Water Cohesion, simply put, means that water molecules

Water has extraordinary properties
which makes it vital to life on earth. The earth is composed of 75% water and
in living cells, 75%-90%. Because of the slight 4.5 degrees difference in
water’s expected 109.5 degrees tetrahedral structure, the polar molecule, water
has some amazing properties which makes it evident that life of earth is
dependent of its presence. Hydrogen bonding, Cohesion, Surface tension,
Adhesion, Capillarity Action, Freezing and Density, Heat Capacity and being an
excellent solvent are some of the properties which demonstrates the importance
of liquid water.

Hydrogen bonding is possible since
water is known to be a polar molecule that is, having two charges; oxygen being
of a slightly negative charge and hydrogen a slightly positive. Because of this
and oxygen’s high electronegativity, that is, it’s high affinity for electrons,
the electrons are tend to be shared unequally, hence, bringing forth it’s
polarity. Due to the hydrogen bonds, water molecules can bond to other
surrounding water molecules. The hydrogen bonds are weak since bonds are
constantly breaking and forming.

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As a result of water molecules’
polarity and ability to hydrogen bond it is known to be cohesive. Cohesion,
simply put, means that water molecules are able to adhere to other water
molecules. Because of water’s cohesiveness the inter-related property of surface
tension is recognized.

At the surface of water there are
fewer water molecules to cohere with and hence, the bonds among those molecules
that do come into contact with one another create a layer of strongly bonded
water which makes a bit difficult to penetrate since it creates an invisible
barrier of the water from the atmosphere.

Another amazing property of water is
adhesion. Water is attracted to other molecules via adhesive forces, that is,
attractive forces between molecules of one kind and molecules of a different
kind. Water molecules adhere to other substances as a result of its polarity.
Example: Water in a glass; the water molecules adhere to the molecules of the
glass.

As a result of adhesion and cohesion,
water is able to move to very high heights defying gravity until the force of
gravity overpowers it, this is called capillary action. In capillary action the
forces of cohesion are strong but the forces of adhesion are stronger and hence
the liquid is able to move upwards by being attracted to the walls of the tube
e.g. When a nurse is taking a sample of your blood for a test, after pricking
the finger she uses a capillary tube to collect a sample of the blood (N.B. blood
is made up of about 90% water), it is noticed that the blood goes up the tube.
This is because of the higher attraction of the water molecules to the capillary
tube molecules. Another example is the transportation of water to all parts of
the plants through the xylem; water molecules are attracted to the walls of the
xylem and the water keeps moving upwards due to capillary action and the
transportation of the products of photosynthesis via the phloem which is aided
by water.

Most
substances in their solid form tends to be more dense than when it is in its
liquid form, in the case of water it is the complete opposite. In liquid water
the hydrogen bonds are not fixed, the molecules are free to move around and it
is usually flat or two dimensional but, in ice a crystalline structure is
formed, hydrogen bonding to four other molecules in a three dimensional
lattice, having space between and hence, being less dense. Because liquid water
is more dense than ice, it allows for the continuation of aquatic life even in
very cold temperatures by making the ice float at the top and because of its
white colour, it is able to reflect light and hence continuing life below the
ice since animals are able to survive in the liquid water below the ice.

Water
also, has a high specific heat capacity. This is the amount of heat energy
required to raise the temperature of one kilogram of water by one degree celsius.
Water absorbs a lot of thermal energy before it is converted to another state,
and for this reason it is the medium of life since it is able to regulate and
minimize the change in temperature. E.g. on a very sunny day, the temperature
on land increases but in the water has a very low temperature change, and hence
water’s ability to absorb heat is seen. Water is used by warm-bodies animals to
dispense heat around the body by moving it from warm places to cool places.

Water
is known to be an excellent solvent which means that other substances can
dissolve in it to form solutions. A major and important example is the process
of transportation and excretion in the human body. Water transports all the
essential nutrients in easy to absorb form and also, all the waste products
must be excreted from the body to prevent toxic build-up.

By examining few of these unique
properties of water we begin to appreciate its presence since without it we
would never be present on earth.