This resource is part of the Atoms and the Periodic Table Bundle!
This Eggium Isotope and Atomic Mass activity is great for helping your students to understand what isotopes are, how mass number and atomic mass are different, and why atomic mass is a decimal number on the Periodic Table. If you ask your students why atomic mass is a decimal number on the Periodic Table, you will usually get an array of answers including the most common misconceptions– that electrons add a little mass, that there are parts of protons or neutrons in the nucleus, or that chemists have very precise equipment for measuring mass and they know mass out to many decimal places. This activity drives home the real reason why -- the atomic mass is a weighted average mass of all of an element's known isotopes!
The materials for this activity are simple! Plastic Easter eggs (or Petri dishes or sandwich bags!) are your atomic nuclei...pom-poms are your subatomic particles. The fictitious element ‘Eggium’ has a bunch of isotopes, for which students will calculate natural abundance and the weighted atomic mass.
I always do this activity as a class activity so that I can talk the class through the steps and facilitate a discussion, but if you have enough time and resources, you could make the following materials for groups of 3 or 4 students.
For a whole-class activity you will need:
10 plastic Easter eggs (If you don’t have Easter eggs, simply use Petri dishes or even just sandwich bags!)
Around 100 small pom-poms in one color
Around 70 small pom-poms in another color
A black Sharpie marker
10 paper plates or trays [optional]
There are 2 practice/formative assessment worksheets included with answer keys -- one on isotopes and one on calculating weighted atomic mass using percentage natural abundances of actual elements.
All of the student pages and answer keys are also included as editable documents in the download!
Please check out my other intro to atomic structure resources:
Atoms Cornell Doodle Notes and Powerpoint
Bohr Diagrams Atom Manipulatives Activity
Thanks for looking!