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Nuclear Chemistry

Nuclear Chemistry. Atoms. A. atomic number = number of protons B.  mass number = number of protons + neutrons C. isotopes        1.  atoms of the same element having different number of neutrons        2.  radioisotope                   a.  radioactive

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Nuclear Chemistry

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  1. Nuclear Chemistry

  2. Atoms A. atomic number = number of protons B.  mass number = number of protons + neutrons C. isotopes        1.  atoms of the same element having different number of neutrons        2.  radioisotope                   a.  radioactive                   b.  decays spontaneously 3.  symbol                   mass #     90                                                                Sr                                         Atomic #     38 4.  name                   a.  add mass number to the name of the element                   b.  example:  strontium-90  or Sr-90        5.  stability of isotopes                    a.  stable isotopes do not decay spontaneously b.  1500 known isotopes and  only 264 are stable c.  85% of all isotopes are unstable d.  can be predicted using proton to neutron ratio                 - over atomic # 83 unstable

  3. Radioactive Decay Emission of radiation is one way that an unstable nucleus is transformed into a more stable one with less energy

  4. Radioactive Decay:Alpha Emission 1.  alpha particle is composed of 2 protons and 2 neutrons 2.  nucleus of helium-4 atom 3.  more massive than beta particle 4.  poor penetrating power 5.  slow speed 6.  potential to cause great damage to tissue 7.  produces new particle with lower atomic # and mass # 8.  symbols of alpha particle 42He     and    α 9. example of alpha decay 22688Ra   42He   +   22286Rn

  5. Radioactive Decay:Beta Emission 1.  beta particle is an electron 2.  beta emission is equivalent to the conversion of a neutron to a proton 3.  smaller than an alpha particle 4.  moves faster and penetrates better than alpha 5.  produces new particle with higher atomic # and same mass # 6.  symbols of beta decay 0-1e      and      0-1β      and       β 7.  example of beta decay 146C   0-1e   +   147N

  6. Radioactive Decay:Gamma 1.  gamma is a form of electromagnetic radiation 2.  high energy photons 3.  represents energy lost when the remaining nucleons reorganize into more stable arrangements 4.  moves at speed of light 5.  not a particle 6.  penetrates best of all types of radiation 7.  no change in particle that undergoes gamma decay 8.  symbols 00γ     and       γ

  7. Radioactive Decay:Positron Emission 1.  positron is a positive electron 2.  produces a new particle with lower atomic # and same mass # 3.  positrons have a very short life because it is annihilated when it collides with an electron, producing gamma rays 01e   +   0-1e      2 00γ 4.  example of positron  emission 3819K   3818Ar   +   0+1e

  8. Radioactive Decay: Electron Capture 1.  only type of radioactive decay in which the particle is on the reactant side of the equation (electron is consumed rather than formed) 2.  electron 3.  converts a proton to a neutron 11p   +   0-1e   10n 4.  example of electron capture 10647Ag   +   0-1e   10646Pd

  9. Artificial Radioactivity  (Bombardment reactions) A.  make a ‘new’ element by bombarding an element with a particle B.  Four particles involved      1.  target nucleus is the stable isotope that is bombarded      2.  projectile (bullet)  is the particle fired at the target nucleus      3.  product is the heavy nucleus produced in the reaction      4.  ejected particle is the light nucleus or particle emitted from the reaction      5.  example: target nucleus   +   projectile      product nucleus   +   ejected particle 2713Al             +        42He      3015P             +        10n

  10. Nuclear Energy In order to produce energy, an atom must lose mass. 1.  Nuclear reaction releases 1 million times more energy than chemical reaction 2.  Atoms before iron will undergo fusion to produce energy 3.  Atoms after iron will undergo fission to produce energy 4.  Iron is the “nuclear sink”  It will not undergo fusion or fission.

  11. Nuclear Energy: Fission 1.  Splitting of one atom into two smaller atoms 2.  advantage- can do it now 3.  disadvantage-fuel hard to get and produces waste products that are radioactive 4.  Chain reaction       a.  reaction continues because an ejected particle form the original reaction can split more nuclei       b.  critical mass-minimum volume of fissional material necessary to keep a chain reaction going 5.  Nuclear power plants       a.  produce electricity  (nearly 20% of U.S. needs; 110 plants)       b.  produce heat to boil water to make steam to turn turbines       c.  parts            1.  fuel rods-pellets of uranium dioxide            2.  control rods-absorb neutrons to control rate of reaction            3.  moderator-slows down high-speed neutrons            4.  generator-produces electricity            5.  cooling system-cools steam

  12. Nuclear Energy: Fusion 1.  involves formation of a new, more massive atom by forcing two less-massive nuclei to combine 2.  powers the sun and stars 3.  advantage-produces little waste and fuel is readily available 4.  disadvantage- can’t do it on large scale yet 5.  energy released is enormous and can be calculated using Einstein’s theory of relativity   E  =   mc2

  13. Benefits of Nuclear Chemistry 1.  Energy source 2.  Tracer studies - isotopes used to trace systems      a.  medicine - find and treat diseases b.  petroleum pipelines      c.  agriculture 3.  Irradiation - sterilization      a.  medicine      b.  food - prevent spoilage

  14. Risks of Nuclear Chemistry 1.  4 possible biological effects       a.  radiation can pass through with no damage to cells       b.  radiation can pass through with damage which the cells repair       c.  radiation can pass through with damage that the cells cannot repair       d.  radiation can kill the cells 2.  Exposure       a.  fallout from nuclear weapons testing       b.  increased exposure to cosmic radiation during air travel       c.  radioisotopes released into the environment from nuclear power and other nuclear technologies 3.  Nuclear wastes 

  15. Half-Life A.  Rate of decay of radioisotopes B.  Time required for half the atoms of a radioactive nuclide to decay C.  Pre-AP Radioactive Decay      1.  rate of decay = # of atoms that disintegrate per time      2.  A = KN           where A  =  activity  =  # disintegrations /time                      k  =  decay constant   (specific to isotope)                     N  =  number of atoms                      Nt  =   # radioactive atoms after time t                      N0  =  # radioactive atoms at time 0            Determined by                      ln Nt   =   -kt              ln = natural logarithm                           No            When t = half-life the t = t1/2     and   t1/2  =  0.693                                                                                       k              

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