Henry Moseley at work. Henry Nottidge Moseley ( 14 november 1844 - 10 november 1891) was a British naturalist. This rare image is the only non-portrait photograph known of the physicist.

Henry Gwyn Jeffreys Moseley (November 23, 1887 – August 10, 1915) was an English physicist. Events 800 - Charlemagne arrives at Rome to investigate the alleged crimes of Year 1887 ( MDCCCLXXXVII) was a Common year starting on Saturday (link will display the full calendar of the Gregorian calendar (or a Common Events 612 BC - Killing of Sinsharishkun, King of Assyrian Empire Year 1915 ( MCMXV) was a Common year starting on Friday (link will display the full calendar of the Gregorian calendar (or a Common year England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. His main contributions to science were the quantitative justification of the previously empirical concept of atomic number, and Moseley's law. Science (from the Latin scientia, meaning " Knowledge " or "knowing" is the effort to discover, and increase human understanding See also List of elements by atomic number In Chemistry and Physics, the atomic number (also known as the proton Moseley's law is an Empirical law concerning the characteristic x-rays that are emitted by Atoms It is historically important in quantitatively justifying This law advanced chemistry by immediately sorting the elements of the periodic table in a more logical order. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties 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. In Atomic physics, the Bohr model created by Niels Bohr depicts the Atom as a small positively charged nucleus surrounded by Electrons Ernest Rutherford 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937 was a New Zealand Physicist Antonius van den Broek ( May 4, 1870 - October 25, 1926) was a Dutch amateur physicist (a real estate lawyer by training

Biography

Henry Moseley was born in Weymouth, Dorset, on the south west coast of England in 1887. Weymouth (ˈweɪməθ is a town in Dorset, England situated on a sheltered bay at the mouth of the River Wey on the English Channel coast Dorset ( (or archaically, Dorsetshire) is a county in South West England on the English Channel coast His father Henry Nottidge Moseley was a naturalist, a Professor of Anatomy and physiology at Oxford and a member of the Challenger Expedition. Henry Nottidge Moseley ( 14 november 1844 - 10 november 1891) was a British naturalist. Anatomy (from the Greek anatomia, from ana separate apart from and temnein, to cut up cut open is a branch of Biology that is the consideration Oxford is currently bidding for the 2010 Wikimania Conference Oxford () is a city, and the County town of Oxfordshire, The Challenger Expedition was a scientific expedition that made many discoveries to lay the foundation of Oceanography. ^[1] His mother was Amabel, daughter of the conchologist John Gwyn Jeffreys^[2]. Conchology is the scientific, semi-scientific or Amateur study of mollusk shells (in the UK spelled mollusc shells John Gwyn Jeffreys ( 18 January 1809 &ndash 21 January 1885) was a British Conchologist and Malacologist. He attended Eton College on a King's scholarship. Eton College, or just Eton, is a world-famous British Independent school for boys founded in 1440 by King Henry VI. ^[3] 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. Year 1906 ( MCMVI) was a Common year starting on Monday (link will display full calendar of the Gregorian calendar (or a Common year starting The College of the Holy and Undivided Trinity in the University of Oxford of the foundation of Sir Thomas Pope (Knight, or Trinity College for short is one of the The University of Oxford (informally "Oxford University" or simply "Oxford" located in the city of Oxford, Oxfordshire, England is the The University of Manchester is a " red brick " civic University located in Manchester, England. Ernest Rutherford 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937 was a New Zealand Physicist 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. Research is defined as Human activity based on Intellectual application in the investigation of Matter.

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. Year 1913 ( MCMXIII) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or a Common X-radiation (composed of X-rays) is a form of Electromagnetic radiation. The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. Moseley's law is an Empirical law concerning the characteristic x-rays that are emitted by Atoms It is historically important in quantitatively justifying 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. The atomic mass (ma is the Mass of an atom most often expressed in unified atomic mass units The atomic mass may be considered to be the total mass Dmitri Ivanovich Mendeleev (sometimes spelled Mendeleyev; Дми́трий Ива́нович Менделе́ев) ( &ndash) was a Russian chemist and A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. The periodic table of the chemical elements is a tabular method of displaying the Chemical elements Although precursors to this table exist its invention is 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). Cobalt (ˈkoʊbɒlt is a hard lustrous silver-grey Metal, a Chemical element with symbol Co. Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 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). Technetium (tɛkˈniːʃɪəm is the lightest Chemical element with no Stable isotope. Promethium (prəˈmiːθiəm/ /proʊˈmiːθiəm is a Chemical element with the symbol Pm and Atomic number 61 Hafnium (ˈhæfniəm is a Chemical element that has the symbol Hf and Atomic number 72 Rhenium (ˈriːniəm is a Chemical element with the symbol Re and Atomic number 75 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 order, and argue for, the separate existence of each of the 14 (and importantly, no more and no less) so-called lanthanide series of rare-earth elements, which follow lanthanum. Terminology The Trivial name " Rare earths " is sometimes used to describe all the lanthanoids together with Scandium and Yttrium Lanthanum (ˈlænθənəm is a Chemical element with the symbol La and Atomic number 57 The number of lanthanides was an issue very far from being settled chemically by the science 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.

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. Year 1914 ( MCMXIV) was a Common year starting on Thursday (link will display the full calendar of the Gregorian calendar (or a Common year World War I (abbreviated WWI; also known as the First World War, the Great War, and the War to End All The Corps of Royal Engineers, usually just called the Royal Engineers ( RE) and commonly known as the Sappers, is one of the corps 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. The Nobel Prize (Nobelpriset (Nobelprisen is a Swedish prize established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Peace, Literature 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. Niels Henrik David Bohr (nels ˈb̥oɐ̯ˀ in Danish 7 October 1885 – 18 November 1962 was a Danish Physicist who made fundamental contributions to understanding 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). Moseley's law is an Empirical law concerning the characteristic x-rays that are emitted by Atoms It is historically important in quantitatively justifying Ernest Rutherford 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937 was a New Zealand Physicist Antonius van den Broek ( May 4, 1870 - October 25, 1926) was a Dutch amateur physicist (a real estate lawyer by training The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive 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. Ionization is the physical process of converting an Atom or Molecule into an Ion by adding or removing charged particles such as Electrons 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. In Physics, Bragg's law is the result of experiments into the Diffraction of X-rays or neutrons off Crystal surfaces at certain angles 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. Sir William Henry Bragg OM, KBE (2 July 1862 – 10 March 1942 was a British Physicist and Chemist who uniquely shared the 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

• Heilbron, John L. (1974). John L Heilbron ( J L Heilbron) is an American historian of science best known for his work in the History of physics and the History H. G. J. Moseley: The Life and Letters of an English Physicist, 1887-1915. Berkeley and Los Angeles, California: University of California Press. ISBN 0-520-02375-7.  

• Jaffe, Bernard (1971). Moseley and the Numbering of the Elements. Garden City, New York: Anchor Books.  

• Scerri, Eric R. (2007). The Periodic Table: Its Story and Its Significance. Oxford: Oxford University Press.  

External links

• Moseley's original articles
• Some books related to Moseley and his work (from the Alsos Digital Library)
• Moseley plot of characteristic x-rays