Editing J. J. Thomson (section)

===Discovery of the electron===
Several scientists, such as [[William Prout]] and [[Norman Lockyer]], had suggested that atoms were built up from a more fundamental unit, but they envisioned this unit to be the size of the smallest atom, hydrogen. Thomson in 1897 was the first to suggest that one of the fundamental units of the atom was more than 1,000 times smaller than an atom, suggesting the subatomic particle now known as the electron. Thomson discovered this through his explorations on the properties of cathode rays. Thomson made his suggestion on 30 April 1897 following his discovery that cathode rays (at the time known as [[Philipp Lenard|Lenard rays]]) could travel much further through air than expected for an atom-sized particle.<ref name="referenceB">{{cite journal |last=Thomson |first=J.J. |year=1897 |url=https://books.google.com/books?id=vBZbAAAAYAAJ&pg=PA104 |title=Cathode Rays |journal=The Electrician |volume=39 |page=104}}</ref> He estimated the mass of cathode rays by measuring the heat generated when the rays hit a thermal junction and comparing this with the magnetic deflection of the rays. His experiments suggested not only that cathode rays were over 1,000 times lighter than the hydrogen atom, but also that their mass was the same in whichever type of atom they came from. He concluded that the rays were composed of very light, negatively charged particles which were a universal building block of atoms. He called the particles "corpuscles", but later scientists preferred the name [[electron]] which had been suggested by [[George Johnstone Stoney]] in 1891, prior to Thomson's actual discovery.<ref>{{cite book |last=Falconer |first=Isobel  |year=2001 |chapter=Corpuscles to electrons |chapter-url=https://isobelf.files.wordpress.com/2013/08/falconer_corpusclestoelectrons_preprint.pdf |editor1-last=Buchwald |editor1-first=J. Z.|editor2-last=Warwick |editor2-first=A. |title=Histories of the Electron |publisher=MIT Press |pages=77–100 |isbn=978-0262024945}}</ref>

In April 1897, Thomson had only early indications that the cathode rays could be deflected electrically (previous investigators such as [[Heinrich Hertz]] had thought they could not be). A month after Thomson's announcement of the corpuscle, he found that he could reliably deflect the rays by an electric field if he evacuated the discharge tube to a very low pressure. By comparing the deflection of a beam of cathode rays by electric and magnetic fields he obtained more robust measurements of the mass-to-charge ratio that confirmed his previous estimates.<ref name="PhilMag">{{cite journal|last1=Thomson|first1=J. J.|title=Cathode Rays|journal=Philosophical Magazine|date=7 August 1897|volume=44|issue=269|page=293|url=https://zenodo.org/records/1431235/files/article.pdf|access-date=4 August 2014|series=5|doi=10.1080/14786449708621070}}</ref> This became the classic means of measuring the charge-to-mass ratio of the electron. Later in 1899 he measured the charge of the electron to be of {{val|6.8|e=−10|u=esu}}.<ref>{{cite journal |last1=Thomson |first1=J.J. |title=On the masses of the ions in gases at low pressures |journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science |date=1899 |volume=48 |issue=295 |pages=547–567 |doi=10.1080/14786449908621447 |url=https://www.tandfonline.com/doi/abs/10.1080/14786449908621447 |access-date=28 December 2024}}</ref>

Thomson believed that the corpuscles emerged from the atoms of the trace gas inside his [[cathode-ray tube]]s. He thus concluded that atoms were divisible, and that the corpuscles were their building blocks. In 1904, Thomson suggested a model of the atom, hypothesizing that it was a sphere of positive matter within which electrostatic forces determined the positioning of the corpuscles.<ref name="Profile" /> To explain the overall neutral charge of the atom, he proposed that the corpuscles were distributed in a uniform sea of positive charge.  In this "[[plum pudding model]]", the electrons were seen as embedded in the positive charge like raisins in a plum pudding (although in Thomson's model they were not stationary, but orbiting rapidly).<ref>{{citation|title=Modern Inorganic Chemistry|first=Joseph William|last=Mellor|publisher=Longmans, Green and Company|year=1917|page=868|url=https://books.google.com/books?id=1iQ7AQAAMAAJ&pg=PA868|quote=According to J. J. Thomson's hypothesis, atoms are built of systems of rotating rings of electrons.}}</ref><ref>{{harvtxt|Dahl|1997}}, p. 324: "[https://books.google.com/books?id=xUzaWGocMdMC&pg=PA324 Thomson's model, then, consisted of a uniformly charged sphere of positive electricity (the pudding), with discrete corpuscles (the plums) rotating about the center in circular orbits, whose total charge was equal and opposite to the positive charge.]"</ref>

Thomson made the discovery around the same time that [[Walter Kaufmann (physicist)|Walter Kaufmann]] and [[Emil Wiechert]] discovered the correct mass to charge ratio of these cathode rays (electrons).<ref>{{cite journal |last1=Chown |first1=Marcus |title=Forum: Just who did discover the electron? |journal=New Scientist |date=29 March 1997 |issue=2075 |url=https://www.newscientist.com/article/mg15320756-400-forum-just-who-did-discover-the-electron-marcus-chown-says-the-truth-is-not-quite-as-the-history-books-suggest/ |access-date=17 October 2020 |quote=Marcus Chown says the truth is not quite as the history books suggest.}}</ref>

The name "electron" was adopted for these particles by the scientific community, mainly due to the advocation by [[George Francis FitzGerald]], [[Joseph Larmor]], and [[Hendrik Lorentz]].<ref name=OHara1975>
{{cite journal
 | last =O'Hara
 | first =J. G.
 | title =George Johnstone Stoney, F.R.S., and the Concept of the Electron
 | journal =Notes and Records of the Royal Society of London
 | volume =29
 | issue =2
 | pages =265–276
 | publisher =Royal Society
 | date =March 1975
 | jstor =531468
 | doi =10.1098/rsnr.1975.0018
 | s2cid =145353314
}}</ref>{{rp|273}} The term was originally coined by [[George Johnstone Stoney]] in 1891 as a tentative name for the basic unit of electrical charge (which had then yet to be discovered).<ref>{{cite journal |author=George Johnstone Stoney |year=1891 |title=On the Cause of Double Lines and of Equidistant Satellites in the Spectra of Gases |journal=The Scientific Transactions of the Royal Dublin Society |volume=4 |pages=583–608 |url=https://digitalarchive.rds.ie/files/show/4769}}</ref><ref>{{cite journal |journal=Philosophical Magazine |author=George Johnstone Stoney |date=1894 |title=Of the "Electron", or Atom of Electricity |series=Series 5 |volume=38 |issue=233 |pages=418–420 |url=https://archive.org/details/londonedinburgh5381894lon/page/418/mode/2up}}</ref> For some years Thomson resisted using the word "electron" because he didn't like how some physicists talked of a "positive electron" that was supposed to be the elementary unit of positive charge just as the "negative electron" is the elementary unit of negative charge. Thomson preferred to stick with the word "corpuscle" which he strictly defined as negatively charged.<ref>{{cite journal |year=1907 |author=J. J. Thomson |title=The Modern Theory of Electrical Conductivity of Metals |journal=Journal of the Institution of Electrical Engineers |volume=38 |issue=183 |pages=455–468|doi=10.1049/jiee-1.1907.0026 |url=https://books.google.com/books?id=Ni9HAQAAMAAJ&pg=PA467}}: "Perhaps I can best show my appreciation by trying to answer the questions which Professor Silvanus Thompson addressed to me. I think his first question was a question rather of notation, as to the difference between the electron and the corpuscle. I prefer the corpuscle for two reasons: first of all, it is my own child, and I have a kind of parental affection for it; and, secondly, I think it has one merit which the term electron has not. We talk about positive and negative electrons, and I think when you use the same term for the two the suggestion is that there is an equality, so to speak, in the properties. From my point of view the difference between the negative and the positive is essential, and much greater than I think would be suggested by the term positive electron and negative electron. Therefore I prefer to use a special term for the negative units and call it a corpuscle. A corpuscle is just a negative electron."</ref> He relented by 1914, using the word "electron" in his book ''The Atomic Theory''.<ref>{{cite book |author=J. J. Thomson |year=1914 |title=The Atomic Theory |publisher=Oxford Clarendon Press |url=https://archive.org/details/atomictheorythom00thomrich/page/n3/mode/2up}}</ref> In 1920, Rutherford and his fellows agreed to call the nucleus of the hydrogen ion "proton", establishing a distinct name for the smallest known positively-charged particle of matter (that can exist independently anyway).<ref>{{cite journal |author=Orme Masson |date=1921 |title=The Constitution of Atoms |journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science |volume=41 |issue=242 |pages=281–285 |doi=10.1080/14786442108636219 |url=https://zenodo.org/records/1430963/files/article.pdf%3Fdownload%3D1&ved=2ahUKEwjN-YzeqIiGAxVyUqQEHaM_COwQFnoECBwQAQ&usg=AOvVaw1G76aUFXByKGSDekUwv2sa}}<br/>Footnote by Ernest Rutherford: 'At the time of writing this paper in Australia, Professor Orme Masson was not aware that the name "proton" had already been suggested as a suitable name for the unit of mass nearly 1, in terms of oxygen 16, that appears to enter into the nuclear structure of atoms. The question of a suitable name for this unit was discussed at an informal meeting of a number of members of Section A of the British Association [for the Advancement of Science] at Cardiff this year. The name "baron" suggested by Professor Masson was mentioned, but was considered unsuitable on account of the existing variety of meanings. Finally the name " proton" met with general approval, particularly as it suggests the original term "protyle " given by Prout in his well-known hypothesis that all atoms are built up of hydrogen. The need of a special name for the nuclear unit of mass 1 was drawn attention to by Sir Oliver Lodge at the Sectional meeting, and the writer then suggested the name "proton."'</ref>