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BAG O’ ISOTOPES
Introduction:
Scientists have recently discovered the element legumium. Your assignment is to calculate the
average atomic mass of legumium based on the samples provided. The atomic number of
legumium is 2. The smallest of the isotopes, legumium-3, has an atomic mass of 3 atomic mass
units (amu). Legumium-4 has an atomic mass of 4 amu and Legumium-5 has a mass of 5 amu. The
largest isotope, legumium-6, has an atomic mass of 6 amu.
Purpose:
To calculate the average atomic mass of the newly discovered element, legumium.
Materials:
1 Bag o’ Isotopes
Procedure:
1. Copy the following chart into your notebook:
Isotope
Quantity
Mass (amu)
Total Mass (amu)
2. Record under “Isotope” on your chart each isotope as given in the introduction.
3. Count the number of each type of legumium isotope in your sample. Record this number in the
table under the “Quantity”.
4. Record the masses (provided in the introduction) of each legumium isotope in the table.
5. Calculate the Total mass for each legumium isotope (Quantity x Mass (amu) = Total Mass
(amu).
6. Calculate the average atomic mass of legumium using the following equation.
Ave. Atomic Mass = (Total Mass Isotope #1) + (Total Mass Isotope #2) + (Total Mass Isotope # 3) + (Total Mass Isotope # 4)
(Quantity of isotope #1+Quantity of Isotope#2+ Quantity of Isotope #3+ Quantity of Isotope #4)
7. In your notebook, graph the 4 isotopes and their masses. Have the different isotopes on the x axis
and the total mass of each isotope on the y axis. What type of graph is best to use?
Conclusion Questions (answer these in your notebook):
1. Calculate the number of neutrons in each legumium isotope.
2. According to the sample, which legumium isotope is most abundant in nature?
3. For each legumium isotope, give the proper isotope notation.
4. On a periodic table showing only whole numbers for the atomic weight, what would the atomic
weight of Legumium be?
5. If additional legumium-5 isotopes were added to the sample, how would the average
atomic mass of legumium be affected?