World of Scientific Discovery on Svante August Arrhenius
Arrhenius had been an excellent scholar from a very early age. He taught himself to read when he was three, and he was the youngest student in his high school graduating class. Arrhenius's ancestors had traditionally been farmers, but his father, a surveyor and administrator on a Swedish estate, moved the family to the city of Uppsala in the early 1860s to take a position as a supervisor at the University of Uppsala.
Arrhenius entered the University of Uppsala at age seventeen where he studied mathematics, chemistry, and physics and earned his bachelor 's degree in 1878. After three years of graduate study, he became disenchanted with the university because its physics department concentrated on the study of light, a subject in which Arrhenius had little interest. In 1881, he transferred to the Swedish Academy of Sciences, where he studied electrical theory under Erik Edlund (1819-1888). After three years of research, Arrhenius returned to Uppsala to present his doctoral dissertation and win his degree.
At that time, scientists had known for a century that some substances would conduct electricity when dissolved in water but not in their dry state. These compounds were called electrolytes. Substances that would not conduct electricity when dissolved were called non-electrolytes. In the early 1800s, Humphry Davy had shown that molecules could be broken down into their elements through electrolysis. This process involved dissolving a substance and then passing an electric current through the solution. Michael Faraday had used the word ion to refer, hypothetically, to particles of electricity, just as particles of matter were called atoms. But no one had explained what an ion was or why some solutions would conduct electric current and others would not.
Arrhenius decided that the key to this mystery lay in the nature of the dissolved substance itself. He performed hundreds of experiments, measuring the conductivity of various compounds in solution, studying how the solutions' properties varied with the amount of compound dissolved, and measuring the boiling points and freezing points of the solutions. Arrhenius knew that water would freeze at lower temperatures when a non-electrolyte, such as sugar, was dissolved in it. If the quantity of sugar was doubled, the freezing point would be lowered twice as much--the more particles in a solution, the lower the freezing point. But for an electrolyte, such as salt (sodium chloride), the freezing point was twice as low as it should be--meaning that for a given number of molecules, twice as many particles were present in the solution. This suggested to Arrhenius that each molecule of sodium chloride produced two particles. For larger, more complex compounds, such as barium chloride and sodium sulfate, each molecule lowered the solution's freezing point three times as much, meaning that three particles had been created.
To explain this behavior, Arrhenius came up with a simple but revolutionary answer. He proposed that when a molecule of an electrolyte dissolves in a solution, it separates into charged particles called ions and that the electrical charges that the ions carry enable the solution to conduct electricity. Salt, for example, separates into two ions--a positively charged sodium ion and a negatively charged chlorine ion. During electrolysis, ions migrate through the solution, the negative ones being attracted to the positive electrode and vice versa. Arrhenius proposed that when an ion reaches an electrode, its charge is neutralized and uncharged atoms of the element are produced.
Arrhenius's theory was rejected, not only by his professors but also by the scientific establishment. The idea of an atom being electrically charged was inconceivable to chemists of the day, who believed that atoms were solid particles that could not be divided or changed. But luckily for Arrhenius, a few scientists had enough imagination to be intrigued by his theory. Arrhenius had sent copies of his thesis to several prominent chemists, including Friedrich Wilhelm Ostwald, who visited Arrhenius in Sweden. Despite Arrhenius's low grade on his thesis, he was given a teaching position and a travel grant, thanks to the influence of his supporters.
For the next several years, Arrhenius continued to develop his theory while Ostwald and others helped publicize it. Although Arrhenius's ideas were gradually being accepted, validation of his theories resulted from discoveries made by other scientists. In the 1890s, Joseph J. Thomson identified the electron, a subatomic particle that carries a negative charge, and Henri Becquerel discovered radioactivity, showing that atoms could break apart and emit particles such as electrons.
Finally, Arrhenius's theory made sense to everyone. In solid form, salt molecules were held together by the electrical attraction between sodium and chlorine atoms. When insulated by water, the atoms came apart (or "dissociated"), creating charged ions that had gained or lost electrons. The behavior of these dissociated ions is very different from that of atomic sodium, which is a metal, and atomic chlorine, a poisonous green gas. In 1903, Arrhenius was awarded the Nobel Prize in chemistry for the same theory that his professors had scorned less than twenty years earlier.
In addition to his theory of electrolytic dissociation, as it came to be called, Arrhenius discovered a concept that has become essential to the modern theory of catalysis. During his research on solutions, Arrhenius became interested in the influence of temperature on the speed of chemical reactions. In 1889, he discovered that reactions would take place much faster when heat was supplied. Arrhenius suggested that molecules had to be "activated," or energized, in order to take part in a reaction. The speed of the reaction depends on the number of activated molecules present and is related to the "energy of activation"-- the quantity of energy that must be added to the molecules to trigger a reaction. Arrhenius developed an equation for this relationship that explains chemical reaction rates.
Arrhenius's rise in the scientific community coincided with the birth of a new discipline called physical chemistry. Until then, chemistry and physics had been strictly divided. That was one of the original problems with Arrhenius's ideas--they just did not fit into one exclusive category. But Arrhenius, along with Ostwald and other chemists in the vanguard, established the connection between physics and chemistry, creating a new interdisciplinary science.
During the late 1880s, Arrhenius had worked throughout Europe in some of the most modern laboratories of the day, and he had been offered jobs at many prestigious foreign universities. But Arrhenius always preferred, for patriotic reasons, to teach in Sweden. He lectured at the University of Uppsala and Stockholm's Högskola before being appointed director of physical chemistry at the newly created Nobel Institute in Stockholm, a position he retained for the remainder of his life.
Once he won the scientific community's respect, Arrhenius felt free to contemplate the deeper mysteries of the universe. Some of his later ideas were questionable. For instance, he believed that life on Earth had sprung from "spores" that had been driven through outer space by radiation pressure from other planets. Nevertheless, Arrhenius's clear writing helped popularize science, and his books and articles, translated into several languages, were immediately successful worldwide.
At least one of his later theories is now widely accepted. Arrhenius speculated that carbon dioxide gas in the atmosphere traps heat by allowing sunlight to reach earth but blocking the radiation of heat away from the planet. Today, this phenomenon is called the greenhouse effect. Many scientists think that global warming can be caused by the carbon dioxide that is released when fossil fuels, such as coal, are burned in factories and power plants. Arrhenius suggested that carbon dioxide may have caused great climatic changes in the past, such as the Ice Age and the warm era when the dinosaurs lived.
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