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!
