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### Summary

In this lab, students visualize the random nature of atomic decay (or first order chemical reactions). It helps them answer the inevitable question of what happens when a decaying material reaches a single particle of the species. It also helps them realize the important difference between macroscale and microscale phenomena.

### Grade Level

High school

### Objectives

By the end of this lesson, students will

- be more familiar with how nuclear decay occurs.
- better understand the idea of a half-life.

### Chemistry Topics

This lesson supports students’ understanding of

- half-lives

### Time

**Teacher Preparation**: 30 minutes

**Lesson**: 20–60 minutes

### Materials

For each group:

- A bag of 20 pennies

### Safety

Have students wash their hands after handling pennies.

### Teacher Notes

- If you don’t have time to make bags of 20 pennies apiece, you could have a bunch of pennies and have students count out their own sample.
- Candy with a symbol could also be substituted for pennies (M&M’s for example).

### For the Student

**Half-Life Lab**

###### Lesson

**Background**

Radioactive elements decay by several methods so their nuclei can give off energy to become more stable. The rate of this decay is called the half-life. The half-life is defined as the amount of time it takes for half of the atoms in a sample of an element to decay into another element. The half-life is not an exact measurement because it is impossible to tell exactly when each atom decays, so it’s what happens on average. This experiment will show you how decay really happens.

When you flip a penny, there is a 50% chance that it will turn up “heads,” and a 50% chance that it will turn up “tails.” If you assume a penny that lands tails side up results in nuclear decay, then one flip of all of the coins should be the equivalent of one half-life. This experiment will familiarize you with how nuclear decay really occurs, and it will help you become more familiar with half-life calculations.

**Problem**

To mimic a radioactive isotope’s half-lives by flipping a coin.

**Materials**

A bag of pennies

**Procedure**

1. Record the bag number. Count the number of pennies in the bag. You should have about 20 pennies to work with.

2. Shake and drop the pennies. Record how many pennies end up as heads. These are the atoms that did NOT decay and are still the original element. Set aside the pennies that fell tails side up because they represent the atoms that decayed into a different element.

3. Flip the remaining coins. Again, record the number of pennies that landed heads side up and set aside the tails side up pennies.

4. Repeat until you have zero pennies land on heads.

5. Repeat steps 2–4 to record a second trial of data.

**Results**

Bag #:___________ Number of pennies returned to bag:_____________

Number of times flipped | Trial 1: Atoms Remaining | Trial 2: Atoms Remaining |
---|---|---|

0 | ||

1 | ||

2 | ||

3 | ||

4 | ||

5 | ||

6 | ||

7 | ||

8 | ||

9 | ||

10 | ||

11 | ||

12 | ||

13 | ||

14 | ||

15 | ||

16 |

**Analysis**

- How many half-lives
*should*it have taken to get to one atom? - How many flips did it actually take in each of the trials?

Trial 1:

Trial 2:

- Each flip is equivalent to a half-life. Did your number of half-lives differed from what you expected? Why?