WATER MOLECULE

Looking at a water molecule

by Steve Horstmeyer, Meteorologist


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GREATLY ENLARGED WATER MOLECULE

Looking very much like the shape of Mickey Mouse

Water Molecule

Because a water molecule has a slight positive charge on one end and a slight
negative charge on the other...the attraction of the opposite charges, (electro-static charges)
creates what is called surface tension, the weak attraction is called a hydrogen bond.

WATER MOLECULES AT THE SURFACE IN A GLASS OF WATER

Water molecules at the surface

Please note that the illustration above is a gross simplification, the molecules are in constant
motion and it would be rare for this very simple situation to occur exactly as above.
The effect over a sufficiently long period of time is for the attraction of positive and negative
charges to create a surface harder to penetrate than if surface tension did not exist.

This is the reason, if your take care, that you can float a needle or razor blade on
the surface of the water. Surface tension is not the only reason the needle will float, in addition
Archimedes' Principle plays a role.

Archimedes' Principle - If the weight of water, displaced by a object is greater than (or equal to) the weight the object
placed in the water (or any fluid for that matter) the object will float.

CLOUD DROPS WITHIN A CLOUD

Water molecules at the surface

Again the illustration is a simplification. A water molecule inside the drop is attracted equally in all
directions by neighboring molecules. A molecule at the surface is pulled inward, but not outward because there are no
water molecules to pull the surface molecule outward. So....a molecule from the interior of the drop must do work
against the "cohesive" forces (forecs of attraction) between water molecules.

To minimize the amount of energy expended in creating a surface a mass of water will assume the shape that gives
minimum surface area. That shape is a sphere. We say it has minimum surface area to volume ratio. For a small
amount of water, the electro-static forces are stronger than external forces, like air turbulence and gravity. As
the amount of water increases and the drop grows it will be deformed subject to the external forces which can
overwhelm the electrostatic forces.


(CLICK HERE FOR MORE ON WATER DROP DEFORMATION IN THE ATMOSPHERE))
© 2008, Steven L. Horstmeyer, all rights reserved


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