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Welcome to the Isotope Lab Module

Home Up Isotope Lab Activity Isotopes2002 real elements

You have learned that an atom consists of a nucleus of protons and neutrons, surrounded by a cloud of electrons. You have also learned that the atoms of an element have the same number of protons (same atomic number) in the nucleus.

The mass number of an atom is the sum of the number of protons and the number of neutrons in the nucleus of an atom. The mass number of an atom is almost equal to the mass of its most common form, expressed in atomic mass units (amu).

If you know the mass number and the atomic number of neutrons of an atom, you can calculate the number of neutrons. The number of neutrons is equal to the atomic number subtracted from the atomic mass number.

Number of neutrons = mass number - atomic number

Not all atoms of an element have the same number of neutrons. Atoms with the same number of protons and different numbers of neutrons are called isotopes.

Boron, atomic number 5 has an average atomic mass of 10.81. This is because some of the atoms have 5 protons and 5 neutrons while others have 5 protons and 6 neutrons. Because the numbers of neutrons in the isotopes are different, the mass numbers are also different.

You use the name of the element followed by the mass number of the isotope to identify each isotope: boron -10 and boron -11.

Because most elements have more than one isotope, each element is given an average atomic mass. The average atomic mass of an element is the average mass of the mixture of its isotopes.

For example, four out of five atoms of Boron are Boron - 11, and one out of five is Boron - 10. Thus, in an average sample of five atoms of boron, four atoms are likely to have a mass of 11 amu. One atom will have a mass of 10 amu. If you measured the mass of these five atoms and added them together you would find that they have a total mass of 54 amu. The average atomic mass of the born mixture is 54 amu divided by 5 atoms or 10.8 amu. That is, the average atomic mass of the element born is 10.8 amu.

Isotope Lab Report


Now it is time to conduct an investigation about isotopes. Obtain an Isotope Lab sheet or down load it here. Once you have completed your lab report your groups results to activity 4 to your teacher.


Compare your data collected for activity 4 with that of your class and the entire grade level. Click here to see the class and grade level data sheet.


Design a procedure on your own for determining the atomic mass of some real elements. Use the activity four as a model for your procedure. Obtain a "model" of a real element and use your procedure to determine the abundance of each isotope (colored beads) and the average atomic mass of your substance. Once you have determined the average atomic mass, compare your answer to the real periodic table and determine what the element is that is modeled by your sample. repeat this activity at least four times with different element samples provided.


Analyze your data on the "Jacksonian element" and compare it with the class and 8th Grade data available on the above link.


Analyze your data about the "real element" activity and compare it with this chart. Write a lab report that includes your data tables, procedures and an analyses of your data. Click here to obtain "real element data"

Now that you have obtained your data on the isotopes of various elements, it is time to write a lab report. Click here to see a sample lab report.

Here are a few great web pages to help you:

Chemistry Web Sites Description
This is an online web site to view and gather information on each of the elements found in nature. This is a great resource.
A great web site that teaches about various chemsitry concepts.
Check the periodic table out and search the site for information on the elements.
bulletLos Alamos Periodic table ****
Packed full of information for students as they research the Periodic Table.
bulletChemical Elements
A web site with much information about the elements and the Periodic Table.
bulletEnvironmental Elements
A web site that is chock full of information, especially information on environmental concerns dealing with chemistry.
bulletChemistry at
Information abounds at this web site.


This page was last updated on: 09/05/03