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MAKING A SPLASH >> Chains that pool
3-D Photo of Water Molecules.

Three models for the structure of water molecules. Each individual H2O molecule is linked to four of its neighbors in many current models of the liquid (depicted on left). New results suggest most water molecules are linked strongly to only two others, however. This implies that liquid water molecules may be arranged in rings (middle) or chains (right) that are clustered together by additional, weaker hydrogen bonds. The oxygen atoms are shown in red and the hydrogen atoms in gray in these H2O molecules.

Credit: Anders Nilsson and Hirohito Ogasawara

Highlights of Water Research “Breakthroughs” of 2004

Chains that Pool

Scientists recently rekindled the smoldering debate about liquid water’s structure. According to Anders Nilsson, a professor at Stanford University, “lots of ideas and theories about water are floating around.” However, even though some of the reigning hypotheses reached dogma status, supporting experimental evidence is limited. So Nilsson’s group, testing conventional wisdom, set out to acquire new data.

The team took snapshots of interacting water molecules using high-powered x-rays. Although the technique they used is old, its application for this purpose is new, and the conclusions were surprising. Traditional models predict that each water molecule should form strong hydrogen bonds with four others (see image figure). However, Nilsson’s group found that most water molecules form strong bonds with only two others. If verified, the team’s results suggest the tidy water molecule network depicted in most chemistry textbooks is inaccurate. Instead, they propose that water might actually form a loose network of rings and chains. The debate will likely continue, however, as recent x-ray experiments analyzed by a different laboratory reinforce the prevailing view of water’s structure.

Next: MAKING A SPLASH >> Ions and Interactions

A Special Report The Chemistry of Water