136
APPENDIX
Some Special Properties of Water
The characteristics of water which is so essential for life can be understood by
its (molecular) structure. Because of the electron-pair repulsion, a water
molecule has a V-shape, with oxygen at the apex and the hydrogen on the either
side, which lends its distinct characteristics that it not have in any other shape.
When water is heated up, the individual molecules begin to increase their
motion and move in many different ways. They fly across the room faster and
become of its V-shape. Water can always vibrate - and rotate - and these
additional modes of motion allow water to absorb lot of heat energy without
much change in temperature. This property of water is essential for human
body consisting of two-thirds of water to insulate against the summer heat and
cold winter.
[Smithsonian Science Series 101 - Chemistry by Denise, Kiernan and Joseph
D'Agnese] - Harper Collins Publisher.
Unlike other liquids water has some special and unique physical and chemical
properties which help in sustenance of life. These special properties are :
Density :
Water is the only liquid which expands when freezes. Maximum
density of water occurs at 4
0
C, below or above which water is lighter. Thus ice
floats on water and we find water below the frozen lakes/oceans. Thermal
stratification in lakes is the result of this special density characteristics of water
rendering the aquatic life's survival in a frozen lake. Water in liquid form enters
into the joints, fractures and fisoures of the rocks and during winter when water
is frozen, it expands exerting pressure on the rocks, facilitating weathering
process.
Melting and Boiling Point
Boiling point of water is higher than most of the liquids and the difference in
boiling point and melting points is very high, rendering it possible for water to
remain in liquid state in most parts of the globe.
