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Untangling the mystery of electrons

Walter Kohn John Pople

(CNN) -- For most of the 20th century, scientists have understood that electrons -- tiny charged particles floating about atoms, which are the building blocks of all matter -- played a pivotal role in how different chemical compounds reacted to each other.

The problem for chemists, however, was in trying to keep track of how all those electrons would behave in any given reaction. That was particularly true when looking at complex molecules, which are made up of many atoms and, thus, even more electrons.

The process has been described as trying to model the behavior of a room full of unruly schoolchildren. In 1929, the eminent Nobel laureate Paul Dirac deemed the mathematical equations involved so complex that, he said, no one would ever be able to figure them out.

But thanks to Walter Kohn and John Pople, chemists today routinely use computers to track electrons, speeding the development of new drug compounds and allowing astronomers to study the makeup of interstellar matter.

For their work, Kohn and Pople have been awarded the 1998 Nobel Prize in chemistry.

In the 1960s, Kohn, now a physics professor at the University of California at Santa Barbara, developed shortcuts to keeping track of electrons by figuring out a simplified method of averaging their movements. That made the calculations involved much less daunting than they seemed in Dirac's day.

Then in 1970, Pople, now a chemistry professor at Northwestern University in Evanston, Illinois, developed a program, called GAUSSIAN-70, that enabled chemists to harness the power of the computer to model chemical behavior. By the early 1990s, subsequent versions of GAUSSIAN had been refined to the point that it could be used by chemists to put Kohn's breakthrough into action.

Taken together, these two developments have enabled scientists to analyze the behavior of highly complex molecules without ever stepping into a laboratory and picking up a test tube.

For example, scientists who are looking into how pollutants released into the atmosphere might deplete the ozone layer can model and test the myriad complex chemical interactions involved, leading to a better understanding of the problem -- and ways to make the atmosphere cleaner.