Basic Molecular Theory
- 3-D model of a water molecule
- Diagrams of various molecules
- Review the basic atomic theory with the students.
- Tell the students atoms are "building
blocks" for other things.
- Explain that when atoms of different elements
bond together they form molecules. (A molecule
is the simplest unit of a compound, which will
be discussed in the next lesson).
- Show the students the illustration of a water
molecule. Tell them that water is made of the
element hydrogen and the element oxygen. When
two atoms of hydrogen join with one atom of
oxygen the molecule formed is water.
- Say, "It is written this way" and
write it down for the students while explaining
the breakdown. "H2O" (hydrogen = 2
atoms and oxygen = one atom).
- If you like you can comment on the interesting
fact that both H and O are gases but when joined
they form water, which can exist as a solid,
liquid or gas.
- Show the students diagrams of other molecules
to encourage further discussion.
- To illustrate molecular theory, use marshmallows
(or peas) and toothpicks to construct molecular
models. The toothpicks serve as the "invisible"
bonds between the atoms (marshmallows).
- Try the following experiment, which demonstrates
that molecules are constantly moving.
- A glass of water
- Food coloring
|Place a drop of food coloring in
the water. Don't move the glass but watch closely
for a few minutes.
|The intense color eventually moves
through the water to become a uniform, paler color.
|Molecules are always moving, so when
the food coloring molecules are added to the water
molecules they bounce around amongst each other
and eventually become evenly distributed throughout
the glass. Due to the colorless nature of the water
it is easy to watch this process happen.
Did You Know?
- The number of teaspoons of water in the Atlantic
Ocean is equal to the number of molecules in
a teaspoon of water.
- There are over 10,000 types of molecules in
- There are 10 times as many carbon-based molecules
than all other elements combined. This is largely
because carbon atoms bond so well with each
other. Organic chemistry is the study of carbon-based
- One of the largest molecules, a giant in its
own way, is DNA. It has the unique ability to
replicate itself. It may be 10,000 times longer
than the chromosome it is contained in, so is
very tightly coiled in order to fit. If stretched
out, the DNA in a single human cell would reach
approximately two meters and if all of the DNA
in one person were uncoiled and placed end to
end, it could encircle the Earth 700,000 times.
- Some DNA molecules consist of over 1 billion