unit 9: radioactivity and nuclear chemistry · june 02, 2014 nuclear chemistry • other chemical...
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June 02, 2014
Unit 9: Radioactivity and Nuclear Chemistry
June 02, 2014
Nuclear Chemistry• Other chemical reactions involve valence electrons
and bond formation between different atoms.• Nuclear chemistry is about changes in an atoms
nucleus
http://www.livescience.com/37206-atom-definition.html
Review: What particles are found in the nucleus?
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too many protons
too many neutrons
Radioactive Decay• Nuclei that are radioactive are isotopes that are
unstable and spontaneously decompose> Becomes more stable by emitting particles or
pure energy
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Radioactive Decay• There are different types of radioactive decay:
> alpha decay> beta decay> gamma radiation> positron emission> electron capture
Different types of radiation carry different amount of energy and are able to penetrate different materials.
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Nuclear Equation• Equation representing radioactive decay• Atomic number (Z) and mass number (A) must be
conserved (has to be the same on both sides of the arrow).
Example:
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Alpha Decay• Alpha particle ( ) is produced
> alpha particle = helium nucleus: contains 2 protons and 2 neutrons
> Results in loss of 4 in mass number (A) and loss of 2 in atomic number (Z)
Example:
He42
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Beta Decay• Beta particle ( ) is produced
> Beta particle = high energy electron> Changes a neutron to a proton> Results in same mass number (A), increase in
atomic number by 1 (Z)
Example:
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Gamma radiation• Gamma radiation ( ) is produced
> Gamma radiation = high-energy photon> Often accompanies other types of decay
Example:
http://www.physics.isu.edu/radinf/gamma.htm
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Positron Emission• Positron ( ) is produced
> Positron = particle with the same mass as the electron but with a positive charge
> Changes a proton to a neutron> Results in same mass number (A), decrease in
atomic number by 1 (Z)
Example:
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Electron Capture• Inner orbital electron captured by nucleus
> Electron combines with a proton and becomes a neutron
> Results in same mass number (A), decrease in atomic number by 1 (Z)
Example:
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Applications of nuclear chemistry: Nuclear Medicine• PET scan (positron emission tomography)
> Uses radioactive tracer that undergoes positron emission, detects gamma rays
> Used in brain function scans, cancer detection
http://en.wikipedia.org/wiki/File:PET-image.jpg
http://en.wikipedia.org/wiki/File:PET-MIPS-anim.gif
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Example 1: Write balanced nuclear equation for the following: produces a positron.
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Example 2: Write a balanced nuclear equation for the following: produces a beta particle
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Example 3: Fill in the missing particle.
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Example 4: Fill in the missing particle.
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1.
2.
3.
4.
5.
6.
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http://facstaff.gpc.edu/~pgore/Levin9e/chaptertutorials/chapter03-04.html
Amount remaining = (initial amount) (1/2)n
n= number of half-lives that have passed
Half-Life• measures radioactive decay rates• Half-life: time required for one-half of a
radioisotope's nuclei to decay into its products
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To figure out how many half lives are in a given period...
n=T/t
T=amount of time
t=length of half-life
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Example 5: Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of Iron-59 is 44.5 days. How much of a 2.000-mg sample will remain after 133.5 days?
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Example 6: Gallium-68 has a half-life of 68.3 minutes. How much of a 10.0-mg sample is left after one half-life? Two? three?
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Example 7: The half-life of cobalt-60 is 5.272 years. How much of a 15g sample is left after 21.088 years?