- Number 356 |
- February 13, 2012
Mock atoms step up to the scale
For biofuel production, this
study provides scientists with
the information they need to
better predict, manipulate and
control the behaviors of atoms
When studying an atom’s behavior in different environments, scientists rely on electronegativity scales, which describe each atom’s ability to attract and repel electrons. But what about pseudo-atoms, a.k.a. those molecular fragments that behave like atoms by not changing much in various environments? Scientists at DOE’s Pacific Northwest National Laboratory and Heriot-Watt University in Scotland put the tetrahedral ammonium radical, made from a nitrogen atom and four hydrogen atoms, on the electronegativity scale. It has the same attractive force as potassium and the same size as a rubidium atom.
With this information, which will be incorporated into textbooks and reference books, scientists can better predict, manipulate and control the behaviors of pseudo-atoms, whether in batteries for solar farms or catalysts for bio-fuel production.
New information for textbooks starts with student project
This study began when Alexander Whiteside, a Heriot-Watt University student, came to PNNL as part of the 2008 Summer Research Institute for Interfacial and Condensed Phase Physics. During that summer visit, Whiteside, his advisor Maciej Gutowski, and Laboratory Fellow Sotiris Xantheas started to determine the electronegativity of the ammonium radical.
The team calculated the electronic structure of the neutral ammonium molecule, NH4, and its positive and negative ions. Next, they computed the properties of ammonium complexes, specifically combining ammonium with astatine or selected borohydrides; the latter are promising materials for hydrogen storage.
“These results clarified the properties of NH4 and placed it in the proper scale compared to the alkali metals,” said Xantheas. “Nobody had really put it into the scale yet. This study did just that.”
The results graced the cover of Chemistry: A European Journal and were highlighted in the Royal Society of Chemistry’s Chemistry World.
“Past generations of physical and theoretical chemists were intrigued by the properties of ammonium. Alex was standing on the shoulders of giants – Berzelius, Pauling, Mulliken, Herzberg – whose pictures are highlighted in the cover of the journal, while Sotiris and I helped him to keep his balance,” joked Gutowski.
Continuing to add to the scale
The team is expanding their work to the properties of the nearly ubiquitous hydronium and methyl groups, which contain a single oxygen or carbon atom and three hydrogen atoms. In addition, they are examining cyanide, a carbon and nitrogen atom combination that could provide new insights into that pseudo-atom’s behavior.
Submitted by DOE’s Pacific Northwest National Laboratory