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National Science Foundation
MAKING A SPLASH >> Ions and interactions
Photo of sea spray.

Sea spray forming on rocks off Asilomar Beach, California. Seawater contains high levels of salt and other dissolved substances. Recent studies indicate that salt contained in sea spray droplets may play an important role in atmospheric chemistry.

Credit: PDPhoto.org

Ions at the Edge

In 2004, scientists tackled the question of where ions—charged particles such as chloride from the salt sodium chloride (Cl - of NaCl), for example—go in a body of water. Conventional wisdom says the surface layers of water repel ions, which are abundant in salty seawater. Consequently, scientists thought such molecules might get buried, going deep into the interior of solutions. But new experimental and computer-generated models from several different research teams indicate the current thinking is wrong. Although they disagree on some of the details, everyone involved concludes that at least some ions are present in the surface layers of water particles. And where there are accumulated ions, chemistry can occur.

In fact, exposed ions on the ocean surface and in aerosols could potentially bind and react with all sorts of chemicals from the atmosphere. Consequently, fog and ocean spray droplets may be more chemically reactive than previously thought. Indeed, recent atmospheric research indicates that is the case. For example, reports suggest that two ions found in seawater—bromide and chloride—trigger chemical reactions that destroy ozone in the Arctic atmosphere. These destructive but natural events occur after wind and waves deposit the chemicals on polar ice and expose them to sunlight. If the 2004 results hold up, atmospheric chemists who have long ignored the contributions of surface ions when modeling conditions such as air quality will have to rethink their calculations.

Water Chemistry

During chemical reactions, molecular parts ranging from tiny subatomic particles like electrons to entire atoms such as hydrogen get shuffled around, transferred, shared and exchanged. Because H2O is the most common chemical solvent on earth, such changes typically require transport through water. However, water is not simply a passive medium in chemical reactions. In fact, it plays an active role, constantly making and breaking chemical bonds around reactive molecules in order to shuttle them from one compound to another. Scientists still don’t precisely know how water accomplishes these tasks. But researchers have developed new tools for isolating and tracking small electron- and hydrogen-containing water clusters to probe these interactions more easily.

The results shed light on a range of extremely common reactions that involve electrons and hydrogen atoms. For example, the oxidations that rust cars and age your skin both involve the exchange of electrons in water. The microbe-fighting and pH-balancing chemistry that keeps swimming pools clean relies on a delicate interplay of electron exchanges and hydrogen transfers. To improve models used in a range of applications, scientists need to understand the fine details about water’s role in chemical reactions such as these. Progress in this area would likely impact a range of fields—from the study of complicated events such as protein folding to the improved design of pharmaceuticals.

About 50 NSF-supported investigators are currently exploring the fundamental properties of water. Understanding the chemistry of water in its many forms is still considered a major scientific challenge. However, if the remarkable progress of new research is any indicator, this challenge will be met.

Links to selected researcher’s sites:
Anders Nilsson, Stanford University
Heather Allen, Ohio State University
Geraldine Richmond, University of Oregon
Mark Johnson, Yale University
Dan Neumark, University of California, Berkeley
Ahmed Zewail, California Institute of Technology
Atmospheric Integrated Research for Understanding Chemistry at Interfaces, University of California, Irvine (AirUCI)

Next: Water's Many Forms

A Special Report The Chemistry of Water