1. Introduction

1.1 Chemistry at the Borders to Physics and Biology

The turn of the century 1900 was also a turning point in the history of chemistry. Consequently, a survey of the Nobel Prizes in Chemistry during this century will provide an analysis of important trends in the development of this branch of the Natural Sciences, and this is the aim of the present essay. Chemistry has a position in the center of the sciences, bordering onto physics, which provides its theoretical foundation, on one side, and onto biology on the other, living organisms being the most complex of all chemical systems. Thus, the fact that chemistry flourished during the beginning of the 20th century is intimately connected with fundamental developments in physics.

In 1897 Sir Joseph John Thomson of Cambridge announced his discovery of the electron, for which he was awarded the Nobel Prize for Physics in 1906. He found that these negatively charged 'corpuscles', as he called them, have a mass 1000 times smaller than the hydrogen atom. Thomson's discovery had, of course, important implications for chemistry, as it showed that the atom is not an indivisible building block of chemical compounds, but it took a number of years before this led to developments of direct relevance to chemistry. In 1911 Ernest Rutherford, who had worked in Thomson's laboratory in the 1890s, formulated an atomic model, according to which the positively charged atomic nucleus carries most of the mass of the atom but occupies a very small part of its volume.

This is instead created by a cloud of electrons circling around the nucleus. Rutherford received the Nobel Prize for Chemistry already in 1908 for his work on radioactivity (see Section 2).

It was soon realized that in Rutherford's atomic model the stability of atoms was at variance with the laws of classical physics, since the electrons would lose energy in the form of electromagnetic radiation and eventually fall into the nucleus. Niels Bohr from Copenhagen understood that an important clue to the solution of this problem could be found in the distinct lines observed in the spectra of atoms, the regularities of which had been discovered in 1890 by the physics professor Johannes (Janne) Rydberg at Lund University. Consequently, Bohr formulated in 1913 an alternative atomic model, in which only certain circular orbits of the electrons are allowed. In this model light is emitted (or absorbed), when an electron makes a transition from one orbit to another. Bohr received the Nobel Prize for Physics in 1922 for his work on the structure of atoms.

Another step in the application of the electronic structure of atoms to chemistry was taken in 1916, when Gilbert Newton Lewis suggested that strong (covalent) bonds between atoms involve a sharing of two electrons between these atoms (electron-pair bond). Lewis also contributed fundamental work in chemical thermodynamics, and his brilliant textbook, Thermodynamics (1923), written together with Merle Randall, is counted as one of the masterworks in the chemical literature. Much to the surprise of the chemical community, Lewis never received a Nobel Prize.

Even if the contributions just described were made a decade or more after Thomson's discovery, much important work in the borderland between physics and chemistry was published in the 1890s, and this was naturally given a strong consideration by the first Nobel Committee for Chemistry (see Section 2). In fact, three of the Laureates during the first decade, Jacobus Henricus van't Hoff, Svante Arrhenius and Wilhelm Ostwald, are generally regarded as the founders of a new branch of chemistry, physical chemistry. Fundamental work had, however, also been done in more traditional chemical fields, particularly in organic chemistry and in the chemistry of natural products, which is clearly reflected in the early prizes. The Nobel Committee, in addition, showed great openness and foresight by recognizing the other border, that towards biology, already in 1907 with the prize to Eduard Buchner "for his biochemical researches and his discovery of cell-free fermentation".

1.2 The Mechanics of the Work in the Nobel Committee for Chemistry
According to the statutes of the Nobel Foundation, the Nobel Committees should have five members, but the Committee for Chemistry has in recent decades chosen to widen its expertise by adding a number of adjunct members (five in 1998) with the same voting rights as the regular members. Until recently there was no limit other than age on how many times regular members could be re-elected for 3-year terms, so that some members sat on the Committee for a very long period. For example, Professor Arne Westgren of Stockholm, who was secretary of the Nobel Committees for Physics and for Chemistry 1926-1943, was also Chairman of the Committee for Chemistry 1944-1965. Present rules, however, only allow two re-elections, so that a member's maximum total time on the Committee will be nine years.

Only persons that have been properly nominated before 31 January can be considered for the Nobel Prize in a given year. Consequently, the Nobel Committee starts its work by sending out invitations to nominate in the autumn of the preceding year. Recipients of these invitations, for both Physics and Chemistry, are: 1) Swedish and foreign members of the Royal Swedish Academy of Sciences; 2) members of the Nobel Committees for Physics and for Chemistry; 3) Nobel Laureates in Physics and Chemistry; 4) professors in Physics and Chemistry in Scandinavian universities and at Karolinska Institutet; 5) professors in these subjects in a number of universities outside Scandinavia, selected on a rotation basis by the Academy of Sciences; and 6) other scientists that the Academy chooses to invite.

In the initial years of the Nobel Prize, about 300 invitations to nominate for the Nobel Prize for Chemistry were sent out, but this number has increased over the years and was as high as 2,650 in 1998. The number of nominations received has also increased dramatically from 20-40 during the first decade to 400-500 in the 1990s. The number of candidates is usually smaller than the number of nominations, since many candidates receive more than one nomination. During the first few years only about 10 scientists were nominated, but in recent years this number has been in the range of 250-350.

The invitations to nominate are personal, and it is stressed that nominations should not be discussed with the candidate or with colleagues. This is unfortunately not always respected as is obvious from the fact that many identically worded nominations are some years received from the same university. For this reason the Committee does not put much weight on the number of nominations a given candidate receives, unless clearly independent nominations come from different universities in different countries. This attitude was not taken in earlier years however, as is evident from the following statement made by Committee Chairman Arne Westgren, in a survey over the first 60 years of the Nobel Prize for Chemistry [1]: "In fact, if a scientist is proposed by a large number of sponsors in the preliminary international voting, he is normally selected by the Academy."
Often the same candidate receives nominations both for chemistry and for physics or for chemistry and for medicine. This problem was met already in 1903, when Arrhenius had been nominated both for the Prize for Chemistry and that for Physics, and in its deliberations the Committee for Chemistry suggested that he should be awarded half of each Prize, but this idea was rejected by the Committee for Physics. Because of such borderline problems, the Committee for Chemistry nowadays has joint meetings with those for Physics and for Physiology or Medicine. However, as pronounced by Westgren [1]: "It is now generally recognized that the important thing is to decide whether work which can with equal justice be reckoned as chemistry and physics or chemistry and medicine, is in fact worthy of a Nobel Prize." For example, Peter Mitchell, who received the 1978 Nobel Prize for Chemistry, could with equal justice have been awarded the Prize for Physiology or Medicine.

Nobel's will laid down that the prize should be awarded for work done during the preceding year, but in the statutes governing the committee work this has been interpreted to mean the most recent results, or for older work provided its significance has only recently been demonstrated. It was undoubtedly this rule that excluded Stanislao Cannizzaro from receiving one of the first Nobel Prizes, since his work on drawing up a reliable table of atomic weights, helping to establish the periodic system, was done in the middle of the 19th century. A more recent example is Henry Eyring, whose brilliant theory for the rates of chemical reactions, published in 1935, was apparently not understood by members of the Nobel Committee until much later. As a compensation the Royal Swedish Academy of Sciences gave him, in 1977, its highest honor, other than the Nobel Prize, the Berzelius Medal in gold.