Ozone/CFCs

Chapter 24 Nuclear Chemistry24.1 Nuclear Radiation24.2 Radioactive Decay (includes decay rates & radiochemical dating)24.3 Nuclear Reactions (TransmutationPart only)24.4 Applications & Effects of Nuclear Reactions (except for radiation dose and intensity/distance)1

Section 24.1 Nuclear RadiationSummarize the developments that led to the discovery and understanding of nuclear radiation, including the names of the important scientists and the nature and significance of their contributions.Distinguish between chemical and nuclear reactions.Identify alpha, beta, and gamma radiations in terms of composition and key properties.Rank the penetrating power of the various types of radiation.Predict the effect of an electric field on the path of the various types of radiation.Under certain conditions, some nuclei can emit alpha, beta, or gamma radiation.

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Key ConceptsWilhelm Roentgen discovered X rays in 1895.Henri Becquerel, Marie Curie, and Pierre Curie pioneered the fields of radioactivity and nuclear chemistry. Gamma radiation has the most and alpha particles the least penetrating power of the 3 basic types of nuclear radiation.Section 24.1 Nuclear Radiation3Chemical vs Nuclear ReactionsChemicalNuclearBonds broken & formedNuclei emit particles and/or raysAtoms remain unchanged may be rearranged or ionizedAtoms often changed into atoms of new elementInvolve only valence electronsMay involve protons, neutrons, & electronsSmall energy changesLarge energy changes4Chemical vs Nuclear ReactionsChemicalNuclearReaction rate influenced by temperature, pressure, concentration, and catalystsRate not normally affected by temperature, pressure, or catalysts5Classifying Classify each of the following as a chemical reaction, a nuclear reaction, or neither:Thorium emits a beta particleTwo atoms share electrons to form a bondA sample of pure sulfur releases heat as it slowly coolsA piece of iron rustsNuclearChemicalNeitherChemical?6Discovery of RadioactivityWilhelm Roentgen (Germany), 1895: invisible rays emitted when electrons bombarded surface of certain materialsRays caused photographic plates to darkenRoentgen called these high energy rays called X rays Roentgen in 1901 became first Nobel laureate in physics for this discovery

7Becquerel discovered that certain minerals were constantly producing penetrating energy rays he called uranic rays like X-rays, but not related to fluorescenceDetermined that all minerals that produced these rays contained uraniumrays were produced even though mineral was not exposed to outside energyEnergy apparently being produced from nothing??Discovery of Radioactivity99Discovery of RadioactivityHenri Becquereluranium saltK2UO2(SO4)2Darkened photographic plates even when not exposed to light

10Discovery of RadioactivityMarie Curie (Polish born French physicist/chemist) ~ 1896-1898Named process by which materials give off such rays radioactivity Emitted rays and particles she named radiationDeveloped device to measure radioactivity

11Detecting Radiation: Electroscope++++++When positively charged, metalfoils in electroscope spread apart due tolike charge repulsionWhen exposed to ionizing radiation, radiation knocks electrons off air molecules, which jump onto foils and discharge them, causing them todrop down1212Discovery of RadioactivityCuries in 1898, by processing several tons of uranium ore (pitchblende), identified 2 new radioactive elements: polonium, radiumCuries shared 1903 Nobel prize in physics with BecquerelMarie awarded 1911 Nobel prize in chemistry for work with polonium & radiumDied in 1934 from effects of radiation14Discovery of RadioactivityName, DateContributionWilhelm Roentgen, 1895Discovery of X-RaysHenri Becquerel, 1896Uranium salt darkens photographic plateMarie Curie, 1896-1898(up to 1934)Introduced terms radioactivity & radiation; developed device to measure radioactivityPierre & Marie Curie, 1898Isolated polonium and radium & continued study of radiation153 Common Types of RadiationAlpha particlesBeta particlesGamma rays(two more types described in next section)

17Alpha RadiationAlpha particle 42He+2 2 protons & 2 neutrons = nucleus of helium-4 atom +2 charge

+18Beta Radiation0-1b Beta particles fast moving electronsOriginate from decay of a neutron

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neutron

protonBeta Decay In NeutronelectronneutrinoW bosonExample of weak force, of which W is a boson Particle Symbol Relative mass Electron e- 1/1840 Proton p+ 1.000 Neutron n0 1.001Matter changed to energy plus other matterNeutron (made of quarks - fundamental) does not contain an electron (a lepton) Gamma Radiation00g High energy radiation; masslessExcept for very unusual cases, gamma radiation always accompanies alpha and beta decay few pure gamma emitters 21Characteristics of Alpha, Beta, and Gamma Radiation

22Alpha, Beta, Gamma PropertiesParticleEnergyPenetrating Poweralpha~ 5 MeVBlocked by paperbeta0.05 to 1 MeVBlocked by thin metal foil (aluminum foil)gamma~ 1 MeVBlocked only by thick layers of lead or concrete23Penetrating Ability of Radioactive Raysabg0.01 mm 1 mm 100 mmThickness of Lead2424Effect of Electric Field on Trajectory of Subatomic Particles

Lead BlockRadioactive SourceHolePositive plateNegative platea 2+ chargeb 1- chargeg 0 charge25X-RaysNot generated by nuclear processes (get by bombarding materials with electrons)Like gamma rays form of high energy electromagnetic radiation (gamma has higher energy)Both X and gamma rays highly penetrating & can be very damaging to living tissue26PracticeNuclear RadiationProblems 1-5, page 864Problems 34-41, page 894

27Chapter 24 Nuclear Chemistry24.1 Nuclear Radiation24.2 Radioactive Decay (includes decay rates & radiochemical dating)24.3 Nuclear Reactions (TransmutationPart only)24.4 Applications & Effects of Nuclear Reactions (except for radiation dose and intensity/distance)28

Section 24.2 Radioactive DecayExplain why certain nuclei are radioactive while others are stable.Predict the type of radiation an unstable nucleus will emit.Apply your knowledge of radioactive decay to write balanced nuclear equations. Solve problems involving radioactive decay rates.Explain the basis for the technique of radiochemical dating, especially carbon dating.Describe the decay processes of positron emission and electron capture.Unstable nuclei can break apart spontaneously, changing the identity of atoms.

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Key ConceptsRadioisotopes emit radiation to attain more-stable atomic configurations.Atomic number and mass number are conserved in nuclear reactions. Radiochemical dating is a technique for determining the age of an object by measuring the amount of certain radioisotopes remaining in the object.Section 24.2 Radioactive Decay30

Key ConceptsA half-life is the time required for half of the atoms in a radioactive sample to decay. The number of nuclei N remaining after a certain number of half-lives n or after some time t can be calculated from:

Section 24.2 Radioactive Decay31Nuclear ReactionsInvolve a change in atoms nucleusRadioactive materials spontaneously emit radiation Called radioactive decay Do this because a radioactive nucleus is unstableGain stability by losing energy 32Pencil Analogy for StabilityGravitational Potential Energy

33Forces Between Nucleons

Green:Strong Force (attractive)Purple:EM Force (repulsive for protons)34Nuclear Stability - ForcesNucleons (protons, neutrons) held together by strong forceOvercomes electrostatic repulsion by protonsNeutrons dont have repulsionStability tied to neutron/proton ratio (n/p)High atomic number nuclei need relatively more neutrons for stabilityRange for stable nuclei: 1:1 light to 1.5:1 heavy (Pb, AN 82)35Neutron-to-Proton Ratio Shaded region corresponds to band or belt of stability

36Nuclear StabilityRadioactive nuclei are found outside band of stability above/below/beyondUndergo decay to gain stabilityAll elements with atomic number (AN) > 82 (lead) are radioactiveIsotopes of elements with AN 82 but outside band of stability are radioactive37Nuclear Stability Decay SeriesVarious decay types change n/p in different waysUnstable nuclei lose energy through radioactive decay in order to form a nucleus with a stable n/p ratioEventually, radioactive atoms undergo enough decays to form stable atoms Lead-206 is final decay product of Uranium-238 (14 steps)38Decay of 238U to 206Pb

39PracticeNuclear StabilityProblems 12 - 14 page 874Problems 42, 45 48, 50 page 894

40Nuclear Equations

Atomic number (AN) and mass numbers (MN) are shownAtomic and mass numbers are conservedAN: 88 = 86 +2MN: 226 = 222 + 4415 Types of RadiationAlpha BetaPositron Emission *Electron Capture *Gamma

* New in this section42Alpha RadiationAlpha particle emission changes the elementLeaves n/p about the same (for heavier elements)In example below, start with radium, end up with radon

n/p: 138/88=1.57 136/86 =1.5843Beta Radiation0-1b Beta particles fast moving electronsOriginate from decay of neutronBeta emission changes elementLowers n/pIn example below, start with carbon, end up with nitrogen

n/p: 8/6=1.43 7/7 =1.00

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Positron Emission (+ Decay)4545Positron Emission (+ Decay)+++++++++Neutron-deficient isotopes can decay by proton decay (emitting positrons antiparticle of electron)+anti-neutrinopositronNet effect: one proton replaced by

neutron anti-neutrino positron46Electron CaptureLike positron emission, also reduces number of protons (increase n/p)Nucleus draws in surrounding electron (usually from lowest energy level)Electron combines with proton to form neutron with X-ray emission11p + 0-1e 10n + X-ray 8137Rb + 0-1e 8136Kr + X-ray47Decay Processes that Increase n/pPositron Emission

Electron Capture

+48Particle Changes Positron Emission: proton neutron

Electron Capture: proton neutron

Beta Emission: neutron proton

4949Decay Process SummaryDecayParticleMass # ChangeAN Changealpha42He-4-2beta0-10+1Positron Emission010-1Electron CaptureX-Ray Photon0-1gamma000050Nuclear Equations

Atomic number (AN) and mass numbers (MN) are shownAtomic and mass numbers are conservedAN: 88 = 86 +2MN: 226 = 222 + 451Nuclear Equations6027Co 6028Ni + ?Conserve mass number: 60 = 60 + 0Conserve atomic number: 27 = 28 + (-1) Particle must be 0-1b24195Am 23793Np + ?Conserve mass number: 241 = 237 + 4Conserve atomic number: 95 = 93 +2Particle must be 42He52Practice: Write Nuclear equation for each of FollowingAlpha emission from U-238Beta emission from Ne-24Positron emission from N-13Electron capture by Be-7

5353PracticeWriting & Balancing Nuclear EquationsProblems 6 - 8 page 869Problems 51 - 54, page 89454Half Life Time for of radioisotope in sample to undergo nuclear decayHalf life remains constantIn 7 half lives,