Presentation Speech by Professor G. Hägg, member of the Nobel Committee for Chemistry of the Royal Swedish Academy of Sciences
Your Majesties, Your Royal Highnesses, Ladies and Gentlemen.
When, in the early nineteenth
century, Dalton had produced experimental proofs
that matter consists of atoms it was not long before an explanation was sought
of the forces that bind the atoms together. Berzelius was of the opinion that
this chemical bond was caused by electrostatic attraction between the atoms;
according to this belief, a bond was established between two atoms if one of
the atoms was positively, and the other negatively charged. In 1819 when Berzelius
presented his theory he could apply it almost exclusively to inorganic substances;
only few organic substances were known as pure compounds, and the study of these
was difficult due to their complicated and often insufficiently known composition.
Berzelius, however, contrived to explain, with the help of the new theory, the
bond conditions for a great number of inorganic substances, and could in this
wav contribute in a high degree to a greater clarity in this field.
Even in inorganic chemistry, however, certain difficulties arose. How should
one explain, for instance, how
two hydrogen atoms unite to become a hydrogen
molecule? In order to obtain attraction between atoms, one of the atoms must
be positive and the other negative; but why should two atoms of the same kind
possess charges with opposite sign? And when the knowledge of organic compounds
increased, new difficulties arose. Berzelius, for example, found it necessary
to assume that the hydrogen atom was always positive and the chlorine atom always
negative. Now it was also found that in organic molecules a hydrogen atom could
often be exchanged for a chlorine atom, which should be impossible if one was
positive and the other negative.
With increased knowledge, problems that could not be explained by Berzelius'
theory became more and more numerous, and the theory became discredited.
After the atomic theory had been accepted, it soon became apparent that another
important object in the field of chemistry must be to determine not only the
nature of the chemical bond but also how the atoms are arranged geometrically
when they unite to form larger groups, such as molecules. Permit me to quote
from a book, remarkable in its day, Die Chemie der Jetztzeit written
in 1869 by the Swedish chemist Blomstrand:
"It is the important task of the chemist to imitate faithfully in his own way
the elaborate constructions which we call chemical compounds, and in the erection
of which the atoms have served as building stones, to determine as to number
and relative position incest family Prize pictures Nobel Chemistry in the points of attack at which one or the other of the
atoms attaches itself to the other, in short, to determine the distribution
in space of the atoms."
Blomstrand makes it the aim, therefore, to find the geometrical construction
of substances, or what is nowadays called their structure.
At the end of the last century it became obvious that one had to consider several
different kinds of chemical bond. Thus, the difficulties of the Berzelius theory
were also explained. Berzelius' interpretation was in principle correct as regards
a very important type of bond, but he had made the mistake of applying it also
to bonds of a different type. After Bohr had introduced his atomic theory one
could moreover with its help give a fairly satisfactory explanation of the Berzelius
bond. As this bond occurs between electrically charged atoms, so-called ions,
this bond type has often been called the ionic bond. The most typical ionic
bonds unite the atoms in the crystals of simple salts.
The bond which above all others had prevented a general application of the Berzelius
theory is now commonly known as the covalent bond. It occurs commonly when atoms
unite to form a molecule and was once characterized by the famous American chemist
Gilbert Newton Lewis as "the chemical bond". The bond between the two
hydrogen atoms in a hydrogen molecule, which, as was said before, could not
be explained by Berzelius' theory, is covalent.
For a long time it was difficult to explain
the nature of the covalent bond.
Lewis, however, succeeded in 1916 in showing that it is brought about by electrons
- generally two - which are shared in common by two neighbouring atoms, thereby
uniting them. Eleven years later Heitler and London were able to give a quantum-mechanical
explanation of the phenomenon. An exact mathematical treatment of the covalent
bond, however, was possible only in the simple case where only one electron
unites the two atoms, and when these do not contain additional electrons outside
the atomic nuclei. Even for the hydrogen molecule, which contains two electrons,
the treatment cannot be absolutely exact, and in still more complicated cases
the mathematical difficulties increase rapidly. It has, therefore, been necessary
to use approximate methods, and the results depend to Prize sex girl Nobel in Chemistry snake a large extent Nobel Prize rape Chemistry stories in abduction free on Взрывозащищенный электродвигатель Nobel Prize Chemistry ВАО in the
in Prize Nobel Chemistry celebrity upskirt choice of Prize girl sex Chemistry Nobel in snake suitable methods and the manner of their application.
Linus Pauling has actively contributed towards the development of these methods,
and he has applied them with extreme skill. The results have been such as to
be easily usable by chemists. Pauling has also eagerly sought to apply his views
to a number of structures which have been experimentally determined during the
last decades, both in his own laboratory in Pasadena and elsewhere. It is hardly
necessary to mention that we have nowadays great possibilities of reaching Blomstrand's
objective of determining the distribution of atoms in space. This is principally
done by methods of X-ray crystallography involving an examination of how a crystal
influences X-rays in certain respects, and then out of the effect seeking to
determine how the atoms are placed in the crystal. Pauling's methods have been
very successful and have led to observations which have further advanced the
theoretical treatment.
But if the structure of a substance is too complicated it may become impossible
to make a more direct determination of the structure with X-rays. In such cases
it may be possible, from a knowledge of bond types, atomic distances and bond
directions, to predict the structure and then examine whether the prediction
is supported by the experiments. Pauling has tried this method in his studies
of the structure of proteins with which he has been occupied during recent years.
To make a direct determination of the structure of a protein by X-ray methods
is out of the question for the present, owing to the enormous number of atoms
in the molecule. A molecule of the coloured blood constituent hemoglobin, which
is a protein, contains for example more than 8,000 atoms.
In the late nineteen thirties Pauling and his colleagues had already begun to
determine with X-rays the structure of amino acids and dipeptides, that is to
say, compounds of relatively simple structure containing what may be called
fragments of proteins. From this were obtained valuable information - about
atomic distances and bond directions. These values were supplemented by the
determination of the probable limits
of variation for distances and directions.
On this basis Pauling deduced some possible structures of the fundamental units
in proteins, and the problem was then to examine whether these could explain
the X-ray data obtained. It has thus become apparent that one of these structures,
the so-called alpha-helix, probably exists in several proteins.
How far Pauling is right in detail still remains to be proved, but he has surely
found an important principle in the structure of proteins. His method is sure
to prove most productive in continued studies.
It is hardly necessary to question the practical use of the knowledge of the
nature of chemical bonds and of the structure of substances. It is obvious that
the properties of a substance must largely depend on the strength with which
its atoms are united and the nature of the resulting structure. This I does
not only apply to the physical properties of the substance, for instance hardness
and melting point, but also to its chemical properties, that is to say how it
participates in chemical reactions. If we know how certain atoms or groups of
atoms are placed in a molecule we can often predict how the molecule should
react under given conditions. And as every reaction results in the breaking
of some bonds and the formation of others the result will largely depend on
the relative strength of the different bonds.
 
Professor Pauling. Since you began your scientific career
more than thirty years ago
you have covered a diversity of subjects ranging
over wide fields of chemistry, physics, and even medicine. It has been said
of you that you have chosen to live "on the frontiers of science" and we chemists
are keenly aware of the influence and the stimulative effect of your pioneer
work.
Wide though your field of activity may be, you have devoted the greater part
of your energy to the study of the nature of the chemical bond and the determination
of the structure of molecules and crystals.
It is with great satisfaction, therefore, that the Royal Swedish Academy of
Sciences has decided to award to you this year's Nobel Prize for Chemistry for
your brilliant achievements in this fundamental field of chemistry.
On behalf of the Academy I wish to extend to you our heartiest congratulations,
and now ask you to receive from the hands of His Majesty the King, the Nobel
Prize for Chemistry for the year 1954.
From Nobel Lectures, Chemistry 1942-1962, Elsevier Publishing Company, Amsterdam, 1964
 
|