NUCLEAR CHEMISTRY
OBJECTIVE: TO EXPLAIN THE PROCESS OF
RADIOACTIVE DECAY USING NUCLEAR EQUATIONS
AND HALF LIFE
Essential Question: How do unstable
(radioactive) isotopes become stable?
Radioactivity introduction • Radioactivity video – 4 minutes
• http://ed.ted.com/lessons/radioactivity-expect-the•
•
•
•
unexpected-steve-weatherall
Review questions:
http://ed.ted.com/lessons/radioactivity-expect-theunexpected-steve-weatherall#review
Dig deeper:
http://ed.ted.com/lessons/radioactivity-expect-theunexpected-steve-weatherall#digdeeper
Review: Radioactive Isotopes
A radioactive isotope has an unstable nucleus that
undergoes spontaneous changes.
- Emits particles
- 1.
- 2.
- Emits energy in the form of __________ waves.
- Transmutates into another element
Types of Radiation
Alpha Decay
Beta decay
Gamma Decay
Particles emitted from a
radioactive isotope
Type
Symbol
Next slide
Charge Mass Rad.Strength
Radiation Strength: Explain in your notes how
each of the radioactive emissions are blocked.
Which is the most damaging (strongest)?
Strong Nuclear Force:
Holds the nucleus together
Limit to the # neutrons: A nucleus with too
many neutrons will be unstable and change
Balancing Nuclear Reactions
• Keep track of atomic number (Z) and mass number (A):
protons & neutrons
• Totals of A & Z must be the same before and after the
reaction.
• Shown by “Before”
“ After”
Nuclear reactions
Total number of atomic numbers and the total mass
numbers must be equal on both sides of the equation.
Examples:
Nuclear Equations
1.
2.
3.
238 U  234 Th + ?
92
90
14 C  0 e + ?
6
-1
239 Pu + 4 He  242 Cm
94
2
96
+?
Nuclear Equations Practice Website
Nuclear Reactions
Emission of Alpha or Beta particles
• http://phet.colorado.edu/en/simulation/beta-decay
• http://phet.colorado.edu/en/simulation/alpha-decay
Radioactive decay
No two radioactive isotopes decay at the same rate.
Therefore, decay rate can be used to identify the isotope.
Decay is measured by half life.
Half-life
• Measure of Radioactive decay rate.
• Measured as the time it takes for ½ of a sample of
radioisotope’s nuclei to decay into its products.
Half Life
Decay of a radioisotope
Number of
Elapsed time
Half-Lives
0
0
Amount
remaining
100 g
1
1.5 year
50 g
2
3 years
25 g
3
4.5 years
12.5 g
• Examples of the Half Life of Radioactive Elements
Tearing Through a Half Life
800 Billion Bismuth-210 Atoms
Time (years)
Half Life:
• http://phet.colorado.edu/en/simulation/radioactive-dating-
Number of radioactive isotopes
game
Number of years
Fission and Fusion
• http://phet.colorado.edu/en/simulation/nuclear-fission
Half life Calculations
• How much of a 100g sample of an unstable isotope
remains after 25 years if the half life is 5 years?
• Determine how many “half life intervals”.
• Calculate the amount of original sample remaining after
each ½ life
100g
• Simplify the calculations
Half Life Problems
• How much of a 100g sample of an unstable isotope
remains after 25 years if the half life is 5 years?
3.1 g
Half Life Problems
• How much of a 60g sample of an unstable isotope
remains after 2 days if the half life is 12 hours?
7.5 g
Half Life Problems
• How much of a 20 g sample of an unstable isotope
remains after 3 sec if the half life is 0.5 seconds?
Fission and Fusion
• http://phet.colorado.edu/en/simulation/nuclear-fission
ORIGINS OF ELEMENT
Reading Analysis:
Teachers' Domain: The Origin of the
Elements
Teachers' Domain: The Elements: Forged
in Stars
Got Calcium
• Where are most elements created?
• When was H and He created?
• What elements are made by small stars?
• What additional elements are made by large stars?
• What elements are made by supernovae (large exploding
stars)?