Summer Research Program for Science Teachers

Peter Torpie

New Milford HS, New Jersey



Finding the Average Atomic Mass of the Element Chocolatium


In this exercise you will find the Average Atomic Mass of a new element called Chocolatium (the symbol is MM). You will be given a large sample of Chocolatium containing several different isotopes of the element.  You will have to find the natural abundance of each of the different isotopes, and using this and the atomic mass of each isotope (see table below), you will find the Average Atomic Mass of Chocolatium that will be entered onto the Periodic Table of Candy.


Isotope                                            Atomic Mass

Brown                                                 10.5

Green                                                  11.2

Yellow                                                10.0

Orange                                               11.7

Blue                                                    11.4


The Red isotope will be returned to the teacher because it is so dangerous and is his favorite color anyway.

The natural abundance of an element is a measure of how common that element is.  It is found by counting how many of that there is and dividing that number by the total number of isotopes in your sample.  For example:

# Brown M&M’s/number of M&M’s of all colors in your sample = natural abundance

You will then use this information in the average atomic mass formula.


Isotope                                    number found             total number                natural abundance

Brown                                                              /                                  =

Green                                                              /                                  =

Yellow                                                            /                                  =

Orange                                                          /                                   =

Blue                                                             /                                    =


You can use the natural abundance and the element’s atomic mass to find the average atomic mass of Chocolatium that will be entered on the Periodic Table of Candy by using this formula:

Average Atomic Mass = (Mass of first isotope X Natural Abundance of first isotope) + (Mass of second isotope X Natural Abundance of second isotope) + ….


Average Atomic Mass = (_____ X _____) + (_____ X _____) + (_____ X _____) +

                                       (____ X _____) + (_____X_____)


Average Atomic Mass = (________) + (________) + (________) + (________) +  


Average Atomic Mass = ________


New Jersey State Core Curriculum Standards

5.1, 5.2, 5.3, 5.4, 5.7


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