1. Unit 11 - Nuclear Chemistry
-What is the difference between fission and fusion?
-What does half-life measure?
-What are the different ways that a nucleus decays?
Considering all of the possible uses of nuclear technology, can we safely utilize this source of energy? Why/why not?

2. Nuclear radioactivity
Natural radioactivity
______________________ - emission of particles or energy from an unstable nucleus
Discovered by Henri Bequerel
Three types of radioactive decay
____________ decay (He-nucleus)
____________ decay (high energy electron)
____________ decay (high energy electromagnetic waves)

3. The nature of the nucleus
________________________
Binds protons and neutrons
Very short ranged, less than m
Overcomes proton-proton Coulomb repulsion
Band of stability

4. Generalizations - nuclear stability
Atomic number > 83: unstable
Nucleon number = 2, 8, 20, 28, 50, 82 or 126: added stability
Pairs of protons and pairs of neutrons: added stability
Odd number of both protons and neutrons less stable
Neutron: proton ratios for added stability
1:1 in isotopes with up to 20 protons
1+increasing:1 with increasingly heavy isotopes

5. Nuclear equations ____________________= number of protons in nucleus
_______________: same atomic number; different number of neutrons
___________________= number of nucleons (protons and neutrons) in nucleus
______________________
Represented by balanced equations
Charge conserved
Atomic number conserved

7. Types of radioactive decay
Alpha emission
Expulsion of helium nucleus
Least penetrating: stopped by ______________
Beta emission
Expulsion of an electron
More penetrating: 1 cm of _______________
Gamma decay
Emission of a high energy photon
Most penetrating: 5 cm of _____________

8. Radioactive decay series
One radioactive nucleus decays to a 2nd, which decays to a 3rd, which…
Three naturally occurring series
Thorium-232 to lead-208
Uranium-235 to lead-207
Uranium-238 to lead-206
Process results in a stable nucleus

9. Writing Nuclear Equations
Determine what type of decay occurs
Write what you start with on the left side of the arrow
Write the decay particle emitted on the far right
Using conservation of mass and atomic #, determine what the new nucleus will be

10. Things to remember: Alpha decay gives off a ____________________
Remaining nucleus has a mass 4 lower and atomic # 2 lower than original
Beta decay gives off a _________________
Remaining nucleus has the same mass and an atomic # 1 higher than original

11. Practice Thorium-232 undergoes Alpha decay
Radium 228 undergoes Beta decay

12. Radioactive Decay Rates
It is impossible to predict the exact moment a nucleus will decay
We CAN predict the time for ________________________________________to decay

13. Half-life Time required for 1/2 of a radioactive sample to decay
Example: 1 kg of an unstable isotope with a one-day half- life
After 1 day: 500 g remain
After 2 days: 250 g remain
After 3 days: 125 g remain
U-238 decay series: wide half- life variation

14. Calculating Half Lives
Radium-226 has a half life of 1599 years. How long would it take seven- eighths of a radium-226 sample to decay?
Step 1- List the given and unknown values
Step 2- Calculate the fraction of radioactive sample remaining
Step 3- Calculate the number of half lives
Step 4- Calculate the total time required for the radioactive decay

15. Nuclear energy There is an overall loss of mass in nuclear reactions
Why?
______________________ of mass and energy
Change in mass is related to a change in energy
______________________
Difference between masses of reactants and products

16. Nuclear Energy _________________ energy Energy out?
Energy required to break a nucleus into individual protons and neutrons
Energy out?
E=mc2
E= energy in J
M= mass defect in kg
C= speed of light
3.0e8

17. Nuclear fission Heavy nuclei splitting into lighter ones
___________________
Possible when one reaction can lead to others
One neutron in, two or more out
____________________
Sufficient mass and concentration to produce a chain reaction

18. Nuclear power plants Rely on controlled fission chain reactions
Steel vessel contains fuel rods and control rods
Full plant very intricate
Containment and auxiliary buildings necessary
Spent fuel rods
Contain fissionable materials U-235, Pu-239
Disposal issues not settled

20. Many possible fission fragments

21. Nuclear fusion Less massive nuclei forming more massive nuclei
Energy source for Sun and other stars
Requirements for fusion
___________________________
__________________________
Sufficient confinement __________

22. Source of nuclear energy
Ultimately connected to origins of the Universe and the life cycles of stars
Big Bang theory
Incredibly hot, dense primordial plasma cools, creating protons and neutrons
Continued cooling leads to hydrogen atoms which collapse gravitationally into 1st generation stars
Stellar evolution
Interior temperatures and densities suitable for fusion of heavy elements beyond hydrogen and helium
Certain massive stars explode in supernovae, spreading heavy elements (some radioactive)
Ultimate source: gravitational attraction!