UNIVERSITY OF CALIFORNIA
DEPARTMENT OF CHEMISTRY
May 1, 1928
Professor Linus Pauling,
California Institute of Technology,
My dear Pauling:
I am getting to be an abominable correspondent, but I hope this will not discourage you from writing to me from time
to time, as you have done, and telling me of the things you are doing. When I received your recent letter I meant to reply
in some detail regarding the paper which you were good enough to enclose and which I have just seen in the Proceedings. I
have been wanting to think about these things myself, but just at present I have been entirely submerged in problems of quantum
statistics with Dr. Mayer. Whether we shall get anywhere is a problem.
I was, however, very much interested in your paper as I had been in London's, and there is much in both papers with
which I an agree. The success of Pauli's principle in the interpretation of complex spectra seemed to leave the physicists
no excuse for not accepting in its entirety the theory of paired electrons, coupled, whether or not they constitute a bond,
by the mutual neutralization of their magnatio moments; and it will be interesting to see whether it is going to be possible
to obtain any facts from the Pauli principle or from the new mechanics regarding chemical compounds which are not known to
or not yet interpreted by chemists. Of course the fundamental problem after the pairing of electrons is accepted is this:
why can we have only one pair in the K shell and only four pairs in the L shell, etc.?
I am sorry that in one regard my idea of valence has never been fully accepted. It was an essential part of my original
theory that the two electrons in a bond completely lost their identity and can not be traced back to the particular atom or
atoms from which they have come; furthermore that this pair of electrons is the only thing which we are justified in calling
a bond. Failure to recognize this principle is responsible for much of the confusion now prevailing in England on this subject,
where they still talk of polar bonds and semi-polar bonds, and so on. I think in London's paper and in yours a little too
much emphasis is placed upon the origin of the paired electrons.
I am sure that you and London are wrong in thinking that hydrogen does not have two bonds, but this is because
neither of you has considered the possibility that in a highly polar molecule the bond attaching hydrogen may not be in the
K level of the hydrogen but in the Level. This question is discussed briefly in my book on "Valence."
I am going abroad for a short time this summer, but shall not leave Berkeley until the middle of June. I hope you will not
be coming through Berkeley before then ad Ithat I will have a chance to talk with you.
With kindest regards, I am,
Yours very sincerely