NationalGeographic.com [an error occurred while processing this directive]


 
Resources
Date

Delve deeper into hot topics featured in NGM's May Geographica and Who Knew? with help from Resources. Click on a link, pick up a periodical, browse through a book, and explore!
The Book Guy
Grey TabMore Book Guy
GeographicaWho Knew?
Geographica
Chemistry

Ties That Bind
Water is weird—thanks to the hydrogen bond

Just because water is everywhere—percolating through the ground, hovering in clouds, sloshing around our cells—doesn't make it any less weird.
 
Water dissolves a lot of the basic rules of chemistry. Most substances get denser as they turn from liquid to solid form, their molecules stacking up neatly like boards in a woodpile. But water doesn't do that. If it did, the ice cube in your drink would sink. Water expands when it freezes, forming latticelike structures with lots of gaps
between molecules. Instead of a woodpile, ice molecules are more like a house.
 
Squeeze most solid substances in a vise, and they become denser solids (or break into pieces). Squeeze ice in a vise and it gets denser by turning to a liquid. Release the pressure, and the water turns back into ice. The principle works with glaciers: The weight of the glacier creates a liquid layer at the bottom that helps the glacier to slide.
 
Another anomaly: Water has a higher boiling point than many other substances. It's a good thing too. If water had a lower boiling point, the oceans would long ago have evaporated into the atmosphere, and Earth would be a lot more like Venus.
 
Scientists think they know the main reason for water's peculiarity: the hydrogen bond. Admittedly this concept is not the most evocative in the annals of science, but perhaps it's all in the inflection. Try saying suavely, "Bond. Hydrogen Bond."
 
A water molecule will typically link up with four others via this bond—each of the two hydrogen atoms in water grabbing an electron pair in different, nearby water molecules. These bonds have just the right amount of stickiness. It's a Goldilocks situation. You wouldn't want the bonds to be too weak, because water molecules would break apart and would be essentially useless. And if they were too strong, says chemist Martin Chaplin, "you wouldn't get much flow, and water would behave more like glass." Chaplin studies the way the hydrogen bonds in water affect biology. Think about what life is: ordinary matter in a highly organized state. Where does the organization come from? Chaplin suspects the hydrogen bonds in water. Liquid water may seem loosey-goosey—the way it feels, splashes around, drips, puddles, forms a bead. But in biochemical terms, these qualities are signs of structure, not of chaos. Chaplin says water imposes structure on the arrangement of proteins in a cell and thus helps organize life itself.
 
Water is the lubricant, the grease that makes biochemistry possible. Water has given us oceans, clouds, rivers, lakes—and it helps shape everything alive on Earth. So the next time you stand on a beach and admire the beauty and vastness of the sea, or marvel at a seashell, remind yourself: It's all brought to you by the hydrogen bond.
 
—Joel Achenbach
    Washington Post staff writer


Web Links

Water Structure and Behavior
www.lsbu.ac.uk/water/index.html
Martin Chaplin's website on water discusses everything from ionization, anomalies, and hydration to the phase diagram of water illustrating at which temperatures and pressures different forms of water—including at least 12 forms of ice—are present.

Why You Can't Have a Snowball Fight on Mars
www.aspsky.org/mercury/mercury/9801/snowball.html
This entertaining and relatively easy to understand article was written by Scott Sandford, an astrophysicist at NASA Ames Research Center with an expertise in cometary and interstellar ices.

Melting Below Zero
www.bushwalking.org.au/FAQ/FAQ_MeltBelowZero.htm
Adapted from an article in Scientific American, February 2000, by John S. Wettlaufer and J. Greg Dash, this is a great exploration of the concept of surface melting and its affect on winter sports, frost heave, and hail.

The Chemistry of Water
www.biology.arizona.edu/biochemistry/tutorials/chemistry/page3.html
The University of Arizona Biology Department presents a clear, one-page tutorial explaining the polarity of water, hydrogen bonding, and how water helps other molecules dissolve in a solution.  Click through the rest of the site for more information on other aspects of biochemistry.

Bad Chemistry
www.princeton.edu/~lehmann/BadChemistry.html
As stated by the site itself, its purpose is to "bring to light commonly mistaught concepts in the field of chemistry."  Bad Chemistry is part of a larger site entitled Bad Science; both work to correct common misconceptions with to-the-point explanations and simple diagrams.


Free World Map
Bibliography

Allaby, Michael.  Water: Its Global Nature.  Facts on File, 1992.
 
Ball, Philip.  H2O: A Biography of Water.  Weidenfeld & Nicholson, 1999.
 
Bloomfield, Louis A.  How Things Work: The Physics of Everyday Life.  John Wiley and Sons, Inc., 1997.




Top


© 2004 National Geographic Society. All rights reserved. Privacy Policy       Advertising Opportunities       Masthead