188 The Poetry of Physics and The Physics of Poetry
completing a closed shell the six n = 6, l = 1 states. Period 7 begins to
repeat the pattern of period 6 but never completes it because there are not
enough elements. To date, 105 elements have been observed, 92 of
which occur in nature and 13 of which, the transuranic elements, have
been created artificially in the laboratory. The following states are
successively filled in period 7: the two n = 7, l = 0 states, the fourteen
n = 5, l = 3 states and finally, three of the n = 6, l = 2 states, which
accounts for the presently, observed elements.
The Bohr theory of the atom explained a great deal regarding the
spectrographic and chemical properties of the atom. It had serious
shortcomings, however. In spite of the correspondence principle it was
never really able to successfully calculate the probability for a particular
atomic transition and hence, could not account for the relative intensity
of spectral lines. There were also other aspects of the spectroscopic data
that could not be explained within the framework of Bohr’s model.
Although Bohr’s model was to be replaced with the more sophisticated
wave mechanics, many features of Bohr’s theory would be retained in
the new quantum theory. Bohr’s theory had been invaluable; for many
years it provided a framework for organizing the wealth of information
gathered by the spectroscopists.
Before passing on to wave mechanics I would like to share with the
readers my 15 minutes of fame when I had lunch with Niels Bohr in
- I was a first year student at MIT and Bohr was on campus to give
some lectures. I saw him enter the cafeteria by himself. I jumped up
from my table and ran to the cafeteria line and stood exactly behind
him. Timidly I said to him, “Good afternoon Prof. Bohr.” He wheeled
around and said to me, “How do you do? I am Niels Bohr.” I said hello
and said, “I am Bob Logan”. He asked me if I would like to join him for
lunch, which I did. I sat there for those 15 minutes conversing with the
great man himself. He was very kind and inspiring exactly as he was
known by his reputation. Every time I would teach the Bohr atom as a
professor in later years I would always tell this story to the delight and
inspiration of my students. In subsequent years I met his son Aage Bohr
at Los Alamos and only just recently in August of 2009 his grandson
Tomas Bohr in Copenhagen, all physicists and just as kind and inspiring
as their famous father and grandfather.