Download Nuts,Bolts and Isotopes- Average Atomic Mass Activity

Nuts and Isotope Activity
(Atomic Weight)
Name: _______________________
Date : _______________________
We know that an element is made up of the same types of atoms. Iron is made of iron atoms. The element carbon is made up
of only carbon atoms. However there is more to the story! Elements contain atoms of the same type but not all of the atoms are
exactly the same. Not all carbon atoms are alike! There are three different types of carbon atoms (Carbon 12, 13 and14). Each
type of carbon atom has a different mass. We refer to these atoms which are the same, but different, as isotopes. Isotopes are
atoms of the same type, but with differing number of neutrons.
The average mass (atomic weight) of any element is the average (of the abundance) of all the isotopes that make up that
element. To help you understand this concept better, you are going to do an activity that simulates how the atomic weight of an
atom is determined. In this activity you will be given a sample of 3 types of hardware ‘nuts’. Each nut type represents an
‘isotope’ of a fictional element. You will also notice that each nut type differs in its mass. Also, there is more of one type isotope
or nut than another.
Equipment
(1) 1/4 in stop nut (3) 1/4 in regular nuts (1) 1/4 in wing nut (1) Electronic balance.
Isotopes
Elements are composed of atoms. As mentioned in the previous section each element is composed of the same types of atoms
(for example carbon is composed of carbon atoms). However, not all of the atoms found in that element are the same. For
example, carbon contains three different types of atoms (carbon-12, 13 and 14). Each atom has the same number of protons
and electrons but differing numbers of neutrons. These are referred to as carbon isotopes. Elements are combinations of these
isotopes in differing abundances. When averaged together, they create the average atomic mass or atomic weight of a specific
element. For example the average atomic mass of carbon is 12.011 amu.
In this activity, you will work with 3 different nuts. They are of different sizes and masses. However, you will be given more nuts
of one type, than the other. In other words there are differing abundances of nuts in your sample.
Directions
1. Weigh each nut type (individually and as a group) and record the mass in table 1 (weigh all of the stop nuts together and record,
etc.)
2. Calculate the average mass of all three nuts and record in Table 1.
Table 1
Nut
Individual
Mass of
nut(g)
Stop Nut
Regular Nut
Wing Nut
Average Mass

For the average mass, add the individual masses of each nut and divide by 3.
4. Now calculate the % abundance of each type of nut (use your pre-activity lesson to help guide you) and record in table 2.
Table 2 – Isotope – Atomic Weight (Percentage Abundance)
Mass of each
individual Nut (g)
Nut
% Abundance
(Number of Nut
type/Total
Number of Nuts)
Total (%
Abundance x
Mass of individual
Nut)
Stop
Regular
Wing
Atomic Weight

To find the average atomic mass of the isotopes, use the mass x abundance % formula you learned in previous classes. To
find the % abundance, divide the number of each nut type by the total amount of nuts (for example, you may have 12 nuts
total and 6 stop nuts, so 6/12 = 0.50 abundance of that nut). Next multiply the total abundance times that of the individual
mass of that nut type (Let’s say the stop nut weighs 1.2 g. Multiply 1.2 g x 0.50 = 0.6 g). Finally add up all of the values for
each nut type (Stop nut – 0.6 g + Wing nut – 0.77, etc.). This will give you the atomic weight.
(1). Are the values you got in Table 1 and Table 2 different? Why? Relate this to the masses of different types of isotopes or nut
types you worked with.