Henry Moseley

Henry Moseley

Infobox Scientist
name = Henry Moseley
box_width = 300px

image_size = 300px
caption = Henry Moseley at work. This rare image is the only non-portrait photograph known of the physicist.
birth_date = November 23, 1887
birth_place = Weymouth, Dorset
death_date = August 10, 1915
death_place = Gallipoli, Turkey
residence = |citizenship =
nationality = English
ethnicity =
field = Physicist
work_institutions =
alma_mater =
doctoral_advisor =
doctoral_students =
known_for = Atomic number, Moseley's law
author_abbrev_bot =|author_abbrev_zoo =
influences =
influenced =
prizes =
religion = |footnotes = |

Henry Gwyn Jeffreys Moseley (November 23, 1887August 10, 1915) was an English physicist. His main contributions to science were the quantitative justification of the previously empirical concept of atomic number, and Moseley's law. This law advanced chemistry by immediately sorting the elements of the periodic table in a more logical order . It also advanced basic physics by providing independent support for the Bohr model of the Rutherford/Antonius Van den Broek nuclear atom containing positive nuclear charge equal to atomic number.


Henry Moseley was born in Weymouth, Dorset, on the south west coast of England in 1887. His father Henry Nottidge Moseley was a naturalist, a Professor of Anatomy and physiology at Oxford and a member of the Challenger Expedition. [ [http://www.chemcool.com/biography/moseley.htm Brief biography of Moseley] ] His mother was Amabel, daughter of the conchologist John Gwyn Jeffreys [She later married William Johnson Sollas, Professor of Geology at Oxford. She was also the British Ladies' Chess Champion of 1913] . He attended Eton College on a King's scholarship. [cite journal| title = The Work of H. G. J. Moseley | author = John L. Heilbron | journal = Isis | volume = 57 | issue = 3 | year = 1966 | pages = 336 – 364 | url = http://links.jstor.org/sici?sici=0021-1753%28196623%2957%3A3%3C336%3ATWOHGJ%3E2.0.CO%3B2-O| doi = 10.1086/350143 - JSTOR article; permission required] In 1906, he entered Trinity College of the University of Oxford, and on graduation from that institution in 1910 went to Manchester University to work with Ernest Rutherford. During his first year at Manchester, he had a full teaching load, but after a year he was relieved of his teaching duties and began full-time research.

In 1913, by using x-ray spectra obtained by diffraction in crystals, he found a systematic relation between wavelength and atomic number, Moseley's law. Previous to this, atomic numbers or elemental numbers had been thought of as a semi-arbitrary sequential ordering-number, based on sequence of atomic masses, but altered when necessary (for example, by Dimitri Mendeleev) to put an element in the appropriate place in the periodic table. For example, cobalt and nickel had been assigned atomic numbers of 27 and 28, respectively, based on their chemical properties, since they have nearly identical atomic mass (in fact, cobalt's atomic mass is larger than nickel's, which would have reversed them had they been placed in the periodic table strictly according to this criterion). Moseley's experiments were able to show directly that cobalt and nickel have clearly differing atomic numbers of 27 and 28, and are correctly placed in the periodic table by an objective measure. Moseley's discovery thus showed that atomic numbers were not arbitrary, but have an experimentally measurable basis.

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 very rare elements technetium and promethium, and the last two discovered naturally-occurring stable elements hafnium (discovered 1923) and rhenium (discovered 1925). None were known in Moseley's time. Mendeleev had previously predicted technetium, and Bohuslav Brauner had previously predicted promethium; Moseley confirmed their predictions, predicted the two additional undiscovered elements, and argued that there were no other gaps in the periodic table between aluminum and gold.

This last matter had been an issue, particularly with the rare earths. Moseley was able to demonstratethat the lanthanoid series of rare-earth elements, i.e. lanthanum through lutetium inclusive, must have 15 members -- no more and no less. The number of lanthanoids was an issue very far from being settled by the chemistry of that time, which could not yet provide pure samples of all the rare earth salts, and in some cases was chemically unable to tell mixtures of two very similar elements from pure materials. Moseley's instrument was able to sort out these problems, some of which had occupied chemists for years, almost immediately. He predicted the existence of element 61, a lanthanoid whose existence was previously unsuspected.(Many years later element 61 i.e. promethium was created artificially.) [ [http://portal.acs.org/portal/acs/corg/content?_nfpb=true&_pageLabel=PP_ARTICLEMAIN&node_id=925&content_id=CTP_004295&use_sec=true&sec_url_var=region1 American Chemical Society, "Separation of Rare Earth Elements"] ]

In 1914, Moseley resigned at Manchester to return to Oxford to pursue his research, but when World War I broke out, he turned down a job offer and enlisted in the Royal Engineers. He fought at Gallipoli, where he was killed in action by a sniper in 1915, shot through the head while in the act of telephoning an order. Many speculated that he should have won the Nobel Prize, but was unable to because it is only awarded to the living. It is speculated that because of Moseley's death in the War that the British and other world governments began a policy of no longer allowing their scientists to enlist for combat.

Only twenty-seven years old at death, Moseley could in many scientists' opinions have contributed much to the knowledge of atomic structure had he lived. As Niels Bohr once said in 1962, "You see actually the Rutherford work [the nuclear atom] was not taken seriously. We cannot understand today, but it was not taken seriously at all. There was no mention of it any place. The great change came from Moseley."

Contribution to our understanding

Previous to Moseley and his law, atomic numbers had been thought of as a semi-arbitrary ordering number, vaguely increasing with atomic weight but not strictly defined by it. Moseley's discovery showed that atomic numbers were not arbitrary but have a physical basis. He redefined the idea of atomic numbers from its previous status as an around-about approximate numerical tag to help sorting, i.e. in the periodic table, into a real and objective whole-number quantity which was experimentally directly measurable. Furthermore, as noted by Bohr, Moseley's law provided a reasonably complete experimental set of data supporting the (at that time new from 1911) Ernest Rutherford/Antonius Van den Broek concept of the atom, in which atomic number is understood as representing physically exactly the number of positive charges (protons) in a central atomic nucleus (Moseley mentions these two scientists in his paper, but does not actually mention Bohr). A simple modification of Rydberg and Bohr's formula was found to give Moseley's empirically-derived law for measurement of atomic number.

Use of X-ray spectrometer

X-ray spectrometers as Moseley knew them worked as follows: A glass-bulb electron tube similar to that held by Moseley in the photo above, was used. Inside the evacuated tube, electrons were fired at a substance (i.e. a sample of pure element in Moseley's work), causing ionisation of a core electron. Decay of the core hole then led to emission of x-rays which were led out of the tube in a semi-beam, through an opening in the external X-ray shielding, then diffracted by a standard salt crystal, with angular results read out as lines by exposure of an X-ray film plate fixed outside the vacuum tube, at a known distance. Application of Bragg's law (after a guess at the mean distance between atoms in a crystal, based on density) then allowed the wavelength and thus frequency of the emitted x-rays to be determined. Moseley participated in the design and development of early X-ray specrometry equipment, learning some techniques from Sir W.H. Bragg at Leeds, and developing others himself. Many techniques were copied from principles used with light spectrometers, by substituting crystals, ionization chambers and photographic plates for the analogous equipment. In some cases Moseley was forced to modify the equipment to detect particularly soft X-rays which would not penetrate air and paper, by working with completely evacuated equipment, and in the dark.

References and notes

Further reading




External links

* [http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Moseley-article.html Moseley's original articles]
* [http://alsos.wlu.edu/qsearch.aspx?browse=people/Moseley,+Henry Some books related to Moseley and his work (from the Alsos Digital Library)]
* [http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/moseley.html Moseley plot of characteristic x-rays]

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Henry Moseley — en su laboratorio. Esta rara imagen es la única fotografía que no es un retrato del científico. Henry Gwyn Jeffreys Moseley (23 de noviembre de 1887 – 10 de agosto de 1915) fue un físico y químico inglés. Su principal contribución a la ciencia,… …   Wikipedia Español

  • Henry Moseley — Henry Gwyn Jeffreys Moseley (* 23. November 1887 in Weymouth, England; † 10. August 1915 in Gallipoli, Türkei) war ein britischer Physiker. Sein wichtigster wissenschaftlicher Beitrag war der Beweis der Richtigkeit des Konzeptes der Or …   Deutsch Wikipedia

  • Henry Moseley — Pour les articles homonymes, voir Moseley. Henry Moseley Henry Gwyn Jeffreys Moseley, né le 23 novembre 1887 à Weymouth …   Wikipédia en Français

  • Henry Moseley — n. Henry Gwyn Jeffreys Moseley (1887 1915), British physicist who deduced that the atomic number (number of protons within a nucleus) of an element can be determined from the element s x ray spectrum …   English contemporary dictionary

  • Henry Nottidge Moseley — Nacimiento 14 de noviembre 1844 Wandsworth Fallecimiento 10 de noviembre 1891, 46 años Residencia Gran Bretaña Nacionalidad …   Wikipedia Español

  • Henry Gwyn Jeffreys Moseley — Henry Moseley Henry Moseley Henry Gwyn Jeffreys Moseley est un physicien britannique né le 23 novembre 1887 et décédé le 10 août 1915. Son père était le naturaliste Henry Nottidge Moseley. L ordre des éléments dans le tableau périodique a été… …   Wikipédia en Français

  • Henry Nottidge Moseley — était un naturaliste britannique, né le 14 novembre 1844 à Wandsworth et mort le 10 novembre 1891. Il était le fils d’Henry Moseley. Il étudia à Harrow School et obtint son Bachelor of Arts en 1868 à Oxford puis son Master of Arts en 1872. Il… …   Wikipédia en Français

  • Moseley (disambiguation) — Moseley is a suburb of Birmingham, England; formerly a village in Worcestershire. Moseley may also refer to: Moseley Rugby Football Club, based in Birmingham, England Moseley, California Bill Moseley, American actor Doug Moseley (born 1928),… …   Wikipedia

  • Moseley — ist der Familienname folgender Personen: Bill Moseley (* 1951), US amerikanischer Schauspieler Carol Moseley Braun (* 1947), US amerikanische Politikerin Dustin Moseley (* 1981), US amerikanischer Baseballspieler Henry Moseley (1887–1915),… …   Deutsch Wikipedia

  • Henry Bernard Chalon — (1770–1849) was an English painter and lithographer.LifeSon of the Dutch émigré and engraver Jan Chalon (1749–95), Henry studied at the Royal Academy Schools and then started specializing in sporting and animal painting. He was appointed Animal… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”