Group Members ______________________________________ Period ____ Date ___________
Molecular Modeling of Carbon Compounds
Adapted from an original work by John Banister-Marx, Wright Center for Science Education,
Tufts University, Medford, MA
Introduction:
Atoms in the universe share a fundamental architecture. Formed in the birth of stars since the Big
Bang many billions of years ago, groups of atoms called molecules compose all of matter, including
living things. Life’s atomic structure is not fundamentally different. By creating 3-dimensional models of
organic and inorganic compounds using molecular modeling kits, you will recognize that the types of
atoms that bond together and their arrangement is a result of each individual atom’s arrangement of
subatomic particles. Furthermore, it is the number, type, and arrangement of atoms that gives each
compound its unique set of physical and chemical properties. Life is merely the most splendid of all
atomic creations.
Atoms bond with each other in order to fill their outermost electron shell. This is generally true
for all atoms except the noble gases which have outermost, or valence, electron shells that are already full.
The number of electrons needed to fill this outer shell is equal to the number of bonds (shared pairs of
electrons) formed between atoms. The biochemical magic of carbon, so essential to life on Earth and
probably elsewhere in the universe, lies in the four electrons of its outer shell. Needing four electrons to
fill its outer shell, carbon can form four bonds. Carbon forms covalent bonds by sharing its four electrons
with up to four other atoms. In some cases carbon forms four single covalent bonds: as in methane CH4.
It can also form double bonds (each with two shared pairs of electrons) as in carbon dioxide, with carbon
in the middle and an oxygen atom on each side: O=C=O. Carbon can even form triple bonds as in
acetylene gas: H-C=C-H; and in hydrogen cyanide H-C=N. It is this extremely flexible molecular
architecture that produces the multitude of different organic compounds.
methane
cyanide
acetylene gas
Purpose:
 To discover how the valence arrangement of an atom’s electrons contributes to its tendency to
form covalent bonds.
 To create three-dimensional models of simple inorganic molecules and more complex organic
molecules.
 To relate the chemistry of organic molecules to the stability of living systems on the Earth.
Materials: (per team)
 molecular model kit
 student lab sheet
 print or web-based resources
Procedure:
1. First let’s examine the periodic table using a new concept – ionization energy. An atom’s ionization
energy is simply the amount of energy required to remove an electron from atom when the atom is in
the gaseous state. The periodic table below shows the ionization energy tendencies of the elements.
In general, ionization energy increases as you travel from left to right on the periodic table. This
stands to reason because as you move from left to right the number of electrons in the valence energy
level of an atom increases. Therefore, the closer an atom is to having a full valence energy level and
thus being stable, the harder it will be to remove one of its electrons.
Likewise, ionization energy decreases as you travel down a particular group on the periodic table.
This is because as atoms become larger, electrons on the outermost or valence energy level are farther
from the attractive forces of the nucleus, therefore they can be more easily removed.
2. Recall the seven elements that make up over 99% of the human body. List them. ________________
Circle these elements on the periodic table above.
What generalization can you make about the ionization energies of these seven elements? Is it higher
or lower than most other atoms?
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Based on this generalization, hypothesize what kind of chemical bonds these elements prefer to form.
Ionic or covalent? Explain why. _______________________________________________________
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3. Examine the contents of your molecular model kit. Complete the chart on the next page. Use the
periodic table above to help you.
Element
Bead
Color
Carbon
black
Hydrogen
white
Nitrogen
blue
Oxygen
red
Sulfur
yellow
Halogens (i.e.
Cl, F, Br, I)
green
Group Number
(Roman numeral above each
column in periodic table)
# of valence
electrons
# of electrons
needed in order to
fill valence level
What do you notice about the relationship between the number of electrons needed in order for each
element to become stable and the number of holes on the bead representing that element?
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4. Using one molecular model kit per team, make the following molecules. Draw the shapes of your
verified molecules in the appropriate space in the table. Represent each atom with its chemical
symbol. A line drawn between two chemical symbols represents a single pair of shared electrons (a
single covalent bond). See the drawings on the front page as examples. You may have to conduct
extra research for some of these.
Molecule
(Chemical
formula)
water (H20)
carbon dioxide
(CO2)
hydrogen peroxide
(H2O2)
ammonia (NH3)
Description
the most important
molecule on planet Earth.
Universal solvent
colorless gas consumed
during photosynthesis and
produced during aerobic
respiration and
combustion. greenhouse
gas
a bleach blonde’s favorite
recipe. Also a natural but
poisonous by-product of
cellular metabolism that is
constantly being broken
down in your body by the
enzyme catalase
a base used in cleaning,
and possibly one of the
gases in Earth’s early
atmosphere
Drawing
ethanol (C2H5OH)
the “active” ingredient in
alcohol
lactic acid
(C3H6O3)
the substance that makes
your muscles ache after
heavy exercise
glucose (C6H12O6)
the most important energy
source in living things
DISCUSSION: (answer on a separate piece of paper and attach to this lab sheet)
1. Of what kinds of atoms do most of the molecules that you constructed seem to be made?
2. What kind of bond do these atoms tend to form? Is this type of bond relatively strong or relatively
weak?
3. How might ionization energy be used to predict which elements will form bonds?
4. How might ionization energy be used to predict what type of bonds elements prefer to form?
5. All molecules that contain carbon (except carbon monoxide (CO) and carbon dioxide (CO2)) are
considered to be organic molecules. All other molecules are inorganic. Based on the molecules that
you made and the descriptions of various molecules in this lab would you say that organic molecules
or inorganic molecules are more important to life? Defend your answer with evidence from the lab.
6. Review your answers to the previous questions. What might this information tell us about how life
seems to be able to remain organized (put together) even though the laws of thermodynamics would
suggest that it should fall apart.
7. List two other things that your team learned about molecules from doing this activity.
Work Cited
Banister-Marx, John. "Molecular Models and The Origin of Life." eThemes. University of Missouri, 17
Feb. 2005. Web. 14 Oct. 2010.
Grandinetti, Philip J. "General-Chemistry-Ionization-Energy-Trends." 2010. Web. 15 Oct. 2010.