NAME ____________________________________________________
DATE _____________
LEARNING OBJECTIVE – Today you will calculate the average atomic mass of an isotope in order
to construct a comprehensive report of experimental data related to relative abundance.
DO NOW – Use the information in the table to determine the average atomic mass of oxygen.
Oxygen
Isotope
X
Y
Z
Number of
Protons
8
8
8
Number of
Neutrons
10
8
9
Abundance
Percentage
0.2%
99.76%
0.04%
AVERAGE ATOMIC MASS OF BEANIUM
This lab exercise is designed to show you isotopes of an element in a simulation form. You will be asked to gather data
about the “isotopes” and organize the data. If atoms were as large as beans they could be sorted, counted, and massed. In
this experiment you will sort, count, and mass four different kinds of beans and imagine that you are observing four
different isotopes of the same element (let’s call it BEANIUM). The four different isotopes are black, brown, red and white
in color. You will determine the percent abundance of each isotope and calculate the average atomic mass of beanium.
Introduction
Write a brief background of isotopes and average atomic mass in the space provided below. Be sure to include
information about how isotopes differ. You should discuss (a) isotopes, and how they differ; (b) why the average atomic
mass of an element as reported on the periodic table is different from the mass number, and (c) the relationship
between the percent abundance of an isotope of an element to the average atomic mass of the element.
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Procedure
1. Sort the isotope atoms (beans) into a group for each isotope: black, brown, red and white. Record the total number
of each type of isotope (blackium, brownium, redium and whitium) in the data table.
2. Find the percent abundance for each isotope by dividing the number of individual isotope by the total number of
isotope atoms (black, brown, red, white) and multiplying by 100%. Record on the data table.
3. Determine the mass of the isotope:
a) Using a balance, find the total mass of each of the four isotope groups and record on data table
b) find the typical mass of one atom of each isotope by dividing the total mass of each isotope by the
number of that isotope. Record on the data table.
4. Determine the atomic mass for BEANIUM based on the percent abundance and the mass of each isotope.
AVERAGE ATOMIC MASS =
PERCENT ABUNDANCE OF ISOTOPE x MASS OF ISOTOPE
5. Add the products in the last column to find the average atomic mass of the element Beanium.
6. Place all the beans back in the plastic bag.
Data
Total number of Beanium isotope atoms in the bag = ____________
NAME OF ISOTOPE
NUMBER OF
INDIVIDUAL
ISOTOPES
PERCENT
ABUNDANCE OF
ISOTOPE
TOTAL MASS
(GRAMS)
MASS OF
ISOTOPE
(GRAMS)
AVERAGE
ATOMIC MASS
OF ISOTOPE
AVERAGE ATOMIC MASS OF BEANIUM
Graph (Create a graph to compare the percent abundance of each of the four isotopes. Include a legend.)
Check for Understanding

Calculate the average atomic mass of the element described below (both atoms of the same element).
Then use the periodic table to identify the element.