PERIODIC TABLE AND ISOTOPES
This laboratory exercise consists of two parts: Investigating the periodic table and
PART 1: INVESTIGATING THE PERIODIC TABLE
Dmitri Ivanovich MENDELEEV, a Russian scientist, was able to organize the elements
into a system based upon first grouping the known elements by similar properties and
then ranking by INCREASING ATOMIC MASS. Mendeleev was very bold for his time.
His periodic table was such that he could predict elements not yet discovered and give
properties of those elements based on the position of the missing element in the
In the FIRST PART of this laboratory exercise you will become a scientist in the year
1869. The known elements are written out on cards with properties of each element.
The goal is to group the cards by oxygen combination properties and then rank the
cards by increasing atomic mass. The final steps will be to expand the table into the
PART 2: INVESTIGATING ISOTOPES
ISOTOPES are ATOMS of the same atomic number having different masses due to
different numbers of neutrons. The ATOMIC MASS of an element is the weighted
average of the masses of the isotopes of that element. The weighted average takes
into account both the mass and the relative abundance of each isotope as it occurs in
nature. The RELATIVE ABUNDANCES and masses of small atomic particles are
measured in the laboratory by an instrument called a mass spectrometer. The mass
spectrometer separates particles by mass and measures the mass and relative
abundance of each. From these data a weighted average is calculated to determine the
atomic mass of the element.
In the SECOND PART of this laboratory exercise you will carry out experiments and
perform the necessary calculations to determine the atomic mass of the fictitious
element vegium. The three different isotopes of vegium are black bean, brown bean,
and green pea. As in real elements, these isotopes are collections of particles having
different masses. Your job will be to obtain a sample of vegium and determine the
relative abundance of each isotope and the mass of each type of particle. From this
data you will calculate the weighted average mass, or atomic mass, of vegium. Unlike
real isotopes, the individual isotopic particles of vegium differ slightly in mass, so you
will determine the average mass of each type of isotopic particle. Then you can
calculate the weighted average mass or "atomic mass" of vegium.
The laboratory objectives for this experiment relating to the periodic table and isotopes
1. Gaining familiarity with the elements and the periodic table.
2. Organize element cards similar to how Mendeleev categorized elements on his
3. Determine the average masses of each isotope of the fictitious element vegium.
4. Determine the relative abundances of isotopes of vegium.
5. Calculate from experimental data the atomic mass of vegium.
The text addresses topics that are related to the experiment in chapter 5, Atomic
1. 5.4 Goal 4
2. 5.5 Goals 7, 8
3. 5.6 Goals 9, 10
Suggested exercise at the end of chapter 5, starting on page 130.
Section Problem #
5.6 20, 21, 22
This experiment will require the use of the following glassware/hardware:
2. Glue sticks
3. Misc. small beakers
This experiment will use the following chemicals:
1. Vegium sample containing black beans, brown beans, and green beans.
Calculating The Atomic Mass of fictitious element marbelium:
Blue Red Green Total
1. Mass of each isotope 16.800 g 12.750 g 23.520 g 53.070 g
2. Amount of each isotope 35 25 48 108
3. Average mass of each isotope 0.48000 g0.51000 g0.49000 g1.48000 g
4. Relative abundance of each isotope0.32 0.23 0.44 0.99
5. Relative mass of each isotope 0.15 g 0.12 g 0.22 g 0.49 g
6. Percent abundance of each isotope 32% 23% 44% 99%
7. Average atomic mass of the fictitious element marbelium = 0.49 amu
1. MASS OF EACH ISOTOPE: is determined experimentally from the sample of
marbelium being investigated.
2. AMOUNT OF EACH ISOTOPE: is determined experimentally from the sample of
marbelium being investigated.
3. AVERAGE MASS OF EACH ISOTOPE:
4. RELATIVE ABUNDANCE OF EACH ISOTOPE:
5. RELATIVE MASS OF EACH ISOTOPE:
6. PERCENT ABUNDANCE OF EACH ISOTOPE:
7. AVERAGE ATOMIC MASS OF THE FICTITIOUS ELEMENT MARBELIUM: