Sandra Soh
TG105
The main properties of water are a result of the combined effect of hydrogen
bonds between molecules of water and the polarity of water molecules due to
stronger electro-negativity of oxygen.
Hydrogen bonds are formed from intermolecular forces of attraction between
the hydrogen end of one water molecule and the oxygen end of a different water
molecule due to the hydrogen end being relatively positive compared to the
oxygen end being negative due to its stronger ability to attract the shared pair of
electrons in the covalent molecule or in other words its stronger electronegativity.
These result in the cohesion and adhesion of water molecules.
Cohesion is when the water molecules are attracted to each other and cohesive
forces between molecules are shared with all neighboring molecules. However
water molecules on the surface do not have neighboring molecules above them
to share the cohesive forces with, hence there are stronger cohesive forces
shared between molecules of water on the surface as they are sharing the forces
only with neighboring molecules on its sides and below it. This results in surface
tension, where water forms a convex shape when its container is filled to the
brim due to the forces of attraction between water molecules. This phenomenon
is significant to living things because it allows small or light objects to float on
water as those objects do not have enough energy or mass to break the cohesive
forces on the surface water and sink into the water. As a result, things like dust
particles do not sink down to the bottom of the ocean, and this ensures that
marine life will not die because of the dust particles and the ecosystem is kept
from destruction by the entrance of a foreign substance.
Adhesion is the attraction between water molecules and another polar molecule.
The positive end of the water molecule is attracted to the negative end of the
other molecule and vice versa. This allows hydrogen bonds to form between
water molecules and another molecule, resulting in adhesion. This is significant
to living things because plants use a combination of adhesion and cohesion for
capillary action. Water is pulled up the xylem vessel by the water molecules
being attracted to the cellulose xylem cell wall and moving up and pulling more
water molecules upward because of the attraction between the water molecules.
This is significant as it is one of the mechanisms used by plants to absorb water
which is a raw material needed for photosynthesis, an important process to
produce food which is consumed or used by all living things.
All water molecules throughout the liquid form hydrogen bonds, hence there are
many hydrogen bonds that need to be formed or broken to change the
temperature of water. This causes water to have a high specific heat capacity,
which means it takes a lot of energy to change the temperature of water. This is
significant as most of the earth surface is made up of water and the high specific
heat capacity of water means that the temperature of earth will not undergo
drastic change easily, allowing for processes of life to carry on as most processes,
especially those involving enzymes only work effectively at a small range of
temperature.
Through these few named examples, it is clear how the different properties of
water are very significant to living things.