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LAB ACTIVITY CALCULATING ATOMIC MASS
Element 114 – Vabeachium
Press Release from the Virginia Beach News:
Virginia Beach, VA- Chemists, working on a project for the city of Virginia Beach, have recently discovered what is
believed to be element 114. The researchers have proposed that the element be named vabeachium (va-beach-e-m), after
the city in which it was discovered. The proposed element symbol is Vb.
Samples are currently being distributed to all of the local high schools. Each school is to isolate the individual isotopes,
determine the relative abundance of each isotope, and calculate the atomic mass of the new element.
Two properties unique to vabeachium should make the work particularly easy – vabeachium atoms are visible to the
naked eye and each isotope has a slightly different color.
Introduction
The atomic mass of an element must reflect both the masses of each isotope of the element and the relative abundance of
the isotopes of the element. Mass number is the total number of protons and neutrons in the nucleus of an atom; the mass
number can be used as the mass of the isotope. Atomic number is the number of protons in the nucleus of an atom.
Atomic mass is the weighted average of the masses of the isotopes of the element.
Materials: Numbered samples of vabeachium.
Procedure
1.
2.
3.
4.
5.
Obtain a numbered envelope that contains a sample of vabeachium.
Count the total number of atoms. Record this value in your data table.
Since each isotope has a unique color, separate the isotopes of vabeachium.
Write the name of the isotope in the data table, using the element name and the mass number (vabeachium-275).
Count the number of atoms of each isotope. Record the quantities in your data table. (Remember, significant figures
are not determined by counts.)
6. The numbers of protons, neutrons and electrons in each isotope are written on the front of each atom. Calculate the
mass number for each isotope. Record the mass number for each isotope in your data table.
7. Return the atoms to the envelope and return the envelope to your teacher.
Data Table
Isotope
1
_______________
2
_______________
3
_______________
# of atoms
% abundance
Mass number
Total number of atoms of vabeachium in the envelope ________________
Calculations
1. Calculate the percent abundance of the first isotope.
2.
number of atoms of the isotope x 100% = % abundance of the isotope
total number of atoms in the sample
3. Record the % abundance in the data table, rounding the value to 4 significant figures.
4. Repeat this calculation for each isotope.
5. To calculate the mass that each isotope contributes to the weighted average, multiply the % abundance (in decimal
form) of one isotope by the mass of one atom of that same isotope (represented by the mass number). Repeat this
calculation for each isotope.
Isotope 1 (% abundance x mass of 1 atom) = __________ x _________ = __________
Isotope 2 (% abundance x mass of 1 atom) = __________ x _________ = __________
Isotope 3 (% abundance x mass of 1 atom) = __________ x _________ = _________
6. To calculate the weighted average atomic mass of vabeachium, add the values obtained in #5.
Atomic mass of vabeachium = ___________
Extra Credit:
1) Determine the mass numbers for the following SIX isotopes:
Percent Abundance
Mass of Isotope (relative abundance)
0.011%
0.021 amu
0.796%
1.53 amu
32.96%
63.94 amu
33.86%
66.03 amu
25.36%
49.61 amu
7.22 %
14.30 amu
2) Determine the atomic mass from data above.
3) Name this element, if there are 117 neutrons.