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Arrhenius, Svante August (1859-1927) was a Swedish physical chemist who first explained that in an electrolyte (a solution of a chemical dissolved in water) the dissolved substance is dissociated into electrically charged ions. The electrolyte conducts electricity because the ions migrate through the solution. Although later modified, Arrhenius' theory of conductivity in solutions has stood the test of time. It was a major contribution to physical chemistry, ultimately acknowledged by the award to Arrhenius of the 1903 Nobel Prize in Chemistry. Arrhenius was born in Uppsala on 19 February 1859, the son of a surveyor and estate manager who was also a supervisor at the local university. He was a brilliant student, entering Uppsala University at the age of 17 to study chemistry, physics and mathematics. After graduating in 1878, he stayed to write his doctoral thesis, but became dissatisfied with the teaching at Uppsala and went to Stockholm to study solutions and electrolytes under Erik Edlund (1819-1888). In 1884 he submitted his thesis, which contained the basis of the dissociation theory of electrolytes (although he did not at that time use the term dissociation), together with many other novel theories which aroused only suspicion and doubt in his superiors. The largely theoretical document was not welcomed by the academics, who were devoted experimentalists; Arrhenius later boasted that he had never performed an exact experiment in his life and preferred to take a general view of relationships from the results of many approximate experiments. The thesis (written in French) was awarded only a fourth class, the lowest possible pass, but Arrhenius sent copies of it to several eminent chemists, including Friedrich Wilhelm Ostwald (at Riga), Rudolf Clausius (Bonn), Lothar Meyer (Tübingen) and Jacobus Van't Hoff (Amsterdam). Ostwald's offer to Arrhenius of an academic appointment moderated the scepticism of the Uppsala authorities, who finally offered him a position and, later, a travelling fellowship. This enabled him to spend some time with other scientists working in the same field, such as Friedrich Kohlrausch and Hermann Nernstat Würzburg, Ludwig Boltzmann at Graz and Jacobus van't Hoff, whose solution theories paralleled that of Arrhenius. In 1891 Arrhenius was offered a professorship at Giessen in Germany as successor to Justus von Liebig, but he declined in preference for an appointment at the Royal Institute of Technology in Stockholm. Four years later he became professor of physics at a time when his work was attracting the attention of scientists throughout Europe, if not in his native Sweden- his election to the Swedish Academy of Sciences had to wait another six years until 1901 (the same year in which Van't Hoff was awarded the first Nobel Prize in Chemistry). He again declined a German professorship, in Berlin, in 1905 and took instead the specially created post of Director of the Nobel Institute of Physical Chemistry (Stockholm), where he remained until shortly before his death on 2 October 1927. The Arrhenius theory of electrolytes (1887) is concerned with the formation, number and speed of ions in solution. The key to the theory is the behaviour of the dissolved substance (solute) and the liquid (solvent), both of which are capable of dissociating into ions. It postulates that there is an equilibrium between undissociated solute molecules and its ions, whose movement or migration can conduct an electric current through the solution. Its chief points may be summarized as follows: (a) An electrolytic solution contains free ions (i.e., dissociation takes place even if no current is passed through the solution). (b) Conduction of an electric current through such a solution depends on the number and speed of migration of the ions present. (c) In a weak electrolyte, the degree of ionization (dissociation) increases with increasing dilution. (d) In a weak electrolyte at infinite dilution, ionization is complete. (e) In a strong electrolyte, ionization is always incomplete because the ions impede each other's migration; this interference is less in dilute solutions of strong electrolytes. Apart from (e), regarding strong electrolytes (a difficulty not resolved until the work of Peter Debye and Erich Hückel in the 1920s), Arrhenius' theory is still largely accepted. In another notable achievement, Arrhenius adapted Van't Hoff's work on the colligative properties of non-electrolyte solutions. He found that solutions of salts, acids and bases - electrolytes - possess greater osmotic pressures, higher vapour pressures and lower freezing points than Van't Hoff's calculated values but explained the discrepancies in terms of ionic dissociation by taking into account the number of solute ions (as opposed to molecules) present. In 1889 Arrhenius suggested that a molecule will take part in a chemical reaction on collision only if it has a higher than average energy - that is, if it is activated. As a result, the rate of a chemical reaction is proportional to the number of activated molecules (not to the total number of molecules, or concentration) and can be related to the activation energy. After 1905 Arrhenius widened his research activities. For example, he applied the laws of theoretical chemistry to physiological problems (particularly immunology); once again initial criticism was replaced by universal acceptance. With N. Ekholm he published papers on cosmic physics concerning the Northern Lights, the transport of living matter ('spores') through space from one planet to another, and the climatic changes of the Earth over geological time - pointing out the 'greenhouse effect' brought about by carbon dioxide in the atmosphere. Arrhenius became more and more respected by the world of science and was much sought after for meetings, lectures and discussions throughout the world. In his latter years he had to rise at 4 am in order to maintain his scientific activities, and this consistent hard work probably contributed to his death at the age of 68. Author not available, Arrhenius, Svante August (1859-1927). , The Hutchinson Dictionary of Scientific Biography, 01-01-1998. |
