1. REVIEW What are the four forces in the atom? Explain them? Gravity - the weakest Electromagnetic - Attraction between + and - Strong - Keeps the atom together Weak Responsible for radioactivity

2. Radioactivity Lab What is radioactivity? When do we use radioactivity? What is a half life?

3. Radioactivity ► Radioactivity occurs when nucleus of atom emits particles to become stable Eventually the strong force can not hold the atom together, a particle is emitted. The atom is now radioactive

4. Definitions ► A half life is the time it takes for half of a sample to decay ► Decay- turn from an unstable radioactive isotope to a stable atom

5. Understanding our lab ► Think of our disk as a penny. As you flip a coin you have a 50% chance of flipping tails.

6. Understanding Process ► Baggie represented the sample ► Each shake represented a half-life ► About 50% of radioactive sample became stable with each shake

7. Half-Life ► Half life of each radioactive element is different ► U-238 takes 4.9 x 10 9 years ► C-14 takes 5700 years In nuclear reactors In bones

8. Half-Life ► If it took 7 shakes (half- lives) for entire sample to decay and the sample was carbon (1 half life = 5700yrs) ► 7 x 5700 = 39,000 yrs.

9. Half-Life Problems ► If a sample material has a half life of 20 years and goes through 3 half lives how much parent atom and daughter atom remain? 100 g How much did we start with? If the whole sample is radioactive that means nothing is stable 0 Now the sample will go through 1 half life, where half of it will decay to become stable Half of 100 50 If 50g is now radioactive the rest of the original 100g now must be stable 50 + = 100 Now only 50g is radioactive, what is half of 50? 25 If 25g is radioactive the rest of the original 100g is now stable 75 Now what is half of 25g? 12.5 Our original minus the 12.5g 87.5 Parent Daughter

10. Half-life Problems ► If the sample was uranium 238 and each half-life was 4.9 x 10 9 years, how many years have gone by? ► 4.9 x 10 9 years x 3 = 14.7 x 10 9 years Time of half life# of half lives

11. A dinosaur bone was found in Slinger, WI yesterday (ok, I lied). Pretend this bone was tested and the scientist found that the bone has 3.125g of radioactive Carbon 16. How long ago did this dinosaur live? A half life of Carbon 16 is 5.2 million years. Parent Daughter

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