Chemistry Reference
In-Depth Information
sublimed. Of special importance was the accuracy of the atomic weights of key
elements silver, chlorine, bromine, sodium, potassium and sulphur. The rela-
tive precision for the atomic weight of silver (107.880) was 1:100 000 which was
and is considered to be high-performance analytical chemistry. Particular impor-
tance was given to the atomic weight determination with the study of radioactiv-
ity and for the evidence of existing isotopes. Hönigschmid was able to determine
the atomic weights of
35
Cl and
37
Cl after their separation by Clusius and Dickel
in 1938 [
25
]. With the new technique of mass spectroscopy by Aston, there was
a fruitful exchange of information and complementary support. For many years,
Hönigschmid was the head of the German Atomic Weights Commission and
from 1930 also active in the corresponding international committee of IUPAC.
Hönigschmid was member of several academies. He received the
Goethe
-
Medaille
für Kunst und Wissenschaft
(Goethe Medal for Arts and Science) [
26
] and 1940 the
Liebig
-
Medaille
of the German Chemical Society.
Otto H
ahn
(born 8 March 1879, Frankfurt, Main, died 28 July 1968, Göttingen)
Otto Hahn was the son of an innovative factory owner [
27
]. After high school
in Frankfurt, Main, he intended to become an industrial chemist and matriculated
1897 in Marburg. Before completion of his PhD in Marburg in 1901, he spent two
semesters with Adolf von Baeyer in München. After 1 year military service, he
worked for 2 years as assistant at the Universität Marburg. In 1904, Hahn moved
to the University College London and had his first experience in radiochemis-
try with Sir William Ramsay. In 1905, he discovered radiothorium, then consid-
ered a new chemical element, now known as
228
Th. Later that year, Hahn went
to Sir Ernest Rutherford at McGill University, Montreal, Canada. There he dis-
covered the radioactive elements thorium C (now
222
Bi), radium D (now
220
Pb),
and radioactinium (now
227
Th) [
28
]. In 1906, Hahn returned to Germany to work
with Emil Fischer, Friedrich-Wilhelms-Universität (now Humboldt-Universität)
Berlin, and discovered within a few months mesothorium I, mesothorium II and
the mother substance of radium-ionium. Mesothorium I (now
228
Ra) had a high
potential for medical radiation therapy [
29
]. For the discovery of mesothorium I,
Hahn was for the first time proposed for the Nobel Prize in Chemistry (in 1914 by
Adolf von Baeyer). In 1907, Hahn qualified as university lecturer (habilitation the-
sis) at the Friedrich-Wilhelms-Universität Berlin.
In 1907, Lise Meitner came to Berlin from Vienna. They cooperated for more
than 30 years and established a lifelong close friendship (see Fig.
4.5
). In 1908,
Hahn succeeded in demonstrating the radioactive recoil incident to alpha parti-
cle emission and thus interpreting it correctly [
30
]. In 1910, Hahn was appointed
Professor, and in 1912, he became Head of the Radiochemistry Department of the
newly founded Kaiser-Wilhelm-Institut für Chemie in Berlin [
31
].
During the First World War, Hahn was conscripted into the army, where he was
assigned, together with James Franck and Gustav Hertz, to the special unit for
chemical warfare under the direction of Fritz Haber. Hahn resumed his research
with Lise Meitner in 1918 and discovered protactinium, the long-lived mother sub-
stance of the actinium series. Hahn published the first report on his discovery of
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