INTRODUCTION
HENRY
GWYN JEFFREYS MOSELEY
Born : 23
November 1887, Weymouth, Dorset, United Kingdom
Died : 10 August 1915 (aged 27), Gallipoli,
Ottoman Empire
Education : Trinity
College, University of Oxford, University of
Manchester
1906 : Moseley
entered the Trinity College of the University of
Oxford, where he earned his
Bachelor’s degree.
1910 : Immediately
after graduation from Oxford in 1910, Mosely
became a demonstrator in Physics at
the University of
Manchester under the supervision of
Sir. Earnest Rutherford
1912 : Experimenting
with the energy of beta-particles in 1912.
Moseley showed that high potentials
were attainable from a
radioactive source of radium,
thereby inventing the first atomic
battery, though he was unable to produce the 1 Mev
ne
1913 : In
1913, Moseley observed and measured the X-ray spectra of
various chemical elements (Moseley
metals) that were formed
by method of diffraction through
crystals.
1914 : In
1914, Max Von law of Germany won the Nobel Prize for
Physics for his discovery of the diffraction of X-ray
by crystals, which was a crucial step towards the invention of X-ray
spectroscopy.
1915 : Moseley
was assigned to the force of British empire soldiers
that invaded the region of Gallipoli, Turkey, in
April 1915, as a telecommunication officer.
1915 : Moseley
was shot and killed during the battle of Gallipoli on
10th August 1915, at the
age of 27.
HENRY MOSELEY
Henry Gwyn Jeffreys Moseley known
as Harry Moseley (23 November 1887 – 10 August 1915) was an English physicist.
Moseley's contribution to the science of physics was the justification from
physical laws of the previous empirical and chemical concept of the atomic
number. This stemmed from his development of Moseley's law in X-ray spectra.
Moseley's Law justified many concepts in chemistry by sorting the chemical
elements of the periodic table of the elements in a logical order based on
their physics.
Moseley's law advanced atomic
physics by providing the first experimental evidence in favour of Niels Bohr's
theory, aside from the hydrogen atom spectrum which the Bohr theory was
designed to reproduce. That theory refined Ernest Rutherford's and Antonius van
den Broek's model, which proposed that the atom contains in its nucleus a
number of positive nuclear charges that is equal to its (atomic) number in the
periodic table. This remains the accepted model today.
When World War I broke out in
Western Europe, Moseley left his research work at the University of Oxford
behind to volunteer for the Royal Engineers of the British Army. Moseley was
assigned to the force of British Empire soldiers that invaded the region of
Gallipoli, Turkey, in April 1915, as a telecommunications officer. Moseley was
shot and killed during the Battle of Gallipoli on 10 August 1915, at the age of
27. Experts have speculated that Moseley could have been awarded the Nobel
Prize in Physics in 1916, had he not been killed. As a consequence, the British government
instituted new policies for eligibility for combat duty.
CONTRIBUTION
TO PHYSICS AND CHEMISTRY
Experimenting with the energy of
β-particles in 1912, Moseley showed that high potentials were attainable from a
radioactive source of radium, thereby inventing the first atomic battery,
though he was unable to produce the 1MeV necessary to stop the particles.
In 1913, Moseley observed and
measured the X-ray spectra of various chemical elements (mostly metals) that
were found by the method of diffraction through crystals. This was a pioneering
use of the method of X-ray spectroscopy in physics, using Bragg's diffraction
law to determine the X-ray wavelengths. Moseley discovered a systematic
mathematical relationship between the wavelengths of the X-rays produced and
the atomic numbers of the metals that were used as the targets in X-ray tubes.
This has become known as Moseley's law.
Before Moseley's discovery, the
atomic numbers (or elemental number) of an element had been thought of as a
semi-arbitrary sequential number, based on the sequence of atomic masses, but
modified somewhat where chemists found this modification to be desirable, such
as by the Russian chemist, Dmitri Ivanovich Mendeleev. In his invention of the
Periodic Table of the Elements, Mendeleev had interchanged the orders of a few
pairs of elements in order to put them in more appropriate places in this table
of the elements. For example, the metals cobalt and nickel had been assigned
the atomic numbers 27 and 28, respectively, based on their known chemical and
physical properties, even though they have nearly the same atomic masses. In
fact, the atomic mass of cobalt is slightly larger than that of nickel, which
would have placed them in backwards order if they had been placed in the Periodic
Table blindly according to atomic mass. Moseley's experiments in X-ray
spectroscopy showed directly from their physics that cobalt and nickel have the
different atomic numbers, 27 and 28, and that they are placed in the Periodic
Table correctly by Moseley's objective measurements of their atomic numbers.
Hence, Moseley's discovery demonstrated that the atomic numbers of elements are
not just rather arbitrary numbers based on chemistry and the intuition of
chemists, but rather, they have a firm experimental basis from the physics of
their X-ray spectra.
In addition, Moseley showed that
there were gaps in the atomic number sequence at numbers 43, 61, 72, and 75.
These spaces are now known, respectively, to be the places of the radioactive
synthetic elements technetium and promethium, and also the last two quite rare
naturally occurring stable elements hafnium (discovered 1923) and rhenium
(discovered 1925). Nothing about these four elements was known of in Moseley's
lifetime, not even their very existence. Based on the intuition of a very
experienced chemist, Dmitri Mendeleev had predicted the existence of a missing
element in the Periodic Table, which was later found to be filled by
technetium, and Bohuslav Brauner had predicted the existence of another missing
element in this Table, which was later found to be filled by promethium. Henry
Moseley's experiments confirmed these predictions, by showing exactly what the
missing atomic numbers were, 43 and 61. In addition, Moseley predicted the two
more undiscovered elements, those with the atomic numbers 72 and 75, and gave
very strong evidence that there were no other gaps in the Periodic Table
between the elements aluminium (atomic number 13) and gold (atomic number 79).
This latter question about the
possibility of more undiscovered ("missing") elements had been a
standing problem among the chemists of the world, particularly given the
existence of the large family of the lanthanide series of rare earth elements.
Moseley was able to demonstrate that these lanthanide elements, i.e. lanthanum
through lutetium, must have exactly 15 members – no more and no less. The
number of elements in the lanthanides had been a question that was very far
from being settled by the chemists of the early 20th Century. They could not yet
produce pure samples of all the rare-earth elements, even in the form of their
salts, and in some cases they were unable to distinguish between mixtures of
two very similar (adjacent) rare-earth elements from the nearby pure metals in
the Periodic Table. For example, there was a so-called "element" that
was even given the chemical name of "didymium". "Didymium"
was found some years later to be simply a mixture of two genuine rare-earth
elements, and these were given the names neodymium and praseodymium, meaning
"new twin" and "green twin". Also, the method of separating
the rare-earth elements by the method of ion exchange had not been invented yet
in Moseley's time.
Moseley's method in early X-ray
spectroscopy was able to sort out the above chemical problems promptly, some of
which had occupied chemists for a number of years. Moseley also predicted the
existence of element 61, a lanthanide whose existence was previously
unsuspected. Quite a few years later, this element 61 was created artificially
in nuclear reactors and was named promethium.
HONOURS
Isaac Asimov speculated that, in
the event that he had not been killed while in the service of the British
Empire, Moseley might very well have been awarded the 1916 Nobel Prize in
Physics, which, along with the prize for chemistry, was not awarded to anyone
that year. Additional credence is given to this idea by noting the recipients
of the Nobel Prize in Physics in the two preceding years, 1914 and 1915, and in
the following year, 1917. In 1914, Max von Laue of Germany won the Nobel Prize
in Physics for his discovery of the diffraction of X-rays by crystals, which
was a crucial step towards the invention of X-ray spectroscopy. Then, in 1915,
William Henry Bragg and William Lawrence Bragg, a British father-son pair,
shared this Nobel Prize for their discoveries in the reverse problem —
determining the structure of crystals using X-rays
Memorial plaques to Moseley were
installed at Manchester and Eton, and a Royal Society scholarship, established
by his will, had as its second recipient the physicist P. M. S. Blackett, who
later became president of the Society.
CONCLUSION
Henry Gwyn Jeffreys Moseley known
as Harry Moseley (23 November 1887 – 10 August 1915) was an English physicist.
Moseley's contribution to the science of physics was the justification from
physical laws of the previous empirical and chemical concept of the atomic
number. This stemmed from his development of Moseley's law in X-ray spectra.
Moseley's Law justified many concepts in chemistry by sorting the chemical
elements of the periodic table of the elements in a logical order based on
their physics.
REFERENCE
www.wikipedia.org
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