A Sticky Molecule
BACKGROUND
Water is one of the simplest substances on Earth, and yet we must have it to live. A
person can survive only about three days without water. Water is so common that we
often ignore some of its characteristics. Pure water is clear with no odour or taste.
These are three obvious properties of water, others are less obvious. For example,
compared to other liquids, it takes a lot of heat to make water hot and even more to
make it boil.
Knowing the molecular structure of water – or any other substance – helps in
understanding many of its properties. In every water molecule, two hydrogen atoms are
joined to one oxygen atom by forces called chemical bonds. The chemical bond
between hydrogen and oxygen happens when the two atoms share electrons between
them – one electron from hydrogen and one from oxygen.
In this activity, you will learn how hydrogen and oxygen join to investigate some
characteristics of the bond between them. This will help you understand the properties
of water – many of which you will investigate in other activities.
PROCEDURE
1. Locate the “Water Molecule Pattern Sheet”.
2. Colour both the hydrogen atoms and the nuclei blue. Leave the electrons
uncoloured.
3. Colour the oxygen atom and the nucleus red. Leave the electrons uncoloured.
4. Cut out all the pieces (atoms, nuclei, and electrons) of the water molecule.
5. In every water molecule two hydrogen atoms are bonded with one oxygen.
Before gluing the hydrogen atoms to the oxygen atom try different arrangements
and use blank paper to sketch at least THREE (3) different ways that the two
hydrogen atoms and one oxygen atom could be joined as a single molecule.
6. Early last century, scientists discovered the actual shape of a water molecule.
The hydrogen atoms were attached to the oxygen atom in a way that looks a lot
like the head of a mouse (oxygen is the head and the hydrogen atoms are the
ears). Based on this description, glue the hydrogen and oxygen atoms together.
The glue represents the bonding between the atoms.
7. Glue a nucleus in the center of each atom so that the nucleus covers the letter
representing the atom.
8. You should have 10 electrons:
a. Glue to of these to the oxygen atom, placing them on opposite sides on
the dashed circle.
b. Remember that each bond between hydrogen and oxygen is formed by
sharing two electrons. At each place where the edge of the hydrogen
atom crosses the edge of the oxygen atom glue two electrons.
c. Glue the rest of the electrons (4 remaining) to the oxygen atom, spacing
them evenly around the solid outer circle.
9. Because of the way hydrogen and oxygen bond, each hydrogen atom has a
slightly positive charge, and the oxygen has a slightly negative charge.
a. Draw a (-) sign on the oxygen atom and a (+) on each hydrogen atom.
QUESTIONS – answer in FULL SENTENCES
1. Name the elements found in a water molecule?
2. What is the ratio of hydrogen atoms and oxygen atoms in a water molecule?
3. A molecule is a combination of atoms that are bonded together. How are oxygen
and hydrogen atoms of a water molecule held together?
4. Describe the location of the charges on YOUR molecule. This makes water a
polar molecule. Think of a magnet to describe a polar molecule.
5. If one object has a positive charge and one has a negative charge, what will they
tend to do to each other?
6. Using your answer to Question #5, why do you think water molecules tend to
stick together?
7. Sketch at least two different ways that two water molecules could be positioned
so that they stick together?
8. Explain why you think a lot of heat is required to warm up and boil water?