This document discusses radioactive decay and half-life calculations. It defines key terms like radioactivity, radiation, and half-life. It then provides examples of calculations to determine the amount of radioactive material remaining after a given number of half-lives. Specifically, it includes 8 examples of half-life calculations and shows the step-by-step work and answers. The calculations demonstrate how to use the half-life formula to find the amount of material remaining over time.

1. 1
Radioactivity Review and
Half-Life
Chemistry I

2. Band of Stability

3. 3

4. Radioactive Decay Series

5. 5

6. 6
Radioactivity
• An unstable atomic nucleus
emits a form of radiation
(alpha, beta, or gamma) to
become stable.
• In other words, the nucleus
decays into a different atom.

7. 7
Radiation
• Alpha Particle – Helium nucleus
• Beta Particle – electron
• Gamma Ray – high-energy
photon

8. 8
Electromagnetic Spectrum

9. 9
Half-Life
• Amount of time it takes for
one half of a sample of
radioactive atoms to decay.

10. 10

11. 11

12. 12
Half-Life Calculation #1
• You have 400 mg of a
radioisotope with a half-life of
5 minutes. How much will be
left after 30 minutes?

13. 13
Half-Life Calculation #2
• Suppose you have a 100 mg
sample of Au-191, which has
a half-life of 3.4 hours. How
much will remain after 10.2
hours?

14. 14
Half-Life Calculation #3
• A radioisotope has a half-life
of 1 hour. If you began with
a 100 g sample of the
element at noon, how much
remains at 3 PM? At 6 PM?
At 10 PM?

15. 15
Half-Life Calculation # 4
• How many half-lives have
passed if 255 g of Co-60
remain from a sample of
8160 g?

16. 16
Half-Life Calculation # 5
• Suppose you have a sample
containing 400 nuclei of a
radioisotope. If only 25
nuclei remain after one hour,
what is the half-life of the
isotope?

17. • 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 0.625 grams of
this strontium-90 remain?
17
Half-Life Calculation #6

18. • Sodium-25 was to be used in an
experiment, but it took 3.0 minutes to
get the sodium from the reactor to the
laboratory. If 5.0 mg of sodium-25 was
removed from the reactor, how many
mg of sodium-25 were placed in the
reaction vessel 3.0 minutes later if the
half-life of sodium-25 is 60 seconds?
18
Half-Life Calculation #7

19. Half-Life Calculation #8
• Three grams of Bismuth-218 decay to
0.375 grams in one hour. What is the
half-life of this isotope?
19

20. 20
Answers to Half-Life
Calculations
• Half-Life Calculation #1
– 6.25 mg
• Half-Life Calculation #2
– 12.5 mg
• Half-Life Calculation #3
– 12.5 g, 1.5625 g, 0.09765625
g

21. 21
Answers to Half-Life
Calculations
• Half-Life Calculation #4
– 5 half-lives
• Half-Life Calculation #5
– 15 minutes
• Half-Life Calculation #6
– 2016

22. Answers to Half-Life Calculations
• Half-Life Calculation #7
– 0.625 mg
• Half-Life Calculation #8
– 20 min.
22