Editing Rutherford scattering experiments (section)

===Thomson's model of the atom===
[[File:Thomson atom seven electrons.svg|thumb|The "[[plum pudding model]]" of an atom with seven electrons, as imagined by [[J. J. Thomson]] in 1905]]
{{main | Plum pudding model}}
The prevailing model of atomic structure before Rutherford's experiments was devised by [[J.&nbsp;J.&nbsp;Thomson]].<ref name=GilibertiLovisetti/>{{rp|123}} Thomson had discovered the [[electron]] through his work on cathode rays<ref>{{cite journal |author=J. J. Thomson |url=http://web.lemoyne.edu/~GIUNTA/thomson1897.html |title=Cathode rays |journal=Philosophical Magazine |volume=44 |issue=269 |pages=293–316 |year=1897}}</ref> and proposed that they existed within atoms, and an electric current is electrons hopping from one atom to an adjacent one in a series. There logically had to be a commensurate amount of positive charge to balance the negative charge of the electrons and hold those electrons together. Having no idea what the source of this positive charge was, he tentatively proposed that the positive charge was everywhere in the atom, adopting a spherical shape for simplicity.<ref name=GilibertiLovisetti/>{{rp|123}}<ref>J. J. Thomson (1907). ''The Corpuscular Theory of Matter'', p. 103: "In default of exact knowledge of the nature of the way in which positive electricity occurs in the atom, we shall consider a case in which the positive electricity is distributed in the way most amenable to mathematical calculation, i.e., when it occurs as a sphere of uniform density, throughout which the corpuscles are distributed."</ref> Thomson imagined that the balance of electrostatic forces would distribute the electrons throughout this sphere in a more or less even manner. Thomson also believed the electrons could move around in this sphere, and in that regard he likened the substance of the sphere to a liquid.<ref>J. J. Thomson, in a letter to [[Oliver Lodge]] dated 11 April 1904, quoted in Davis & Falconer (1997):<br/>
"With regard to positive electrification I have been in the habit of using the crude analogy of a liquid with a certain amount of cohesion, enough to keep it from flying to bits under its own repulsion. I have however always tried to keep the physical conception of the positive electricity in the background because I have always had hopes (not yet realised) of being able to do without positive electrification as a separate entity and to replace it by some property of the corpuscles.<br/>
When one considers that, all the positive electricity does, on the corpuscular theory, is to provide an attractive force to keep the corpuscles together, while all the observable properties of the atom are determined by the corpuscles one feels, I think, that the positive electrification will ultimately prove superfluous and it will be possible to get the effects we now attribute to it from some property of the corpuscle.<br/>
At present I am not able to do this and I use the analogy of the liquid as a way of picturing the missing forces which is easily conceived and lends itself readily to analysis."</ref> The positive sphere was more of an abstraction than anything material. He did not propose a positively-charged subatomic particle; a counterpart to the electron.

Thomson was never able to develop a complete and stable model that could predict any of the other known properties of the atom, such as emission spectra and valencies.<ref>Thomson (1907). ''The Corpuscular Theory of Matter'', p. 106: "The general problem of finding how ''n'' corpuscles will distribute themselves inside the sphere is very complicated, and I have not succeeded in solving it"</ref> The Japanese scientist [[Hantaro Nagaoka]] rejected Thomson's model on the grounds that opposing charges cannot penetrate each other.<ref>[[#refDaintithGjertsen1999|Daintith & Gjertsen (1999)]], p. 395</ref> He proposed instead that electrons orbit the positive charge like the rings around [[Saturn]].<ref>{{cite journal
 |author1=Hantaro Nagaoka
 |year=1904
 |title=Kinetics of a System of Particles illustrating the Line and the Band Spectrum and the Phenomena of Radioactivity
 |url=http://www.chemteam.info/Chem-History/Nagaoka-1904.html
 |journal=[[Philosophical Magazine]] |series=Series 6
 |volume=7 |issue= 41|pages=445–455
 |doi=10.1080/14786440409463141
 |ref=refNagaoka1904
|url-access=subscription
 }}</ref> However this model was also known to be unstable.<ref name=Heilbron1968/>{{rp|303}}