1. Nuclear Chemistry
Nuclear Chemistry

2. Facts About the Nucleus
Very small volume compared to volume of atom
Essentially entire mass of atom
Very dense
Composed of protons and neutrons that are tightly held together
called Nucleons 2

3. Facts About the Nucleus (cont.)
The number of neutrons is calculated by subtracting the atomic number from the mass number.
The nucleus of an isotope is called a nuclide.
Less than 10% of the known nuclides are nonradioactive. Most are radionuclides. 3

4. Electromagnetic Spectrum

5. Radioactivity Henri Becquerel (1896)
Accidentally placed a uranium sample on some unexposed photographic film, which caused it to be “developed”
Uranium – one of the naturally radioactive elements

6. During radioactive decay, atoms of one element are changed into atoms of a different element.
In order for one element to change into another, the number of protons in the nucleus must change
All nuclides with 84 or more protons are radioactive
We describe nuclear changes using nuclear equations.
Atomic numbers and mass numbers are conserved

7. Marie Curie
One of the first female scientist allowed to work in a lab, but only b/c she worked with her husband Pierre (who was later killed by a horse & buggy).
She was then granted permission from the University to continue to work by her self.
Discovered 2 elements: Radium & Polonium (she named it for her motherland Poland).
Only person to win a Nobel Prizes in 2 different categories; Physics (1903) and Chemistry (1911)
Kept radioactive materials in her pocket
Died of leukemia from radioactive materials
Her work & body are at a museum dedicated to her in Poland. Which are kept under lead because they are still radioactive today!
Total time of video 2: 56

8.  Alpha Decay  An  particle contains 2 protons and 2 neutrons.
= Helium nucleus
Loss of an alpha particle means
Atomic number decreases by 2
Mass number decreases by 4 5

9.  Beta Decay  A  particle is like an high-speed electron
Moving much faster
Found in the nucleus
When an atom loses a  particle its:
Atomic number increases by 1
Mass number remains the same
In beta decay a neutron changes into a proton:

10.  Gamma Emission  Gamma () rays are high energy photons
Gamma emission occurs when the nucleus rearranges
No loss of particles from the nucleus
No change in the composition of the nucleus (same atomic number and mass number)
Generally occurs whenever the nucleus undergoes some other type of decay 6

11. Penetrating Power

12. Radioisotopes radioactive isotope half – life
many elements have at least 1 radioactive isotope
half – life
the time it takes for ½ of a sample of an isotope to decay

13. The longer the half-life the more slowly the rate of decay
The longer the half-life the more slowly the rate of decay. The slower the decay the less ,  and  radiation is emitted.

15. Uses for half-life? Determine the age of substance
Determine how much of a substance will be left
Ex: Carbon-dating
Half–life of carbon – 14 is 5730 years

16. Half - Life Ex: half-life of rubidium–87 is
6 X years (60 billion)
It takes 60 billion years for half of the sample to decay.
If I started out with 100 g how many grams would be left after 60 billion years?
Rb–87  Sr–87
What type of decay?

17. Half-life Problems
To solve you are going to need to know some information such as:
Half-life Time
Initial Mass
Final Mass
Number of half-lives
Total Time
If you are given some of these you can solve for the others

18. Example 1 Or you can do it the “mathy way”
Half-life of an isotope of plutonium is 140 days
The original sample contained 10.0 grams
How much is left after 420 days?
Step 1- find the number of ½ lives = (total time/ ½ life time)
Step 2- find the final mass “loopy way”
Or you can do it the “mathy way”
Final mass = (initial mass divide by 2 #halflives)

19. Example 2
Three grams of Bismuth-218 decay to grams in one hour. What is the half-life of this isotope?

20. Example 3 Half life of cesium – 137 is 30.2 years
Initial mass is 1.00 kg
How much will remain after 151 years?

21. Example 4
A 2.5 gram sample of an isotope of strontium-90 was formed in a 1960 explosion of an atomic bomb at Johnson Island in the Pacific Test Site. The half-life of strontium-90 is 28 years. In what year will only grams of this strontium-90 remain?

22. Example 5
The half-life of carbon-14 is 5730 years. How old is a fossil that once contained 100. g of C-14 and it now contains g?

23. Beneficial Uses of Radioisotopes
Food Preservation-
kills microorganisms – molds and bacteria
Radiotracers-
radioactive labels – used to follow a specific substance through a natural system
Iodine – 131, used to see Thyroid Issues
Barium sulfate, used to detect Gastrointestinal problems

24. Cancer treatment cancer cells are more sensitive to radiation
Teletherapy – narrow beam of high – intensity gamma radiation used to destroy tumors
Radioactive “seeds” – implanted in tumors – emit beta and gamma radiation and kill surrounding cancer cells
Chemotherapy is not radiation since it uses chemicals to destroy cancer cells