nuclear chemistry. 10.1 radioactivity radioactivity: process in which an atomic nucleus emits...

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  • Slide 1
  • Nuclear Chemistry
  • Slide 2
  • 10.1 Radioactivity Radioactivity: process in which an atomic nucleus emits charged particles and energy
  • Slide 3
  • Radioisotope: any atom containing an unstable nucleus
  • Slide 4
  • During nuclear decay, atoms of one element can change into atoms of a different element altogether Uranium 238 decays into Thorium 234 (also a radioisotope)
  • Slide 5
  • Nuclear Radiation: charged particles and energy that are emitted from the nuclei of radioisotopes Common nuclear radiation types alpha particle beta particle gamma rays
  • Slide 6
  • Alpha Decay Alpha Particle ( ): a positively charged particle made up of 2 protons and 2 neutrons (the SAME as a HELIUM NUCLEUS) Common symbol =
  • Slide 7
  • Example of alpha decay of uranium 238
  • Slide 8
  • Dangers of Nuclear Radiation Least penetrating type of nuclear radiation, can be stopped by sheet of paper or clothing
  • Slide 9
  • Beta Decay Beta Particle ( ): an electron emitted by an unstable nucleus Written as: Assigned atomic # of -1 mass of 0 (zero) How can a nucleus (which is positive), emit a negatively charged particle?
  • Slide 10
  • During beta decay, a neutron decomposes into a proton and an e-
  • Slide 11
  • Proton stays trapped in the nucleus, e- released
  • Slide 12
  • Example of beta decay of thorium 234
  • Slide 13
  • Product isotope has 1 proton more and 1 neutron fewer than the reactant isotope Mass number of the isotopes are equal because the emitted beta particle has essentially NO MASS
  • Slide 14
  • Beta particles pass through paper, but stopped by thin sheet of metal
  • Slide 15
  • Gamma Decay Gamma Ray ( ): a penetrating ray of energy emitted by an unstable nucleus
  • Slide 16
  • Gamma Decay NO mass and NO charge During Gamma Decay: Atomic number and mass number of the atom remains the same Energy of nucleus decreases
  • Slide 17
  • Gamma decay often accompanied by alpha or beta decay Example of thorium 234 emitting both beta particles and gamma rays as it decays:
  • Slide 18
  • Gamma rays much more penetrating takes several centimeters of lead or several meters of concrete to stop gamma radiation
  • Slide 19
  • Slide 20
  • Effects of Nuclear Radiation Background Radiation: nuclear radiation that occurs naturally in the environment
  • Slide 21
  • When nuclear radiation exceeds background levels, it can damage the cells and tissues of your body
  • Slide 22
  • Slide 23
  • Effects of Nuclear Radiation Nuclear radiation can ionize atoms (when cells are exposed to nuclear radiation, the bonds holding together proteins and DNA molecules may break cells may no longer function properly)
  • Slide 24
  • Effects of Nuclear Radiation , , and are all forms of ionizing radiation The extent of the damage of external nuclear radiation is dependent on the penetrating power of the radiation
  • Slide 25
  • Beta particles cause more damage than alpha particles, but less than gamma rays Gamma rays can penetrate deeply into the human body, potentially exposing all organs to ionization damage
  • Slide 26
  • Detecting Nuclear Radiation Although you cant see, hear, or feel the radioactivity around you, scientific instruments can measure nuclear radiation Geiger Counters Film Badges
  • Slide 27
  • 10.2 Rates of Nuclear Decay
  • Slide 28
  • Nuclear Decay By studying the radioactive nuclei of an object we can determine how old the object is. Because most materials contain at least trace amounts of radioisotopes, scientists can estimate how old they are based on rates of nuclear decay.
  • Slide 29
  • Slide 30
  • Half-Life Half-life: the time required for one half of a sample of a radioisotope to decay After one half-life, half of the atoms in a radioactive sample have decayed, while the other half remain unchanged After two half-lives, half of the remaining have decays, leaving one quarter of the original sample unchanged
  • Slide 31
  • Half-Life Example Iodine Half-life= 8.07 days After one half-life (8.07 days) half of the original sample remains After 2 half-lives (16.14 days) one quarter of the original remains After 3 half-lives (24.21 days) one half of one quarter remains, or 1/8 (one eighth) and so on
  • Slide 32
  • Half-Lives Vary Half-lives can vary from fractions of a second to billions of years Unlike chemical reaction rates, which vary with the conditions of a reaction, nuclear decay rates are constant!!!
  • Slide 33
  • Radioactive Dating Method used for determining the age of objects using the half-lives of Carbon 14 Radiocarbon dating: determining the age of an object by comparing its carbon-14 levels with carbon-14 levels in the atmosphere.
  • Slide 34
  • Radioactive Dating Carbon-14 has a half-life of 5,730 years. Carbon-14 is formed in the upper atmosphere when neutrons produced by cosmic rays collide with nitrogen-14 atoms. The radioactive carbon-14 undergoes beta decay to form nitrogen-14.
  • Slide 35
  • Slide 36
  • Slide 37
  • Using Carbon-14 to Date Living organisms absorb the carbon (CO 2 ) from the atmosphere, but when they die they stop absorbing it and the levels do not change. From this point levels start to decrease as the radioactive carbon decays. The levels in the object are then compared with levels in the atmosphere.
  • Slide 38
  • Example: if an object has half the amount of carbon-14 in it as in the atmosphere, then we know the object is about 5, 730 years old (which is one half-life for carbon-14)
  • Slide 39
  • Slide 40
  • Carbon-14 Dating Carbon-14 or radiocarbon dating can be used to date any carbon-containing object less than 50,000 years old. After this point, there is too little carbon-14 left to be measurable Objects older than this use radioisotopes with longer half-lives The older the object the lower the levels of radioisotopes present
  • Slide 41
  • Slide 42
  • 10.3 Artificial Transmutation
  • Slide 43
  • Transmutation Transmutation: the conversion of atoms of one element to atoms of another. It involves a nuclear change, not a chemical change. Transmutations can either occur naturally (nuclear decay) or artificially. Scientists can perform artificial transmutations by bombarding atomic nuclei with high-energy particles such as protons, neutrons, or alpha particles.
  • Slide 44
  • Transuranium Elements Transuranium Elements: Elements with atomic numbers greater than 92 (uranium) All transuranium elements are radioactive and generally not found in nature Scientists can create a transuranium element by the artificial transmutation of a lighter element Useful transuranium elements Americium-241: used in smoke detectors Plutonium-238: energy source for space probes
  • Slide 45
  • Slide 46
  • Particle Accelerators Sometimes transmutations will not occur unless the bombarding particles are moving at extremely high speeds. To achieve these high speeds scientists use particle accelerators.
  • Slide 47
  • Particle Accelerator These accelerators move charged particles at speeds very close to the speed of light The particles are then guided toward a target, where they collide with atomic nuclei and transmutations are allowed to occur These collisions have also lead to the discovery of more subatomic particles Quarks: protons and neutrons are made up of these even smaller particles
  • Slide 48
  • Large Hadron Collider (LHC)
  • Slide 49
  • 10.4 Fission & Fusion
  • Slide 50
  • Question What holds the nucleus together? Its full of positive particles, so why dont they push each other away? What keeps the protons and neutrons together? Clearly, there must be an attractive force that binds the particles
  • Slide 51
  • Answer Strong Nuclear Force: the attractive force that binds protons and neutrons together in the nucleus Over very short distances, the strong nuclear force is much greater than the electric forces among protons
  • Slide 52
  • Forces in the Atom
  • Slide 53
  • Electric Force Question: What determines the strength of the electric force? Answer: The number of protons
  • Slide 54
  • Electric Force The greater the number of protons, the greater is the electric force that repels the protons Larger nuclei have a stronger repulsive force than a smaller nuclei As a result, the nucleus will become unstable (or radioactive) when the strong nuclear forces cant overcome the repulsive electric forces among protons.
  • Slide 55
  • Nucleus Size & Radioactivity Because of the size issue, there is a point beyond which all elements are radioactive. Once they become large enough, th

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