***PLEASE DO NOT WRITE ON THIS PAPER***
LW: THE ISOTOPES OF “PENNIUM”
PROBLEM: How many isotopes are there of the element “Pennium?”
What are the masses of each isotope and the average atomic mass of “Pennium?”
BACKGROUND: Isotopes are atoms that have the same number of protons, but different
numbers of neutrons. Thus, isotopes have nearly identical chemical properties, but some
different physical properties such as mass. The atomic mass of an element is the weighted
average of the masses of the isotopes of that element. This average is based on TWO
THINGS:
1. The mass of that isotope
2. How abundant that particular isotope is.
PROCEDURE:
1) Remove the pennies from the bag and count them to make sure that there are 20
pennies.
2) MEASURE and RECORD the total mass of ALL 20 pennies.
3) Create a data table that includes the following: PENNY, YEAR AND MASS (g).
***MAKE SURE YOU HAVE ENOUGH ROOM FOR 20 PENNIES***
4) Find the mass of each penny separately.
5) Record the mass (g) and the year that each penny was minted on the data table.
6) Place ALL 20 PENNIES back in the bag and clean up.
ANALYSIS AND CONCLUSION:
1) Inspect your data carefully. How many isotopes of “Pennium” are present? What
evidence do you have for your answer?
2) What fraction of each isotope is present (out of 20 pennies)?
3) Calculate the average atomic mass of “Pennium.”
Average atomic mass = total mass of 20 pennies divided by 20
4) Was the mass of 20 pennies equal to 20 times the mass of one penny? Explain.
5) Explain why the atomic masses for most elements are not whole numbers.
6) How are the three isotopes of hydrogen (hydrogen-1, hydrogen-2, and hydrogen-3)
alike? How are the different? (You may use the image below to help you)
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