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NUCLEAR CHEMISTRY. Discovery of Radiation. Roentgen (1895). Studied fluorescent materials that glowed when hit with a beam of electrons. - PowerPoint PPT Presentation

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  • NUCLEAR CHEMISTRY

  • Discovery of Radiation

    Roentgen (1895) Discovered a mysterious form of radiation was given off even without electron beam. This radiation could pass through paper and other objects but not dense materials (lead, bone).Called them X-raysStudied fluorescent materials that glowed when hit with a beam of electrons.

  • Becquerel (1896)Studied fluorescent minerals containing uranium.Discovered radioactivity by accident on a cloudy day:Thought that an external source was needed to produce the mysterious radiation.Found that uranium emits radiation without external source.

  • Thought radioactivity was a property of heavy elements.Pierre and Marie CurieDuring study, discovered new radioactive elements: Polonium and Radium.Wondered how small mass can give off large amount of energy:Explained by Einstein with E=mc2.

  • Studied radioactivity and named types of nuclear radiation.RutherfordDiscovered that elements decay into other elements after emitting nuclear radiation. Called it Nuclear Decay.Gold foil experiment revealed that the mass of an atom is concentrated in the nucleus (atom is mostly space)

  • Atomic StructureRecall:Atoms consist of a positively charged nucleus, which has protons and neutrons.42169283259181461272101214238210 4Isotope atoms of the same chemical element that have a different number of neutrons. Each isotope of a given element is designated by the total number of its protons plus its neutrons.

    IsotopeSymbol# protons# neutronsAtomic MassMo-101H-2C-14U-238Bi-210He-4

  • Nuclear Forces

    Electric repulsion ________ charge particles repel each other

    same

    Strong Nuclear Force causes protons and neutrons to ________ each other

    attract

    Stable Nuclei = strong nuclear force is ________ than repulsion force

    greater

    Unstable Nuclei = strong nuclear force is ________ than repulsion force

    Have too many or too few neutrons in nucleusHave more than 83 protons in nucleusWill undergo radioactive decay to form a more stable nucleus

    less

  • Nuclear DecayWhy nuclides decayneed stable ratio of neutrons to protonsTransmutation-One element becomes another.More than 83 protons means that the nuclei is unstable (radioactive)

  • Types of RadiationAlpha particle ()helium nucleuspaper2+Beta particle (-)electron1-leadPositron (+)positron1+Gamma ()high-energy photon0concreteChargeShielding

  • Penetrating Ability of Radiation

  • Alpha EmissionNumbers must balance!!occurs when the nucleus has too many protons which cause excessive repulsion.

  • Alpha EmissionEx. Plutonium-239 undergoes alpha decay+239Atomic Mass:=2354+94Atomic #:=922+Masses must be equal = Conservation of mass

  • Ex. Polonium-210 undergoes alpha decay to produce this daughter nuclide+Alpha EmissionAtomic Mass:Atomic #:=

  • Beta Emissionoccurs when the neutron to proton ratio is too great.

  • Ex. Polonium-210 undergoes beta decay to produce this daughter nuclide+Beta EmissionAtomic Mass:Atomic #:=

  • Positron EmissionOccurs when the neutron to proton ratio is too small.

  • Ex. Polonium-210 undergoes positron emission to produce this daughter nuclide+Positron EmissionAtomic Mass:Atomic #:=

  • Electron Captureoccurs when the neutron to proton ratio in the nucleus is too small.

  • Ex. Polonium-210 captures an electron to produce this daughter nuclide+Electron CaptureAtomic Mass:Atomic #:=

  • Gamma Emission

    Emission of high energy electromagnetic wave.occurs when the nucleus is at too high an energy.

  • Ex. Polonium-210 undergoes gamma decay to produce this daughter nuclide+Gamma EmissionAtomic Mass:Atomic #:=

  • Write Nuclear Equations!Write the nuclear equation for the beta emitter Co-60.