NUCLEAR CHEMISTRYOBJECTIVE: 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-unexpec
ted-steve-weatherall• Review questions:• http://ed.ted.com/lessons/radioactivity-expect-the-unexpec
ted-steve-weatherall#review• Dig deeper: • http://ed.ted.com/lessons/radioactivity-expect-the-unexpec
ted-steve-weatherall#digdeeper
Review: Radioactive IsotopesA 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 isotopeType Symbol Charge Mass Rad.Strength
Next slide
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 reactionsTotal number of atomic numbers and the total mass
numbers must be equal on both sides of the equation. Examples:
Nuclear Equations
1. 23892U 234
90Th + ?
2. 146C 0
-1e + ?3. 239
94Pu + 42He 242
96Cm + ?
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 radioisotopeNumber of Half-Lives
Elapsed time Amount remaining
0 0 100 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 Life800 Billion Bismuth-210 Atoms
Time (years)
Half Life: • http://phet.colorado.edu/en/simulation/radioactive-dating-g
ame
Number of years
Num
ber o
f rad
ioac
tive
isot
opes
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 life100g
• 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 ELEMENTReading 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)?
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