1. Nuclear Chemistry

2. History of radiation
1. How are chemical reactions different from nuclear reactions?
2. What contributions did the following scientists make to nuclear radiation?
Roentgen
Becquerel
Marie and Pierre Curie
3. What makes some types of radiation more dangerous than other types?

3. Types of radiation
Alpha decay- emit an alpha particle (helium nuclei- 2 protons, 2 neutrons)
Can be represented by a nuclear equation:
Have large mass so not very penetrating (paper or skin would stop it)

4. TYPEs of radiation
2. Beta decay- neutron breaks apart into proton (which stays in nucleus) and an electron is released
More penetrating than alpha particles; stopped by aluminum foil or wood

5. TYPE OF radiation
3. Gamma radiation- high energy photon (electromagnetic radiation) emitted from nucleus
Gamma rays have no mass or charge so don’t alter atomic number/mass of atom
Very dangerous!

6. What type of radioactive decay will a radioisotope undergo?
All nuclei have a nuclear force holding the nucleus together (otherwise the protons would repel each other and fly apart)
Stability of nucleus based on proton-to-neutron ratio
Above an atomic number of 20 stable nuclei have more neutrons than protons
Nuclei with a high ratio (above the band) will undergo beta decay.
Nuclei with low ratio (below the band) will undergo positron emission or electron capture.
Nuclei with high atomic masses (above 82) tend to undergo alpha decay.

7. Positron emission and electron capture
The nucleus captures an electron from the electron cloud. The electron combines with a proton to convert into a neutron.
The mass number remains the same and the atomic number decreases since a proton was converted.
Neutron bombardment

8. Half-life
How much of a radioactive sample remains after each half-life?
-each isotope has a characteristic rate of decay
-half-life is time required for one-half of nuclei in sample to decay to products

9. Half-life What about messy numbers? ln[A]f = -(0.693/h-l)t + ln[A]i
How much U-238 will be left of a 6.00 gram sample after exactly 4 half lives?
How long will that take?
After 17,190 years, how much Carbon-14 is left of a 20.0 gram sample?
Twenty seven grams of Uranium-238 are buried in radioactive waste. How long will it take before less than
a gram remains buried?
What about messy numbers?
We use this formula to solve half-life problems with a non-integer number of half-lives.
ln[A]f = -(0.693/h-l)t + ln[A]i
[A]i = initial amount
[A]f = final amount
h-l = length of half-life
t = time elapsed

10. fission
When some nuclei are bombarded with neutrons, the nuclei split into smaller fragments
In a chain reaction, some of the emitted neutrons react with other fissionable atoms, which emit neutrons that react with other fissionable atoms

11. Fission
Releases tremendous amounts of energy (1kg of uranium produces same amount of energy as 20,000 tons of dynamite)
Nuclear reactors use controlled fission to produce useful energy

12. fission
Critical Mass is the amount of a substance that must be present in order for a chain reaction to occur.
For the atomic bomb, about 100 pounds of Uranium- 235 must be present for it to work.
If not enough mass is present, the neutrons will escape the sample without hitting other atoms, and there will be no chain reaction. This is called subcritical mass.

13. fusion Occurs when nuclei combine to produce a nucleus of greater mass
This is the main process that goes on in our sun and other stars. It is responsible for the light and energy given off – highly exothermic for small atoms.
The primary reaction is two hydrogens being built into helium.
Fusion produces lots of energy (more than fission), and its products are generally not radioactive (helium gas).
It is appealing as an energy source but fusion rxns only occur at very high temps- above 40,000,000 °C

14. Uses of radiation???