Water and the Water Molecule
A short lesson on water molecules designed for
the Junior High science curriculum.
This lesson will…
 Define the term


molecule.
Outline the formation of
a water molecule.
Introduce the
characteristics that make
water so unusual.
Image retrieved from: http://www.accs.net/users/kriel/chapter%20seven/water%20polar.gif
Before we start, let’s quickly
review the definition of an atom.
An atom is the smallest
possible particle of a
chemical element.
Electron
(-)
Nucleus
(+)
Hydrogen Atom
The Molecule
 A molecule is a group of two or more atoms
held together by chemical bonds.
 Water is a molecule.
 Ever hear someone call water, H2O?
Chemical Bonds
Definition:
The energy relationship between two or more
atoms that hold them together.
 Chemical bonds are formed when electrons are
shared between atoms or moved from one
atom to another.
O
H
H
We call it H2O because water
molecules are formed when electrons
are shared between two Hydrogen
atoms and one Oxygen atom.
The Water Molecule
 The angle formed by


the 2 Hydrogen atoms
and the 1 Oxygen atom
is about 105°.
Water molecules have a
positive (+) and
2negative (-) end.
This makes it attract to
other water molecules.
+
H
O
105°
H
+
Hydrogen Bonds
 Hydrogen bonds form
Hydrogen Bond
when the positive (+) end
(the H atom) of one water
molecule is attracted to the
negative (-) end (the O
atom) of another water
molecule.
Cohesion & Adhesion
 Hydrogen bonds influence the properties of water by
allowing individual water molecules to stick to each
other. This is called cohesion. Cohesion gives water
it’s surface tension.
 Ever see an insect walk on water?
 Adhesion allows water to stick to solid materials and
make them wet.
Water
 The most abundant molecule of earth.
 About 70-75% of the earth’s surface is liquid
and solid water.
 Water molecules are also found in our
atmosphere in the form of vapor.
 The only pure substance found naturally in all
three states of matter – liquid, solid, gas.
About the Author
Mark Riley is a second year
graduate student in the
Curriculum & Instruction
program at Ohio University.
Please contact him by email
at mr389997@ohio.edu
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References
Garrison, T. (2006). Essentials of Oceanography (4th ed.)(p. 108).
Belmont, CA: Thomson Brooks/Cole.
http://en.wikipedia.org/wiki/Water_(molecule)
http://en.wikipedia.org/wiki/Molecule