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Master of Missing Elements See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/275701920 Master of Missing Elements Article in American Scientist · September 2014 DOI: 10.1511/2014.110.358 CITATION READS 1 93 1 author: Eric Robert Scerri University of California, Los Angeles 299 PUBLICATIONS 1,736 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: A Tale of Seven Scientists and A New Philosophy of Science View project Celebrating 150 years of Mendeleev's discovery and other chemistry blogs View project All content following this page was uploaded by Eric Robert Scerri on 07 November 2015. The user has requested enhancement of the downloaded file. A reprint from American Scientist the magazine of Sigma Xi, The Scientific Research Society This reprint is provided for personal and noncommercial use. For any other use, please send a request to Permissions, American Scientist, P.O. Box 13975, Research Triangle Park, NC, 27709, U.S.A., or by electronic mail to [email protected]. ©Sigma Xi, The Scientific Research Society and other rightsholders Master of Missing Elements Henry Moseley’s discoveries sorted out the periodic table and transformed how scientists look for new forms of the most basic substances. Eric R. Scerri ust over 100 years ago, a young Henry Moseley seemed destined molecules) might be capable of diffract- English physicist named Henry to leave his mark on science. He was ing x-rays. This prediction was almost Moseley gave new life to the pe- born in the county of Dorset in Eng- immediately confirmed by indepen- riodic table of the elements, and land in 1887, into a family with an ex- dent researchers, who found that the Jhelped resolve a number of prob- traordinary scientific pedigree. Both of diffracted rays produced discrete lines lems in chemistry and physics. There his grandfathers as well as his father, on photographic film. is a good chance you have never heard who died when he was just four years The diffraction of x-rays differed of him. Soon after Moseley published old, were fellows of the Royal Society. based on the type of crystal used; the this work, World War I broke out, and One grandfather was a mathematician; pattern of lines could be precisely mea- the 27-year-old patriot felt compelled to the other and Moseley’s father were sured to obtain detailed information volunteer for service on the war front, zoologists. In 1901 the young Moseley about the distance between the planes where he was killed by a sniper’s bullet. earned a scholarship to study at Eton, of atoms that make up the crystals, un- Despite his abbreviated life, Moseley’s one of England’s most prestigious veiling their structure. Furthermore, a work continues to influence the world schools. There he excelled at academic British physicist, Charles Barkla, found of chemistry. In fact, his research is more work as well as sports; he also became that each element scattered x-rays to a influential than ever today, as new ele- infused with a patriotic spirit that different extent, producing distinctive ments are being synthesized and added eventually cost him his life. lines and thereby indicating the scat- to the periodic table, such as the yet-to- In 1906 Moseley gained another terer’s composition. Two other Brit- be-named elements 115 and 118. scholarship, this time to Trinity Col- ish physicists, Henry Bragg and his Moseley discovered a way to use lege at the University of Oxford. He son William, found that even reflection x-rays in a vacuum to identify the was disappointed with the lack of from crystals could be used to obtain atomic charge of elements (a critical interest in academic work in general useful information on the distances be- measurement of their chemical prop- and physics in particular at the college, tween planes of atoms. erties, now known to correspond to however. He noticed that pursuits At the same time, there was a great the number of electrons in each ele- such as fox hunting were regarded as deal of debate as to whether x-rays ment). His work allowed for the de- more important than academic excel- were waves or particles. The study finitive identification of substances, lence. After failing to gain a first-class of x-rays was one of the first areas of and revealed that several elements honors degree in physics—probably physics in which wave-particle duality— were missing from the periodic table because he was too interested in the the view that some phenomena might of the time, setting up subsequent re- subject matter rather than techniques be neither one nor the other but both searchers to make groundbreaking for passing exams—Moseley trans- together—began to take shape. That discoveries about the composition of ferred his studies to the University of same realization was eventually made the world. His methods also showed Manchester to work with Rutherford. of electrons, thus opening up the pos- the logic of the now standard ordering Rutherford immediately set Moseley sibility of treating the electron as a of the periodic table. Moseley worked to work on experiments with radioac- wave, as Erwin Schrödinger went on with some giants in physics, including tive isotopes, apparently recognizing to do. Modern ideas about quantum the legendary Ernest Rutherford, who his talents. But what really excited physics emerged from there. discovered the structure of the atom. It Moseley was another new area of phys- Henry Moseley followed all these is likely that Moseley would have won ics, one that had begun slightly before developments closely and asked Ruth- the Nobel Prize himself, if not for his the discovery of radioactivity. In 1897 erford if he too could initiate a pro- untimely death. the German physicist Wilhelm Röntgen gram of research on x-rays. Initially had discovered some mysterious rays Rutherford was reluctant to allow that he named x-rays, which found im- Moseley to discontinue his work on Eric R. Scerri has been researching and teaching at mediate applications in medicine as isotopes, but he relented after Bragg the University of California at Los Angeles for the past 15 years, both in chemistry and the philosophy well as basic scientific research. In 1912 the elder invited Moseley in October of science. He is also a book author, a public speaker, another German physicist, Max von 1912 to the University of Leeds to train and an avid blues guitarist. He received his Ph.D. Laue, proposed that crystals of inor- him in working with x-rays. On his in the history and philosophy of science from King’s ganic compounds (substances that are return to Manchester a month later, College London. Internet: www.ericscerri.com not based on carbon–hydrogen bonded Moseley teamed up with the math- 358 American Scientist, Volume 102 © 2014 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact [email protected]. Museum of the History Science, University Oxford ematician Charles Darwin (the grand- A young Henry Moseley, shown during his student days at Trinity College, holds laboratory son of the “right Darwin,” as the Dan- equipment similar to pieces he later used to make breakthrough discoveries about the ordering ish physicist Niels Bohr later described of the periodic table. Moseley’s career was cut short by his death during the Battle of Gallipoli him). Together Moseley and Darwin in 1915, but his work continues to influence elemental studies today. repeated the work of the Braggs and tried to extend it into new directions. when physics was undergoing great nucleus of a helium atom, consisting of After publishing a couple of articles discoveries about the atom. Sev- two protons and two neutrons), which together, Moseley rather mysteriously eral lines of research were begin- also scatter in patterns dependent on decided to return to Oxford, where he ning to illuminate the relationship the element. would work as an independent schol- between the electrical charge of the The next piece in this puzzle to ar, possibly awaiting an appointment nucleus and the atomic weight of any understand the elements came from at the university. Whatever the reason, particular element. Barkla’s experi- a most unlikely source, but proved the move to Oxford proved enormously ments, on the degree to which x-rays highly influential for Moseley and fruitful. It was after returning that Mose- were scattered by samples of differ- other researchers. A Dutch economist ley conducted his epoch-making work, ent elements, suggested that nuclear and amateur scientist, Anton van den which resolved a puzzle about the or- charge was approximately equal to Broek, had a long-standing interest in dering of the periodic table and which half of the atomic weight of any ele- the periodic table, and attempted to continues to be felt up to the present day. ment. Rutherford and his colleagues improve on Dmitri Mendeleev’s clas- came to exactly the same conclusion sic system of listing the chemical ele- Dawn of the Nuclear Era from their work bombarding elements ments. Van den Broek attempted vari- Moseley began his crucial experi- with highly energetic, radioactive al- ous improvements by drawing on the ment in the early 1900s, at a time pha particles (now understood as the results of Barkla and Rutherford. He www.americanscientist.org © 2014 Sigma Xi, The Scientific Research Society. Reproduction 2014 September–October 359 with permission only. Contact [email protected]. Atomic weights had Moseley’s results were his great also created three plac- breakthrough. He found that van den es in the periodic table Broek had been correct in assuming where a mysterious- that the elements are more properly looking anomaly had ordered using atomic charge, or atomic long bothered chem- number as it became known, than by ists.
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