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CHAPTER 22 Nuclear Chemistry

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Nuclear Stability C. Johannesson Half-life Half-life (t ) Time required for half the atoms of a radioactive nuclide to decay. Shorter half-life = less stable. – PowerPoint PPT presentation

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Title: CHAPTER 22 Nuclear Chemistry


1
CHAPTER 22Nuclear Chemistry
2
Types of Radiation
  • Isotopes - atoms of the same element with the
    same number of protons but different numbers of
    neutrons
  • Radioisotopes isotope with an unstable nucleus
    that emits radiation to become a more stable
    nucleus
  • Radioactive Decay spontaneous reaction in which
    unstable nuclei lose energy in the form of
    nuclear particles

3
Nuclear Stability
  • Why do atoms decay anyway
  • need stable ratio of neutrons to protons
  • Small atoms are stable with a 1 to 1 ratio of
    protons to neutrons
  • As the atomic number increases, atoms tend to
    have more neutrons than protons with stable ratio
    increasing to 1 to 1.5
  • The type of unbalance that is present in the
    nucleus determines the type of decay.

4
Nuclear Stability
5
Half-life
  • Half-life (t½)
  • Time required for half the atoms of a radioactive
    nuclide to decay.
  • Shorter half-life less stable.

6
Half-life
mf final mass mi initial mass n of half-lives
7
Half-life
  • Fluorine-21 has a half-life of 5.0 seconds. If
    you start with 25 g of fluorine-21, how many
    grams would remain after 60.0 s?

WORK mf mi (½)n mf (25 g)(0.5)12 mf 0.0061
g
GIVEN t½ 5.0 s mi 25 g mf ? total time
60.0 s n 60.0s 5.0s n 12
8
Types of Nuclear Particles
  • Alpha particle (a)
  • Composition 2 protons, 2 neutrons
  • Symbol 4He or a
  • Charge 2
  • Penetrating power low, stopped by paper or cloth

9
  • Beta particle (ß)
  • Composition 1 electron
  • Symbol -1 e
  • Charge -1
  • Penetrating power 100 times greater than alpha,
    stopped by wood or concrete

10
  • Gamma ray (? )
  • Composition electromagnetic waves
  • Symbol ?
  • Charge 0
  • Penetrating power 1000 times greater than beta,
    stopped by lead or 6 feet of concrete

11
Types of Nuclear Decay
  • Alpha Emission

Numbers must balance!!
12
Types of Nuclear Decay
  • Beta Emission
  • Positron Emission

13
Types of Nuclear Decay
  • Electron Capture
  • Transmutation
  • One element becomes another.

14
Fission vs. fusion
15
F ission
  • splitting a nucleus into two or more smaller
    nuclei
  • 1 g of 235U 3 tons of coal

16
F ission
  • chain reaction - self-propagating reaction
  • critical mass - mass required to sustain a
    chain reaction

17
Fusion
  • combining of two nuclei to form one nucleus of
    larger mass
  • thermonuclear reaction requires temp of
    40,000,000 K to sustain
  • 1 g of fusion fuel 20 tons of coal
  • occurs naturally in stars

18
Fission vs. Fusion
FISSION
FUSION
  • fuel is abundant
  • no danger of meltdown
  • no toxic waste
  • not yet sustainable
  • 235U is limited
  • danger of meltdown
  • toxic waste
  • thermal pollution
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