Plum pudding model: Difference between revisions

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The '''plum pudding model''' was the first [[scientific modelling|scientific model]] of the [[atom]] to describe an internal structure. It was first proposed by [[J. J. Thomson]] in 1904 following his discovery of the [[electron]] in 1897, and was rendered obsolete by [[Ernest Rutherford]]'s discovery of the [[atomic nucleus]] in 1911. The model tried to account for two properties of atoms then known: that there are electrons, and that atoms have no net electric charge. Logically there had to be an equal amount of positive charge to balance out the negative charge of the electrons. As Thomson had no idea as to the source of this positive charge, he tentatively proposed that it was everywhere in the atom, and that the atom was spherical—this was the mathematically simplest hypothesis to fit the available evidence, or lack thereof. In such a sphere, the negatively charged electrons would distribute themselves in a more or less even manner throughout the volume, simultaneously repelling each other while being attracted to the positive sphere's center.<ref>{{harvnb|Thomson|1907|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>

Despite Thomson's attemptedefforts, without success to develop a completehis model that could predict other known properties of the atom,couldn't suchaccount asfor [[emission spectra]] and [[Valence (chemistry)|valencies]]. Based on experimental studies of [[Rutherford scattering experiments|alpha particle scattering]], [[Ernest Rutherford]] developed an alternative [[Rutherford model|model for the atom]] featuring a compact nucleus where the positive charge is concentrated.

Thomson's model is popularly referred to as the "plum pudding model" with the notion that the electrons are distributed uniformly like raisins in a [[plum pudding]]. Neither Thomson nor his colleagues ever used this analogy.<ref name="HonGoldstein2013">{{Cite journal |last1=Hon |first1=Giora |last2=Goldstein |first2=Bernard R. |date=6 September 2013 |title=J. J. Thomson's plum-pudding atomic model: The making of a scientific myth |url=https://onlinelibrary.wiley.com/doi/10.1002/andp.201300732 |journal=Annalen der Physik |volume=525 |issue=8–9 |pages=A129–A133 |bibcode=2013AnP...525A.129H |doi=10.1002/andp.201300732}}</ref> It seems to have been coined by popular science writers to make the model easier to understand for the layman. The analogy is perhaps misleading because Thomson likened the positive sphere to a liquid rather than a solid since he thought the electrons moved around in it.<ref>Letter from J. J. Thomson to Oliver Lodge dated 11 April 1904, quoted in {{harvnb|Davis|Falconer|1997|p=153}}:<br />