The water molecule is made up of two hydrogen atoms and one oxygen atom bonded at an angle of 105 degrees, giving water its polarity and ability to form hydrogen bonds between molecules. This hydrogen bonding allows water to absorb large amounts of heat without significant temperature change and exist in solid, liquid, and gas forms, unique properties important for moderating climate and sustaining life. Water's high heat capacity and heat of vaporization require significant energy input to change its state, slowing boiling and cooling.

1. Water Molecule 1/1/10 5:21 AM
Water Molecule
The Water Molecule and its Properties
The water molecule is formed from two hydrogen atoms and one oxygen
atom. The bonding angle of the two hydrogens is almost 105 degrees rather
than 180 degrees which would make the molecule symmetrical. This causes
it to be dipolar, giving it a positive and negative side which accounts for its
unique properties. This allows the formation of hydrogen bonds between
adjacent molecules. There is a weak intermolecular force of electrostatic
attraction between the molecules which is known as van der Waals force.
This causes the molecules to act as larger units than the individual
molecules.
Water is a very unusual compound; it is very common and is found in all
three conditional states, solid (as ice), liquid (as water) and gas (as water
vapor). Other types of bonding can occur, such as covalent bonding (as seen
in the formation of molecular oxygen) or ionic bonding (as seen in the
formation of salt or sodium chloride[NaCl]). Hydrogen bonding can break up
the electrical attraction of atoms of solids and dissolves them.
http://www.aquadyntech.com/watermolecule.html Page 1 of 2

2. Water Molecule 1/1/10 5:21 AM
In ice crystals the water molecules are widely separated, while in the liquid
form they are closer together although less tightly bound. Therefore ice is
bulkier and less dense and floats on water. If we compare the freezing and
boiling points of water with what one would predict from extrapolating the
molecular weights of other molecules, we see that it would be predicted to
freeze at -90 degrees C and boil at -68 degrees C. What a different world we
would have. So much for the validity of extrapolation.
The heat capacity of water is high compared to other common materials.
This means that it can absorb or can lose a lot of heat energy without
changing its temperature very much. This buffers the environment against
large, rapid temperature changes. An example is the more moderate climate
of a coastal location compared to one far inland. The diel temperature
change of the surface waters of the oceans (or lakes, or even a swimming
pool) is small compared to the diel temperature change of the surrounding
air. This is due to the high heat capacity of water.
As freshwater goes from ice to liquid or from liquid to gas, it undergoes an
obvious change of state. The amount of heat energy that is required to
change its temperature in the same state is referred to as the specific heat.
Specific heat can be defined as the amount of heat energy required to raise
the temperature of 1gm 1 degree C. It is expressed in calories. A calorie is
defined as the amount of heat required to raise the temperature of 1gm
liquid water 1 degree C. The specific heat of liquid water is 1.0 calories while
it is 0.5 calories for ice. If we look at a graph of temperature versus heat
input, we can follow the change from ice at -100C to water vapor at 150
degrees C. In order to get the ice to the melting temperature, it requires
100*0.5 or 50 calories. To change from ice at 0 degrees C to water at 0
degrees C requires an additional 80 calories (the heat of fusion or melting). It
now takes 100 calories to heat the water from 0 degrees C to 100 degrees C
(100*1). To change from liquid to water vapor at 100 degrees C requires an
additional 540 calories. This is called the heat of evaporation or
condensation. It explains why it seems to take so long to boil water on the
stove when it seems about to boil. If we had a constant heat supply under a
pot at the rate of heating raised to water from, say, 20 degrees C to 100
degrees C in 4 minutes, it would take another 6 minutes 45 seconds to boil
the water. Also remember that when water vapor condenses (as in rain), it
gives up this energy.
Surface tension of water is high. In fact, water has the highest surface
tension of any common liquid except mercury. ( Here are some other
comparisons.) It is the tendency of water molecules to attract to each other
or cohere to each other at the surface of any water. It can be demonstrated
in the formation of a drop of water, of heavier than water objects floating on
the surface or in capillary action in a glass tube.
<- Home | Contact Us | Site Map | FAQ's | Savings | Technical | E-Mail WebMaster ->
392 Keeler Woods Drive Marietta, GA 30064 770-422-6997 Voice 770-424-5912 FAX
This Page Last Updated Mon, 04 Aug 2008 13:58:51 GMT
http://www.aquadyntech.com/watermolecule.html Page 2 of 2