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We began our consideration of atoms in the previous unit by citing the conclusions of John Dalton published in 1810. After a detailed study of the chemistry of the era, Dalton concluded that atoms were indivisible and unchanging. He had no evidence that would convince him otherwise. We need to remember that our own modern science, of which we are very proud, must be tested constantly to ensure that it is valid.

By the end of the nineteenth century, evidence that would alter the Dalton view of atomic structure began to appear. J.J. Thompson reported in 1897 that cathode rays behaved as though they were negatively charged particles and that they were present in all metals used as cathodes. He measured the charge-to-mass ratio of these particles (he could not measure the charge or the mass independently of the other)and cautiously speculated that they be smaller than hydrogen means that atoms have constituent parts. In turn, this speculation of constituent parts raised the question: if atoms contain negative particles while possessing an overall neutral charge, then how is the positive charge deployed?

Cut to the chase: in 1910, Rutherford put most of the atomic mass in a tiny kernel at the heart of the atom and Bohr made it work, to a rather good approximation by 1913. Thus a second brand of atomic physics is spawned; A) the behavior of the electrons is studied mostly by chemists who are interested in bonding and spectroscopy issues; B) the nature of the forces that hold the nucleus together are a focal point for physics types.

Many of these pioneers of atomic physics are seen in a formal photograph taken at the fourth Solvay conference in Belgium in 1927. (See the top of this page.) A poster memorializing this event was made available to high schools by a supplier of science equipment who entitled the portrait "The Architects of Modern Physics". The picture seems incongruous with the term "modern". In the context of this picture, "modern physics" refers to those findngs revolving around the quantum. It should be noted that, as it was the custom of the time, all participants, save Marie Curie, are male. The participants are all gray; if this were a color picture, they would still be gray. Position in the photo is important; gods are placed in the front row, center. Others are relegated to other rows or to the sides.

A. Becquerel discovers Radioactivity

B. Radiation detectors

C. Artificial transmutation of the elements

D. Particle Accelerators

E. Nuclear fission

F. Nuclear fusion

.G. Quarks

H.Biological effects of nuclear radiation


Click on MODERN PHYSICS PEOPLE 2 to find a list of people who have made a significant contribution to our understanding of the atom and its outer structure. On the instructor's door is a sign-up sheet. Select one of the persons listed and prepare a biographical profile of your physicist. Along the way, in addition to relating what he/she did for science, describe any pertinent details about his/her private, non-science life that may give you a sense of the people-issues surrounding their work. This paper should be a minimum two pages in length and should be written according to the style approved by the English department.

References - For useful references regarding this topic, go to REFERENCES.

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last edited 12/29/05