Henry Moseley was an English experimental physicist. In 1913 he used self-built equipment to prove that every element's identity is uniquely determined by the number of protons it has. His discovery revealed the true basis of the periodic table and enabled Moseley to predict confidently the existence of four new chemical elements, all of which were found.
Background
Henry Gwyn Jeffreys Moseley was born on November 23, 1887, in the town of Weymouth, United Kingdom.
His father, Henry Nottidge Moseley, was a biologist and part of the Challenger Expedition, which laid the groundwork for much of modern oceanography. His mother, Amabel Gwyn Jeffreys Moseley, was the daughter of a mollusk 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 catalog.
Education
Henry Moseley was educated in private schools. His first school was Summer Fields School - an elementary school. There he won a scholarship for Eton College, which is probably Britain's most prestigious high school.
Some time after arriving at Eton he decided the school's physics lessons were too easy, so he worked on the subject independently. Aged 18, he won Eton's physics and chemistry prizes.
Already a high achiever, he was admitted in 1906 to the University of Oxford's Trinity College, where he studied physics. There he disappointed himself. He was suffering badly from hayfever when he sat his final exams. He got a second class honors degree in physics, not the "first" he had hoped for and expected.
In the year 1910, Moseley joined Manchester University and worked as a graduate teacher at the institute, in his very first year, under the venerable Sir Ernest Rutherford. Although he was offered the job of a research assistant, he declined it as he had planned to return to Oxford three years later.
It was in 1913 that Moseley first devised the concepts that would go on to become the famous Moseley's Law. He used X-ray spectroscopy in order to measure the wavelength of an x-ray and then derived a relation of those with atomic numbers of an element.
In the year 1913, Henry Moseley decided to return to his alma mater the University of Oxford in order to work as a research scholar. However, in this regard, it is important to point out that Oxford did not offer him any stipend but gave him access to a modern laboratory.
During Moseley's time, Mendeleev's Periodic Table was regarded as the authoritative source of information on elements and atomic numbers; however, in the year 1914, he successfully demonstrated that there was a gap. Moseley published all of those findings in his famous paper.
In 1914 Rutherford and Bragg recommended to the University of Oxford that Moseley should be appointed to a chair of physics that was becoming vacant there. Moseley, however, had other ideas. When World War I began in 1914 he enlisted as a volunteer in the British Army's Royal Engineers. His family pleaded with him to continue his scientific research, and the army was reluctant to accept him. Moseley had to fight hard to get into the army.
Second Lieutenant Henry Moseley was killed in battle at the age of 27 in Gallipoli, Turkey on August 10, 1915.
In 1916 no Nobel Prizes were awarded in physics or chemistry. There is a strong scientific consensus that Henry Moseley, had he been alive, would have received one of these awards.
In the year 1919, Henry Moseley was awarded the Matteucci Medal, named after the Italian physicist of the same name and adjudicated by the Italian Society of Sciences. He won the award posthumously for his contribution to physics and chemistry.
Henry Moseley was an English physicist who contributed to atomic theory and lived from 1887 to 1915. His work with x-ray spectroscopy, in which electrons are fired at a metal plate, causing the atoms of metal to emit x-rays, allowed us to accurately measure the atomic number, which tells us the number of protons in an atom of any given element, of each element. In his research, he coined Moseley's Law, which is: the frequency of x-ray radiation has a precise mathematical relationship to an element's atomic number.
His research adds much to the work done by Dmitri Mendeleev, a Russian chemist and creator of Periodic Law who organized the periodic table by weight and properties because it also showed that organizing elements by the atomic number on the periodic table is the most accurate and reliable way to do so. This is because an element's atomic number tells us the number of protons in its nucleus and that number never changes, which takes care of the problem brought on by isotopes, which have different numbers of neutrons.
In 1919, Henry Moseley was awarded the Matteucci Medal posthumously.
Religion
There is no information about Henry Moseley's religious beliefs.
Politics
Henry Moseley decided to contribute to the war effort and joined the British Army during the First World War.
Views
In Rutherford's lab, Moseley began by studying radioactivity. However, this never quite 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 Charles Galton 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 by x-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.
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 called Moseley's Law and allowed scientists a new, more accurate way to organize elements. His method was so accurate that it 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.
Early versions of the periodic table were less than exact in their placement of elements. In the late 18th century, Antoine Lavoisier categorized them by properties as either gases, metals, non-metals, or earths. As scientists obtained more accurate atomic weights and new elements were discovered, the periodic table began to more closely resemble the today periodic table. Dimitry Mendeleev, a Russian chemist and creator of Periodic Law, organized the elements by atomic weight and properties in 1869. His table formed the basis for the one scientists still use.
Today, the periodic table is familiar to anyone who's studied chemistry. It's an enormously useful organizational tool that places elements based on their atomic numbers and properties. The atomic number tells us the number of protons in an atom of any given element. This number never changes, while the number of neutrons may vary in the case of isotopes, and its electrons in the case of ions. This makes the atomic number ideal for classifying elements.
While Mendeleev's periodic table was a huge leap forward, Henry Moseley's addition of the atomic number was what truly brought scientists the modern periodic table. Atomic weight generally follows the same pattern as atomic number, but it fails to account for isotopes, making the atomic number more reliable and precise.
Quotations:
"We have here a proof that there is in the atom a fundamental quantity, which increases by regular steps as one passes from one element to the next. This quantity can only be the charge on the central positive nucleus, of the existence of which we already have definite proof."
