7/23/2019 Physicist Henry Moseley Discovered the Atomic Number of Each Element

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Physicist Henry Moseley discovered the atomic number of each element using x-rays,

which lead to more accurate organization of the periodic table. We will cover his life

and discovery of the relationship between atomic number and x-ray frequency, known

as Moseley's Law.

Who Was Henry Moseley?

Henry Moseley (November 23, 1887 - August 10, 1915) was a brilliant physicist

whose life and career were cut tragically short when he was killed in World War I.

Had he lived, he most likely would have won a Nobel Prize for his work showing that

the periodic table is best organized by atomic number. Isaac Asimov has been widely

quoted as saying that Moseley's death was 'the single most costly death of the war'

because of what he might have gone on to accomplish.

 Henry Moseley in 1910.

Biography

Early Life and Education

Henry Moseley, called Harry by family and friends, was born on November 23, 1887

in Dorset, England. His father, Henry Nottidge Moseley, was a biologist and part of

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the Challenger Expedition, which laid the groundwork for much of modern

oceanography. His mother, Amabel Gwyn Jeffreys Moseley, was the daughter of a a

mollusc biologist. Moseley spent much of his childhood exposed to science, often

exploring the countryside with his sister and keeping track of whatever plants and

animals they found in a catalogue.

Moseley never lost his enthusiasm for discovery and went on to study physics at

Oxford University, earning his bachelor's degree in 1910. It was here that he

developed his experimental skills before continuing his studies in the laboratory of

Ernest Rutherford at Victoria University of Manchester. Ernest Rutherford was one of

the greatest physicists of his--or any--time and could provide a fertile environment for

a promising scientist.

Research

In Rutherford's lab, Moseley began by studying radioactivity. However, this neverquite captured his interest and he soon decided to investigate x-rays instead. Moseley

was a brilliant experimentalist but wisely decided to get some help when it came to

the complicated mathematics involved in studying x-rays. For this reason, he started

a collaboration with C.G. Darwin, mathematician and grandson of Charles Darwin.

In July 1913, a conversation with physicist Niels Bohr led to the suggestion that an

element's atomic number could be determined byx-ray spectroscopy. In x-ray

spectroscopy, electrons are fired at a metal plate, causing the atoms of metal to emit

x-rays. The wavelength and frequency of these x-rays are then recorded.

 An X-ray tube used by Henry Moseley.

Henry Moseley collected the x-ray spectra of a variety of elements and found that the

frequency of x-ray radiation has a precise mathematical relationship to an element's

atomic number. This relationship is now calledMoseley's Law and allowed scientists

a new, more accurate way to organize elements. His method was so accurate that it

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predicted the existence of elements that hadn't been discovered yet. In fact, it took

scientists 30 years to fill in all of his predictions.