WATER, THE ESSENCE OF LIFE
INTRODUCTION
Water is one of the most abundant substances found on the Earth’s surface.
Seventy one percent of the Earth’s surface is covered by water, it is estimated that there
are 326 million cubic miles of water in existence on Earth today. Life itself probably
evolved in the great oceans of Earth more than four billion years ago. If life as we know
it is to be maintained on the planet Earth we must preserve and protect the quality of our
water and what makes it special.
The unique physical and chemical characteristics of the water molecule are one of
the most important phenomena which have allowed life to exist on our planet. Every
living thing on Earth, from the great Blue Whale and the giant Sequoias to the smallest
microbe depend on water to carry on their life processes.
The water molecule is composed of two hydrogen atoms and one oxygen atom.
These atoms are bonded together covalently by sharing electrons. Because the oxygen
atom is much larger and has a greater attraction for the electrons, the electrons are shared
unevenly. The molecule is also asymmetrical in shape. These two factors make the water
molecule a polar molecule with relatively strong negative and positive poles. The polar
nature of the water molecule allows it to form hydrogen bonds with other water
molecules. This attraction (hydrogen bonding) accounts for many of the properties of
water. For example, water is the only substance that exists free in nature in all three states
(solid, liquid and gas,) it has a high boiling point and low freezing point, it has a viscosity
which increases as temperature is lowered, a strong surface tension, a relatively high
density to support animals with no or delicate skeletal systems, a heat capacity which
maintains relatively stable and slow changing internal temperatures, both it’s density and
surface tension increase when substances are dissolved in it, and last but not least, is
water’s ability to dissolve most substances.
THE SURFACE TENSION OF WATER
Background Information
Surface tension is one property of water that is dependent upon the attraction of
its polar molecule. Many organisms depend on the surface tension. Many insects use the
thin film formed by surface tension to keep them from sinking beneath its surface.
Plankton depends on surface tension to help keep it at the surface where there is
sufficient light for photosynthesis, an ample food supply, and warmth for eggs to hatch.
Surface tension is the result of polar water molecules being attracted to each other. Each
molecule is attracted to other molecules that it is in contact with.
The molecules at the surface have electrons on only one side with which to
interact this causes an uneven pulling which creates the effect of a film across the surface
of the water. Small droplets have less volume than large amounts of water. Within each
drop of water the attraction tries to pull the molecules into a form that has the smallest
amount of volume, this is why water “beads up” on newly washed cars or clean waxed
surfaces. The action of soaps and detergents destroys this property by interfering with the
hydrogen bonding. The following are a series of simple activities which can be used to
demonstrate some of the unique properties of water.