and b)In addition, some unstable nuclei emit positronslike a positively charged electronSome unstable nuclei will undergo electron capturea low energy electron is pulled into the nucleus Copyright 2011 Pearson Education, Inc.9Rutherfords Experiment++++++++++++--------------agb10Tro: Chemistry: A Molecular ApproachCopyright 2011 Pearson Education, Inc.10Penetrating Ability of Radioactive Raysabg0.01 mm 1 mm 100 mmPieces of Lead11Tro: Chemistry: A Molecular ApproachCopyright 2011 Pearson Education, Inc.11Facts About the NucleusVery small volume compared to volume of the atomEssentially entire mass of atomVery denseComposed of protons and neutrons that are tightly held togetherthe particles that make up the nucleus are called nucleons12Tro: Chemistry: A Molecular ApproachCopyright 2011 Pearson Education, Inc.Facts About the NucleusEvery atom of an element has the same number of protonsatomic number (Z)Atoms of the same elements can have different numbers of neutronsisotopesdifferent atomic massesIsotopes are identified by their mass number (A)mass number = number of protons + neutrons13Tro: Chemistry: A Molecular ApproachCopyright 2011 Pearson Education, Inc.13Facts About the NucleusThe number of neutrons is calculated by subtracting the atomic number from the mass numberThe nucleus of an isotope is called a nuclideless than 10% of the known nuclides are non-radioactive, most are radionuclidesEach nuclide is identified by a symbolElement Mass Number = X A14Tro: Chemistry: A Molecular Approach

Copyright 2011 Pearson Education, Inc.14RadioactivityRadioactive nuclei spontaneously decompose into smaller nucleiradioactive decaywe say that radioactive nuclei are unstabledecomposing involves the nuclide emitting a particle and/or energyThe parent nuclide is the nucleus that is undergoing radioactive decay The daughter nuclide is the new nucleus that is madeAll nuclides with 84 or more protons are radioactive

15Tro: Chemistry: A Molecular ApproachCopyright 2011 Pearson Education, Inc.15Important Atomic Symbols16Tro: Chemistry: A Molecular Approach

Copyright 2011 Pearson Education, Inc.16Transmutation17Tro: Chemistry: A Molecular Approach

Rutherford discovered that during the radioactive process, atoms of one element are changed into atoms of a different element transmutationshowing that statement 3 of Daltons Atomic Theory is not valid all the time, only for chemical reactionsFor one element to change into another, the number of protons in the nucleus must change!Copyright 2011 Pearson Education, Inc.17Chemical Processes vs. Nuclear ProcessesChemical reactions involve changes in the electronic structure of the atomatoms gain, lose, or share electronsno change in the nuclei occursNuclear reactions involve changes in the structure of the nucleuswhen the number of protons in the nucleus changes, the atom becomes a different element18Tro: Chemistry: A Molecular ApproachCopyright 2011 Pearson Education, Inc.Nuclear EquationsWe describe nuclear processes with nuclear equationsUse the symbol of the nuclide to represent the nucleus Atomic numbers and mass numbers are conserveduse this fact to predict the daughter nuclide if you know parent and emitted particle19Tro: Chemistry: A Molecular Approach

Copyright 2011 Pearson Education, Inc.19Alpha Emission20Tro: Chemistry: A Molecular Approach

An particle contains 2 protons and 2 neutronshelium nucleusMost ionizing, but least penetrating of the types of radioactivityLoss of an alpha particle meansatomic number decreases by 2mass number decreases by 4

Copyright 2011 Pearson Education, Inc.2021Tro: Chemistry: A Molecular Approach

Copyright 2011 Pearson Education, Inc.21

Beta Emission22Tro: Chemistry: A Molecular Approach

A particle is like an electronmoving much fasterproduced from the nucleusAbout 10 times more penetrating than a, but only about half the ionizing abilityWhen an atom loses a particle itsatomic number increases by 1mass number remains the sameIn beta decay, a neutron changes into a proton

Copyright 2011 Pearson Education, Inc.2223Tro: Chemistry: A Molecular Approach

Copyright 2011 Pearson Education, Inc.23

Gamma Emission24Tro: Chemistry: A Molecular Approach

Gamma (g) rays are high energy photons of lightNo loss of particles from the nucleusNo change in the composition of the nucleussame atomic number and mass numberLeast ionizing, but most penetratingGenerally occurs after the nucleus undergoes some other type of decay and the remaining particles rearrangeCopyright 2011 Pearson Education, Inc.24

Positron Emission25Tro: Chemistry: A Molecular Approach

Positron has a charge of +1 c.u. and negligible massanti-electronSimilar to beta particles in their ionizing and penetrating abilityWhen an atom loses a positron from the nucleus, itsmass number remains the sameatomic number decreases by 1Positrons result from a proton changing into a neutronCopyright 2011 Pearson Education, Inc.2526Tro: Chemistry: A Molecular Approach

Copyright 2011 Pearson Education, Inc.26Electron Capture27Tro: Chemistry: A Molecular Approach

Occurs when an inner orbital electron is pulled into the nucleusNo particle emission, but atom changessame result as positron emissionProton combines with the electron to make a neutronmass number stays the sameatomic number decreases by one

Copyright 2011 Pearson Education, Inc.27Particle Changes28Tro: Chemistry: A Molecular Approach

Copyright 2011 Pearson Education, Inc.2829Tro: Chemistry: A Molecular Approach

Copyright 2011 Pearson Education, Inc.29What Kind of Decay and How Many Protons and Neutrons Are in the Daughter? Alpha emission giving a daughter nuclide withnine protons and seven neutrons11 p+9 n030Tro: Chemistry: A Molecular Approach= proton= neutron? +Copyright 2011 Pearson Education, Inc.? +What Kind of Decay and How Many Protons and Neutrons Are in the Daughter?, Continued Beta emission giving a daughter nuclide with10 protons and 11 neutrons9 p+12 n031Tro: Chemistry: A Molecular Approach= proton= neutron= electronCopyright 2011 Pearson Education, Inc.What Kind of Decay and How Many Protons and Neutrons Are in the Daughter?, Continued Positron emission giving a daughter nuclide withfour protons and five neutrons5 p+4 n032Tro: Chemistry: A Molecular Approach? += proton= neutron= positronCopyright 2011 Pearson Education, Inc.Nuclear

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