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Nuclear Chemistry. Electromagnetic Radiation. All objects give off radiation Radioactive unstable nuclei (more neutrons than protons) decay to different element with different atomic number Most atoms remain unchanged Common properties of EMR form of energy and has no mass

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Nuclear Chemistry


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    Presentation Transcript
    1. Nuclear Chemistry

    2. Electromagnetic Radiation All objects give off radiation Radioactive unstable nuclei (more neutrons than protons) decay to different element with different atomic number Most atoms remain unchanged Common properties of EMR • form of energy and has no mass • travels at the speed of light (3 X 108 m/s) • can travel through a vacuum; does not need a medium like H2O • emitted by atoms as they decay or after they are energized • moves through space as packets of energy called photons • energy of photons is related to the frequency

    3. Two types of radiation Ionizing radiation x-rays, gamma rays greatest energy high frequency; short wavelength cause particles like electrons to be ejected exposure can cause great damage to tissues Non-ionizing radiation radio waves, microwaves, infrared, visible light, ultraviolet lower energy low frequency; long wavelength exposure does not cause great damage to tissues

    4. Atoms Particle location charge mass proton p+ nucleus +1 1 g/mol neutron no nucleus 0 1 g/mol electron e- outside nucleus -1 0 in energy levels

    5. Atomic number = number of protons = number of electrons if atom is neutral identifies the element Mass number = number of protons + neutrons

    6. Isotopes Atoms of the same element having different number of neutrons Radioisotope Radioactive (ionizing) Decays spontaneously Symbol mass # 90 Sr atomic # 38 Name Add mass number to the name of the element or symbol Example: strontium-90 or Sr-90

    7. Stability of isotopes stable isotopes do not decay spontaneously 1500 known isotopes and only 264 are stable 85% of all isotopes are unstable can be predicted using proton to neutron ratio nuclei > atomic number 84-alpha

    8. Radioactive decayemission of radiation is one way that an unstable nucleus is transformed into a more stable one with less energy Alpha emission  alpha particle is composed of 2 protons and 2 neutrons nucleus of helium-4 atom more massive than beta particle poor penetrating power slow speed potential to cause great damage to tissue produces new particle with lower atomic # and mass # symbols of alpha particle 42He     and     example of alpha decay 22688Ra   42He   +    22286Rn

    9. Beta emission  beta particle is an electron beta emission is equivalent to the conversion of a neutron to a proton smaller than an alpha particle moves faster and penetrates better than alpha produces new particle with higher atomic # and same mass # symbols of beta decay 0-1e      and      0-1      and        example of beta decay 146C   0-1e    +    147N

    10. Gamma  gamma is a form of electromagnetic radiation high energy photons represents energy lost when the remaining nucleons reorganize into more stable arrangements moves at speed of light not a particle penetrates best of all types of radiation no change in particle that undergoes gamma decay symbols 00     and       

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

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

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

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

    15. Nuclear Energy In order to produce energy, an atom must lose mass. Nuclear reaction releases1 million times more energy than chemical reaction Atoms before iron will undergo fusion to produce energy Atoms after iron will undergo fission to produce energy Iron is the “nuclear sink”  It will not undergo fusion or fission.

    16. Fission advantage- can do it now disadvantage-fuel hard to get and produces waste products that are radioactive chain reaction-reaction continues because an ejected particle form the original reaction can split more nuclei critical mass-minimum volume of fissional material necessary to keep a chain reaction going Nuclear power plants produce electricity  (nearly 20% of U.S. needs; 110 plants) produce heat to boil water to make steam to turn turbines Parts of power plant • fuel rods-pellets of uranium dioxide • control rods-absorb neutrons to control rate of reaction • moderator-slows down high-speed neutrons • generator-produces electricity • cooling system-cools steam

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

    18. Risks and Benefits of nuclear chemistry Benefits • Energy source • Tracer studies-isotopes used to trace systems • medicine-  find and treat diseases • petroleum pipelines • agriculture • Irradiation –sterilization • medicine • prevent spoilage

    19. Risks • 4 possible biological effects • radiation can pass through with no damage to cells • radiation can pass through with damage which the cells repair • radiation can pass through with damage that the cells cannot repair • radiation can kill the cells • Exposure • fallout from nuclear weapons testing • increased exposure to cosmic radiation during air travel • radioisotopes released into the environment from nuclear power and • and other nuclear technologies • Nuclear wastes