BACKGROUND:
Students have learned that the hydrogen
and oxygen in water is held together by a covalent bond, which refers to
the sharing of electrons. Water has a more specified bond called
a hydrogen bond, which allow water molecules to join together in a tight
structure. All this tightness of bonding accounts for many of water's
remarkable properties. Hydrogen bonds account for the unusual cohesive
power shown by water's high surface tension. It also explains the
ability of water to adhere strongly to a wide variety of substances thereby
"wetting" them. Students do not have to remember all these properties,
but the key objective is for them to understand that how water molecules
"hold hands" plays an important part of how water reacts.
Many students may have heard about the Titanic.
On its maiden voyage from England to the United States, the unsinkable
ship hit an iceberg and sunk in the early 1900's. Many stories have
been written about the lives of the rich and famous who perished on that
voyage. But how could ice cause so much damage?
When temperature decreases, the bonding of
the water molecule becomes strong and prevents the molecule from contracting
or shrinking. At 4°C the molecules begin to arrange themselves
along the directional lines of the bond, leaving gaps or openings between
these bonds. The water expands until at 0°C, it solidifies in
a structure which is a very open crystalline structure. The same
general pattern occurs during the formation of snowflakes, which are branching
ice crystals grown out of moist air. Snowflakes have a hexagonal,
or six-sided, structure, the outline which is formed by the bases
of six tetrahedrons.
Water is a weird and awesome substance!
PROCEDURE:
- Have the students research
icebergs, which is ice that floats in the oceans. Only fresh water
will freeze, so the ice in icebergs is salt free. Ice is actually
less dense than liquid water because of how the molecules "freeze."
Use the internet and use a search engine to find out more information.
- Students may be interested in learning
more about Titanic. They are probably curious on how a big
ship could not see the danger of an iceberg. If you look at the worksheet,
you can see the bulk of the iceberg floats under the water, so a ship could
hit the iceberg without running into the portion that is above water.
- Students can color the iceberg and
write a story on the iceberg that brought down the Titanic.
