| The water molecule is
asymmetrical, where the two hydrogen atoms are attached to the oxygen atom
like the big feet to the body of my little waterman perched above. This makes
the molecule positive on the hydrogen side (the feet), and negative on the oxygen side
(the head).
Put lots of these lopsided, "magnetic" molecules together, and they will
form intricate structures. Up to about 40deg C,
water really is mostly H4O, a tetrahedral structure with four triangular
sides. Two hydrogen atoms belong to the first O atom, while the other (2) H
are shared with the neighboring O atom, which shares (2) H atoms with its
neighboring O atom, which shares .... etc etc, making up the lattice
structure of water.
All molecules are constantly moving. Heating the
water increases this motion, straining the hydrogen bonds. Heating water
beyond 40 deg C increasingly breaks the hydrogen bonds, breaking the lattice
structure into chains.
All types of water intrusion will be more severe the
warmer the water, since the warmer water molecule is smaller. Surveying
boats with osmotic blisters, for example, I can almost invariably tell which
side normally faced South when in the slip.
To evaporate water, that is, to change it from a
liquid into a gas, requires enough energy to overcome the hydrogen bonds
altogether and allow molecules to escape the liquid. At sea level, it
requires 540 calories of heat to evaporate 1 gram of water.
To evaporate water also requires a vertical moisture
gradient. If evaporated water vapor is allowed to hover over the liquid,
newly evaporating molecules with bounce off and back into the liquid,
preventing further evaporation. To speed evaporation, then, air flow should
be directed over the liquid surface to remove the humid layer (think of your
Spinning class, where you are miserably hot until someone turns on the
fans). The dryer this air is, the more it will increase the vertical
moisture gradient, the more it will speed evaporation (if only someone would
open the door to the Spinning room!).
The stick-to-it-ness of the water molecules creates
surface tension, makes water form beads, and causes capillary action,
where water "climbs" the fibers of a paper towel, until gravity gets
stronger than the hydrogen bonds.
And one last law to remember: |
