1. Radioactive Dating

2. If an element is radioactive, how can you tell when its atoms are going to decay?
Some take seconds to decay to stable atoms, others take millions of years!
Half-life = amount of time it takes for half the nuclei in a sample of the isotope to decay
For each half-life, ½ of the substance decays.

3. Example problems
1. The half-life of I-123 is 13 hrs. How much of a 64 mg sample is left after 39 hrs?

4. Example Problems
2. Element Z has a half-life of 2 days. If 3 grams of a sample remain after 10 days, what was the mass of the original sample?

5. Example Problems
grams of Element Y decays to 20 grams in 10 days. What is the half-life of Element Y?

6. Carbon Dating C-14 is used to date the ages of plant/animal remains
C-14 has a half life of 5,730 yrs and is found in CO2
Plants use CO2 to make food, therefore having C-14. Animals eat plants so C-14 is added to their bodies.