Name: _______________________________ Date: ______________________ Period: _______
Isotopes of Pastanium
Goal: To use a model “element”, pastanium, to understand how atomic mass of
an element is determined based on percent abundance of isotopes.
Materials:
1. Pastanium
2. Balance
3. Calculator
Procedure:
1. Define Isotope:
a. __________________________________________________________________
__________________________________________________________________
2. On your table is a container that holds pastanium atoms. The differences
between the istotopes of this element are very distinct. How are different
isotopes of pastanium represented in your container?
a. __________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
3. Count the total number of atoms in your container and record this number
in your data table:
4. Sort the pastanium atoms into groups, each representing a different
isotope. Count the number of each type of isotope. Record these numbers
in your data table.
5. Determine the percent abundance of each isotope in the sample:
a. For each isotope: divide the number of atoms in that isotope by the
total number of atoms in the entire sample. Record this number in
the data able as percent abundance (Do not multiply by 100, keep
them in decimal form).
6. Determine the atomic mass of each isotope in the following manner:
a. First, weigh each group of isotopes using a balance. Record these
values as “total mass of isotope” in your data table. Do this for each
isotope pile.
Name: _______________________________ Date: ______________________ Period: _______
b. Determine the “mass of one atom of isotope.” Divide the “total mass
of isotope” by the “number in sample.” Record this information in
your data table. These numbers represent the “atomic mass” of a
single atom of that isotope.
7. Now determine the “average atomic mass” for pastanium based on the
percent abundances of each isotope and their individual atomic masses:
a. For each isotope, multiply the percent abundance by the atomic
mass of a single atom of that isotope (you just calculated in 6b). Do
this for each isotope. Record your results below.
i. Isotope # 1:
ii. Isotope # 2:
iii. Isotope # 3:
b. Add up the results of 7a. This number represents the “average
atomic mass” of the pretend element pastanium. The same method
can be used to determine the average atomic mass for any element
on the periodic table!
i. Average Atomic Mass = __________________________
Name: _______________________________ Date: ______________________ Period: _______
Data:
Total # of atoms:
__________________
Number in Sample
Isotope # 1
Isotope # 2
Isotope # 3
Percent
Abundance
Total Mass of
Isotope
Mass of one atom
of the isotope
Questions:
1. What is your calculated average atomic mass for pastanium?
a. average atomic mass = _________________________
2. Compare the average atomic mass of pastanium to the mass of one atom
of each isotope. Is there one particular isotope that seems to have more of
an influence on the average atomic mass, or do the isotopes seem to
contribute equally? Explain….
a. __________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
3. Suppose you did this above experiment with the pretend element
“humanium.” Suppose also that the boys in the class are one isotope with
15 mass units and the girls in the class are another isotope with 20 mass
units. Determine the average atomic mass of the element humanium using
the same method you used in this activity.