Plum pudding model: Difference between revisions
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}}</ref> At the time, atoms were known to have no net electric charge. |
}}</ref> At the time, atoms were known to have no net electric charge. Thomson understood the size of the electron and it was widely accepted that atoms were electrically neutral, Thomson knew atoms must also have a source of positive charge to counterbalance the negative charge of the electrons.<ref>{{cite web |title=Discovery of the electron and nucleus (article) |url=https://www.khanacademy.org/science/ap-chemistry/electronic-structure-of-atoms-ap/history-of-atomic-structure-ap/a/discovery-of-the-electron-and-nucleus |website=Khan Academy |publisher=Khan Academy |access-date=9 February 2021 |language=en}}</ref><ref>{{cite web |title=4.3: The Nuclear Atom |url=https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Map%3A_Introductory_Chemistry_(Tro)/04%3A_Atoms_and_Elements/4.03%3A_The_Nuclear_Atom |website=Chemistry LibreTexts |access-date=9 February 2021 |language=en |date=4 April 2016}}</ref> |
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# Each negatively charged electron was paired with a positively charged particle that followed it everywhere within the atom. |
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# Negatively charged electrons orbited a central region of positive charge having the same magnitude as the total charge of all the electrons. |
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# The negative electrons occupied a region of space that was uniformly positively charged (often considered as a kind of "soup" or "cloud" of positive charge). |
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<blockquote>... the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification, ...<ref> |
<blockquote>... the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification, ...<ref> |
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Revision as of 16:33, 9 February 2021
The plum pudding model is one of several historical scientific models of the atom. First proposed by J. J. Thomson in 1904[1] soon after the discovery of the electron, but before the discovery of the atomic nucleus, the model tried to explain two properties of atoms then known: that electrons are negatively charged particles and that atoms have no net electric charge. The plum pudding model has electrons surrounded by a volume of positive charge, like negatively charged "plums" embedded in a positively charged "pudding".
Overview
In this model, atoms were known to consist of negatively charged electrons. Though Thomson called them "
... the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification, ...[5]
With this model, Thomson abandoned his 1890 "nebular atom" hypothesis based on the vortex atomic theory in which atoms were composed of immaterial vortices and suggested that there were similarities between the arrangement of vortices and periodic regularity found among the chemical elements.[6]: 44–45 Being an astute and practical scientist, Thomson based his atomic model on known experimental evidence of the day. His proposal of a positive volume charge reflects the nature of his scientific approach to discovery which was to propose ideas to guide future experiments.
In this model, the orbits of the electrons were stable because when an electron moved away from the centre of the positively charged sphere, it was subjected to a greater net positive inward force, because there was more positive charge inside its orbit (see Gauss's law). Electrons were free to rotate in rings which were further stabilized by interactions among the electrons, and spectroscopic measurements were meant to account for energy differences associated with different electron rings. Thomson attempted unsuccessfully to reshape his model to account for some of the major spectral lines experimentally known for several elements.[citation needed]
The plum pudding model usefully guided his student,
The colloquial nickname "plum pudding" was soon attributed to Thomson's model as the distribution of electrons within its positively charged region of space reminded many scientists of
In 1909,
Related scientific problems
The plum pudding model with a single electron was used in part by the physicist
A particularly useful mathematics problem related to the plum pudding model is the optimal distribution of equal point charges on a unit sphere, called the Thomson problem. The Thomson problem is a natural consequence of the plum pudding model in the absence of its uniform positive background charge.[9]
The classical electrostatic treatment of electrons confined to spherical quantum dots is also similar to their treatment in the plum pudding model.[10][11] In this classical problem, the quantum dot is modeled as a simple dielectric sphere (in place of a uniform, positively charged sphere as in the plum pudding model) in which free, or excess, electrons reside. The electrostatic N-electron configurations are found to be exceptionally close to solutions found in the Thomson problem with electrons residing at the same radius within the dielectric sphere. Notably, the plotted distribution of geometry-dependent energetics has been shown to bear a remarkable resemblance to the distribution of anticipated electron orbitals in natural atoms as arranged on the periodic table of elements.[11] Of great interest, solutions of the Thomson problem exhibit this corresponding energy distribution by comparing the energy of each N-electron solution with the energy of its neighbouring (N-1)-electron solution with one charge at the origin. However, when treated within a dielectric sphere model, the features of the distribution are much more pronounced and provide greater fidelity[clarification needed] with respect to electron orbital arrangements in real atoms.[12]
References
- ^ "Plum Pudding Model". Universe Today. 27 August 2009. Retrieved 19 December 2015.
- JSTOR 531468.
- ^ "Discovery of the electron and nucleus (article)". Khan Academy. Khan Academy. Retrieved 9 February 2021.
- ^ "4.3: The Nuclear Atom". Chemistry LibreTexts. 4 April 2016. Retrieved 9 February 2021.
- ^ .
- ISBN 978-0691095523.
- ^
Angelo, Joseph A. (2004). Nuclear Technology. ISBN 978-1-57356-336-9.
- ^ Salpeter, Edwin E. (1996). Lakhtakia, Akhlesh (ed.). Models and Modelers of Hydrogen. Vol. 65. World Scientific. pp. 933–934. )
- ^ Levin, Y.; Arenzon, J. J. (2003). "Why charges go to the Surface: A generalized Thomson Problem". Europhys. Lett. 63 (3): 415–418. .
- ^ Bednarek, S.; Szafran, B.; Adamowski, J. (1999). "Many-electron artificial atoms". Phys. Rev. B. 59 (20): 13036–13042. .
- ^ a b
LaFave, T., Jr. (2013). "Correspondences between the classical electrostatic Thomson problem and atomic electronic structure". J. Electrostatics. 71 (6): 1029–1035. doi:10.1016/j.elstat.2013.10.001.)
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LaFave, T., Jr. (2014). "Discrete transformations in the Thomson Problem". J. Electrostatics. 72 (1): 39–43. doi:10.1016/j.elstat.2013.11.007.)
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: CS1 maint: multiple names: authors list (link