Editing History of atomic theory (section)

==Discovery of isotopes==
{{Main|Isotope}}
While experimenting with the products of [[radioactive decay]], in 1913 [[radiochemistry|radiochemist]] [[Frederick Soddy]] discovered that there appeared to be more than one variety of some elements.<ref>{{cite web
|url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1921/soddy-bio.html
|title=Frederick Soddy, The Nobel Prize in Chemistry 1921
|publisher=Nobel Foundation
|access-date=2008-01-18
}}</ref> The term [[isotope]] was coined by [[Margaret Todd (doctor)|Margaret Todd]] as a suitable name for these varieties.<ref>{{cite journal|last=Fleck |first=Alexander |year=1957|title=Frederick Soddy|journal=Biographical Memoirs of Fellows of the Royal Society|volume=3|pages=203–216|quote=p. 208:  Up to 1913 we used the phrase 'radio elements chemically non-separable' and at that time the word isotope was suggested in a drawing-room discussion with Dr. Margaret Todd in the home of Soddy's father-in-law, Sir [[George Beilby]].|doi=10.1098/rsbm.1957.0014|doi-access=free}}</ref>

That same year, [[J. J. Thomson]] conducted an experiment in which he channeled a stream of [[neon]] [[ion]]s through magnetic and electric fields, striking a photographic plate at the other end. He observed two glowing patches on the plate, which suggested two different deflection trajectories. Thomson concluded this was because some of the neon ions had a different mass.<ref name="thompson3">{{cite journal|author=Thomson, J. J. |url=http://web.lemoyne.edu/~giunta/canal.html | doi = 10.1098/rspa.1913.0057 |title=Rays of positive electricity|journal=Proceedings of the Royal Society|year=1913|volume=A 89|pages=1–20|bibcode = 1913RSPSA..89....1T|issue=607 |s2cid=124295244 |doi-access=|url-access=subscription}} [as excerpted in Henry A. Boorse & Lloyd Motz, ''The World of the Atom'', Vol. 1 (New York: Basic Books, 1966)]. Retrieved on August 29, 2007.</ref> The nature of this differing mass would later be explained by the discovery of [[neutron]]s in 1932: all atoms of the same element contain the same number of protons, while different isotopes have different numbers of neutrons.<ref>{{cite book|url=https://openstax.org/books/chemistry-2e/pages/21-1-nuclear-structure-and-stability |title=Chemistry 2e |publisher=OpenStax |first1=Paul |last1=Flowers |display-authors=etal |year=2022 |isbn=978-1-947172-61-6 |pages=70–71}}</ref>