1. Ch. 25 Discovery of Electron/Nucleus and Radiation

2. Thomson’s cathode ray experiment led to the discovery of electrons.
Beam of Electrons
Positive Magnet

3. Rutherford’s Gold Foil Experiment
Rutherford’s gold foil experiment led to the discovery of the nucleus.
The positively charged alpha particles would be deflected by the positively charged nucleus.

4. Why can particles pass through atoms?
-Atoms are mostly empty space!
-If a hydrogen atom were a football field, a marble at its center would be the nucleus.

5. What happens during nuclear radiation?
-Unstable nuclei want to become stable. -They emit energy and particles to achieve stability. -Three types of radiation: alpha a, beta b, and gamma g.

6. Alpha Radiation A helium atom without the electrons, has a +2 charge.
An alpha particle is the nucleus of a helium atom.

7. Learning Check
Write the correct products after the following elements undergo alpha decay.

8. Beta Radiation
Beta Radiation= Neutron Proton, which releases an electron

9. Learning Check
Write the correct products after the following elements undergo beta decay.

10. Gamma Radiation g Often released alongside a and b radiation.
- Pure energy that is released during alpha and beta radiation. -Represented by the symbol g

12. Half-Life
Time required for one-half of the nuclei of a radioactive isotope sample to decay to products. Example: Adamantium has a half life of 1 minute. What happens if you start out with 200g?
Half Life
Time %
fraction
Mass (g)
0 min
100% 1
200
1 min
50%
1/2
100 2
2 min
25%
1/4 50 3
3 min
12.5%
1/8 25 4
4 min
6.25%
1/16
12.5

13. Learning Check
1. The half life of Carbon-14 is 5,730 years. A sample of carbon was found at an archaeological site and found to be 17,190 years old. If the original sample of Carbon-14 had a mass of 1,000g what is the current mass of the sample?
Key Information Steps
C-14 Half life = 5,730 years Find # of half lives
Current age = 17,190 years 2. Use # of half lives to find
Original mass = 1,000g current mass.
Find current mass Current mass = 125 g

14. Learning Check
2. Uranium has a half life of 4.5 billion years. If 50 g of uranium spill into the ocean, how many years will it take for the 50g to reduce to 0.78g?
Key Information Steps
Uranium’s half life = 4.5 billion years 1. Find # of half lives to
Amt. of Uranium spilled = 50 g reach 0.78g. 6 half lives
Find # of years to reduce to 0.78g 2. Multiply that # by
4.5 billion years x 6 = 27 billion years Uranium’s half life.