MHS Chemistry
Electrons & Probability

In this activity you will model the behavior of an electron with pennies.  Electrons do not occupy orbits around a nucleus. They do occupy orbitals, which are regions in spaceof high probability (>90%) of finding a given electron.  An electron can be anywhere inside an orbital, sort of like a bee in it's hive's territory.  These three-dimensional locations can be difficult to draw, so we will stick with the simplest situation.

The simplest atom is the hydrogen atom, with one proton attracting one electron, and no other charged particles around to complicate things.  The atom knows no up or down or left or right, so any direction is the same to it's lone electron.  Therefore, we can plot likelihood of finding an electron vs. radius, and get a picture of the orbital.


  1. Use a piece of chalk, a meter stick, and a length of string to draw a target on the floor.  The "bull's-eye" should have a radius of 1 inch, and each successive circle should have a 2 inch larger radius.  The largest should be 15 inches.  As an alternative, you may wish to draw your target on newsprint or other large paper, and tape it to the floor.
  2. Stand 6 feet from the outside circle.  Pitch pennies (one at a time) towards the bulls-eye.  Collect any pennies that do not stay in the target, and pitch them again.
  3. When you have completed your throws, count the number of pennies in each ring.  If a penny touches a line, count it for the inner ring.  Record your data, and let your partner take a turn.
  4. Alternative: Make a smaller target on the back of a book cover, and toss beans from three feet away.
  1. Make a bar graph of your results.
  2. How many pennies did you toss?  What is 90% of this number?
  3. Which ring is the "90% Probability Boundary?"  Explain your answer.
  4. How is this a good model for a hydrogen atom?
  5. How is this not a good model for a hydrogen atom?

[Electrons & Probability score sheet][Chapter 4 Notes][MHS Chem page]