Henry Gwyn Jeffreys Moseley
Henry Gwyn Jeffreys Moseley, commonly known as Harry Moseley, was a notable early 20th-century physicist born in 1887 in Dorset, England. He was the son of a prominent professor at Oxford and grew up in an academically enriched environment. Moseley studied physics at Oxford's Trinity College, where he later worked under renowned scientist Ernest Rutherford. His significant contributions to the field of physics and chemistry emerged through his research on X-ray diffraction techniques, which he utilized to explore the atomic structure of elements.
Moseley is best known for establishing the relationship between atomic number and nuclear charge, a groundbreaking insight that reorganized the periodic table based on atomic number rather than atomic weight. This discovery not only advanced the understanding of elemental properties but also allowed for the prediction of previously unknown elements. His work, encapsulated in Moseley's Law, laid foundational knowledge that would influence future atomic theory and the study of isotopes.
Tragically, Moseley’s promising career was cut short when he was killed in battle during World War I at the age of twenty-seven. His untimely death had a profound impact on both the military and scientific communities, prompting discussions about the value of retaining talented scientists during wartime. Moseley's legacy endures in the field of science, where he is remembered for his critical contributions and the potential he had yet to realize.
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Henry Gwyn Jeffreys Moseley
English physicist
- Born: November 23, 1887; Weymouth, England
- Died: August 10, 1915; Gallipoli, Turkey
Physicist Henry Moseley demonstrated the physics behind the chemical concept of the atomic number using X-ray spectroscopy. His discovery helped to define the modern periodic table, and helped to create a more complete understanding of the relationship between elements and atoms.
Also known as: Harry Moseley
Primary field: Physics
Specialty: Atomic and molecular physics
Early Life
Henry Gwyn Jeffreys Moseley, known as Harry Moseley to friends and colleagues, was born in 1887 in Dorset, a county in the southwest of England. He was one of three children born to Henry Nottidge Moseley, a professor of comparative anatomy at the University of Oxford, and Amabel Gwyn Jeffreys Moseley, daughter of renowned marine biologist John Gwyn Jeffreys. Moseley’s father participated in the Challenger expedition of 1872, a sea voyage that conducted soundings and dredges throughout the world, and discovered over 4,000 previously unknown species of marine life.
Moseley’s father died when he was four years old, and the family moved to the county of Surrey, where he attended the Summer Fields School, a boy’s preparatory academy associated with Eton College. Moseley was awarded a King’s Scholarship, which qualified him for entrance to Eton College at reduced fees. At Eton, Moseley studied under physicist T. C. Porter, one of the first English physicists to experiment with X-rays, and codiscoverer of the Ferry-Porter Law, which describes the optical phenomenon of flickering light.
Moseley entered Oxford University’s Trinity College in 1906, where he earned a degree in physics. After graduating, his performance in the college’s research laboratories earned him a position working at Manchester University in the laboratories of Ernest Rutherford, the New Zealand–born chemist and physicist who discovered the concept of radioactive half-life and decay. After a year of teaching, Moseley began working full-time on a research program investigating the X-ray diffraction techniques pioneered by German physicist Max Laue.
Life’s Work
Moseley’s interest in X-ray technology may have begun when he was studying at Eton with Porter. At this time, Australian physicists William Lawrence Bragg and William Henry Bragg were developing a method of using X-rays to investigate the structure of crystals. As X-rays are focused through a thin section of crystal, they are diffracted as they encounter atoms within the crystal matrix. Physicists then use photographic plates to detect the resulting X-rays. The pattern of diffracted rays is characteristic of the atomic structure of the material used as the diffraction medium. For a brief time, Moseley worked with William Lawrence Bragg at the University of Leeds, where he learned and refined techniques used in diffraction studies. The Braggs discovered X-ray diffraction in 1912, and the following year, Moseley began using their techniques to study various metals and other crystalline elements.
Moseley developed a system that allowed him to examine the diffraction patterns of various elements in quick succession. He began to notice patterns of relationships between the diffraction patterns of elements. Moseley was especially interested in the part of the diffraction pattern called “spectral lines,” which show up as dark or bright lines against an otherwise continuous spectrum. He noticed that when elements were examined in ascending order according to their atomic mass, the frequency of the spectral lines increased by what appeared to be a mathematically regular progression.
Moseley theorized that the essential characteristic represented by the observed variation in spectral lines was caused by differing charge within the nucleus of the atom. He hypothesized that the atoms of the periodic table could be arranged in terms of ascending nuclear charge instead of atomic weight, which was how the table was organized at the time.
Moseley’s discovery gave a physical justification for the ordering of elements into precise chemical families, organized by “atomic number,” rather than atomic mass or weight. It became evident upon the publication of Moseley’s research in 1913 that the atomic number was the most basic characteristic of the elements in question, varying according to a precise mathematical formula of increasing charge, rather than by the more variable increases in atomic mass between elements. In essence, Moseley proved the justification for the ordering scheme that was being widely used but lacked a clear explanation.
The precise nature of the increase in atomic number between elements also meant that Moseley was able to predict where there were elements missing from the periodic table, and he predicted the existence of atoms with atomic numbers 43 (technetium), 61 (promethium), 72 (hafnium) and 75 (rhenium). Moseley was further able to predict details of the spectral analysis for these missing elements, thereby providing a way for chemists to better search for missing elements. Moseley’s contributions to this idea are preserved in Moseley’s law, which describes the ways X-rays are emitted by atoms, taking multiple variables into account.
Impact
Moseley’s discovery of the relationship between atomic number and nuclear charge was a major milestone in chemistry and physics, helping chemists to understand the elements and helping to refine the model of nuclear relationships predicted by physicist Neils Bohr’s model of the atom. The atomic number is now defined as the number of protons present in the nucleus of an atom, and thereby gives a precise measurement of the element’s charge. This definition of atomic structure helped to refine the idea of isotopes, which are now precisely defined as atoms possessing the same atomic number, but differing in the number of neutron’s present within the nucleus. Because atomic mass and weight take into account the total number of both protons and neutrons, the difference in atomic mass between elements does not occur in a precise progression. Moseley’s discovery thereby gave chemists and physicists an organized method for ordering atoms according to their most basic shared characteristics.
When World War I began, Moseley had resigned his post at Manchester and returned to Oxford University. He enlisted in the British armed forces and became a member of the Royal Engineers. After training for eight months, he travelled to Gallipoli, Turkey, on a military assignment. During the Battle of Sulva Bay on June 15, 1915, Moseley was shot and killed by an enemy sniper.
Moseley died at the age of twenty-seven, having only begun his career. His death had significant repercussions within the military and scientific communities. Though he had yet to achieve any significant honors for his work, Moseley’s 1913 discovery was already recognized as a major achievement in physics. Many in the scientific community believed that he might have been awarded the 1916 Nobel Prize, especially as two previous Nobel Prizes had been awarded to William Henry Bragg and Max Laue for their work in spectroscopy and diffraction. Many have speculated on the potential contributions Moseley might have made had he not been killed in battle. Moseley’s death is cited as the motivating factor behind the British government’s decision to enact a policy preventing promising scientists from enlisting for active duty in the armed forces.
Bibliography
Brandt, Siegmund. The Harvest of a Century: Discoveries in Modern Physics in 100 Episodes. New York: Oxford UP, 2009. Print. Provides coverage of major discoveries in physics over the previous century. Includes a discussion of Moseley’s life and work and the impact of his theories of atomic number and nuclear charge.
Cobb, Cathy, and Harold Goldwhite. Creations of Fire: Chemistry’s Lively History from Alchemy to the Atomic Age. Cambridge, MA: Perseus, 1995. Print. Historical overview of chemistry presented to the general reader, including biographical and sociological information on major figures in chemistry history. Includes a discussion of Moseley’s discovery of the significance of the atomic number and the effect of this discovery in refining the periodic table created by Mendeleev.
Heilbron, John L. H. G. J. Moseley: The Life and Letters of an English Physicist. Berkeley: U of California P, 1974. Print. Biographical account of Moseley’s life and research written by one of the foremost authorities on the history of physics and chemistry. Presents detailed biographical information about Moseley’s life and family as well as analyses of his work and the effect of his death on the British scientific community.