Once physicists studying the structure of the atom began to realize
that the electrons surrounding the nucleus had a special arrangement,
chemists began to investigate how these theories corresponded to the known
chemistry of the elements and their bonding abilities. Two Americans who
were instrumental in developing a bonding theory based on the number of
electrons in the outermost "valence" shell of the atom were Gilbert Newton
Lewis (1875–1946) and Irving Langmuir (1881–1957).
In 1902, while
Lewis was trying to explain valence to his students, he depicted atoms as
constructed of a concentric series of cubes with electrons at each corner.
This "cubic atom" explained the eight groups in the periodic table and
represented his theory that chemical bonds are formed by electron
transference to give each atom a complete set of eight. In 1923 he redefined
acids as any atom or molecule with an incomplete "octet" that were thus
capable of accepting electrons from another atom; bases were, of course,
electron donors.
Lewis was also important in developing the field of thermodynamics and
applying its laws to real chemical systems. At the end of the nineteenth
century when he started working, the law of conservation of energy and other
thermodynamic relations were known only as isolated equations. Lewis built
on the work of another American pioneer in thermodynamics, Josiah Willard
Gibbs (1839–1903) of Yale University, whose contributions were only slowly
recognized. Their work was of immense value in predicting whether reactions
will go almost to completion, reach an equilibrium, or proceed almost not at
all, and whether a mixture of chemicals can be separated by distillation.
Lewis was educated at home, while his family
lived in Massachusetts and Nebraska, until he was fourteen years old. His
subsequent education was more conventional, although nonetheless
stimulating, and included a Ph.D. from Harvard University earned under Theodore
W. Richards. Lewis then made the pilgrimage to Germany to work with the
physical chemists Walther Nernst and Wilhelm Ostwald. He held several
university faculty appointments, including ones at the Massachusetts
Institute of Technology and the University of California at Berkeley, where
he expanded the programs in chemistry and chemical engineering.
As a research pioneer for the General
Electric Company, Irving Langmuir made scientific contributions in
chemistry, physics, and atmospheric science. He received his doctorate from
Walther Nernst in Göttingen, Germany, but became bored after one year of
teaching college. In 1909 he arrived at the recently established GE Research
Laboratory. His first job was to solve the problems they were having with
the new tungsten filament light bulbs. Langmuir concentrated on the basic
principles on which the lamp operated, investigating the chemical reactions
catalyzed by the hot tungsten filament. He suggested filling the bulbs with
nitrogen gas (and later argon gas) and twisting the filament into a spiral
form to inhibit the vaporization of tungsten.
His
interest in fundamentals involved him in the theory of chemical bonding in
terms of electrons, and he elaborated on ideas first expressed by Gilbert
Lewis. Langmuir proposed that octets could be filled by sharing pairs
between two atoms—the "covalent" bond. His studies of surface chemistry—the
study of chemical forces at the contact surfaces (interfaces) between
different substances, where so many biologically and technologically
important reactions occur—earned him the Nobel
Prize in chemistry in 1932. Langmuir developed a new concept of adsorption,
according to which every molecule striking a surface remains in contact with
it before evaporating, thus forming a firmly held monolayer—in contrast to
earlier theories that likened adsorption to the attraction of the earth for
the gases in the atmosphere, where the attraction diminishes as distance
from the earth increases. He developed a multitude of experimental
techniques, including the extensive use of vacuum tubes to study solid–gas
interfaces and of oil films to study liquid–liquid interfaces. Other
practical work with theoretical implications—on electrical discharges in
gases—helped to lay the foundation for "plasma" physics, which has
application today in attempts at controlled nuclear fusion. He maintained a
lifelong interest in meteorology, including work developing aircraft
de-icing capabilities during World War II. Here too he pushed beyond
observation to theory, which led to his carrying out early experiments in
"seeding" clouds with solid carbon dioxide particles to produce rain.
