Atomic Candy
Time: 30-45 minutes
Materials (per group)
50 pieces of plain 1 re-sealable bag*
Graph paper
M&M™ candy*
*Bags will be prepared ahead of time with 50 M&M’s apiece.
Pencil
Students may NOT eat the M&M’s. They are reused by other students and have been
handled previously. All 50 M&M’s must be returned to their original bag at the end
of the activity so they are ready for the next group.
Introduction
Your body is made up of cells. Cells are made up of atoms. Does anyone know what an
atom is made up of? Atoms are made up of protons, neutrons, and electrons. The number
of protons, neutrons and electrons an atom has determines what element it is. Hydrogen,
for example, has one proton, no neutrons and one electron; the element sulfur has 16
protons, 16 neutrons and 16 electrons.
Sometimes atoms have a different number of neutrons. These atoms are called isotopes.
Many isotopes have an unstable nucleus, meaning the nucleus is too big to hold itself
together, or is not big enough to hold the protons and electrons together. When this
happens, the nucleus has to get rid of excess mass or particles. It does this through
radiation. When the atom becomes stable, it is no longer radioactive.
This nuclear decomposition is called nuclear decay. The length of time required for half of
the isotope to decay is the substance’s half-life. Each radioactive isotope has its own
particular half-life. However, when the amount of remaining isotope is plotted against
time, the resulting curve for every radioisotope has the same general shape.
Today, we will be finding half-lives of the element candium (M&M’s).
Directions
1. Instruct the students to form groups of 2 or 3. Give each group a bag of 50 atoms of
candium (M&Ms).
2. Tell one member of each team to gently shake the bag for 10 seconds.
3. Gently pour out the candy and count the number of pieces with the print side up.
These atoms have “decayed.” Record how many have decayed, then set them aside
and return the other (print side down) M&M’s to the bag and reseal it.
*Draw the following chart on the board as an example. Students will record the data
on one side of their graph paper and graph it on the other side.
Half-life Total Time # of Undecayed Atoms # of Decayed Atoms
0
1
2
3
4
5
6
7
8
4.
5.
6.
7.
8.
Have another team member shake the sealed bag for 10 seconds.
Repeat the process
Continue shaking, counting, and consuming until all the atoms have decayed.
Graph the number of undecayed atoms vs. time.
Repeat the experiment using half-lives of 5 seconds, 20 seconds, and 1 minute.
Compare the resulting graphs.
Discussion
Q: What is a half-life?
A: Half-life is the length of time required for one half of an isotope to decay.
Q: In the experiment, what was the half-life of the element candium?
A: The half-life of candium in this activity was 10 seconds.
Q: At the end of two half-lives, what fraction of the atoms had not decayed?
A: At the end of two half-lives, 1/4 of the original sample remained and 3/4 of the
sample had decayed into a new element.
Q: Describe the shape of the curve drawn in step 7.
A: The graph is a decreasing logarithmic curve.
Q: Is there any difference between the graphs for the different times?
A: The graphs should be very similarly shaped.