Talk:Plum pudding model/Archive 1

Archive 1

Textbook Contradiction

This article mentions a "little known fact" that the electrons in the model were dynamic and stabilised in orbits "by the fact that when an electron moved farther from the center of the positive cloud, it felt a larger net positive inward force, because there was more material of opposite charge, inside its orbit" However, I have a textbook that states "each electron would take up a position in the jelly as far as possible from all other electrons owing to electrostatic repulsion" Can anyone verify the correct model? Textbook source - "Year 12 Senior Physics" Moyle, Allan, Millar, Molde. published 1989. pg 230 Paper.plane.pilot 19 Oct 06

Probably a case of textbook oversimplification. I'd be more inclined to trust histories of science than textbooks, which of necessity must present concepts in an idealised and simplified form. EdC 20:51, 19 October 2006 (UTC)

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Apparantly, the plum pudding model was actually thought up the the anchient greeks, or somthing like that, about 2000-3000 yeras ago. Though they didnt call it the plum pudding, they just called it a mass of positive charge with minute negetive charge to balance it out...so with this in mind, where the hell did the neutrons come from??? — Preceding unsigned comment added by 82.45.8.219 (talk) 13:23, 5 June 2006 (UTC)

The ancient Greeks did not know "positive" from "negative". These terms are from Benjamin Franklin.

Up to 1932, it was thought the nucleus of atoms heavier than hydrogen had nuclear electrons, since the nuclear mass of these atoms was larger than it should have been for the charge (as compared with hydrogen) by about double. But in 1932 the neutron was discovered as a separate particle about as heavy as the proton with no charge, so it replaced the "proton plus nuclear electron." The earlier idea wasn't such a bad model, BTW, since neutrons do decay to protons, electrons (and antineutrinos). But long before 1932 it had been realized that electrons cannot be confined in the nucleus before they are created there as betas, as this would require far too much energy for quantum mechanical reasons. Far more than is available. So the neutron was badly needed. It has no electron "inside" it. Sbharris 19:36, 5 June 2006 (UTC)

Modern models

Extended content

The final irony of the Physics is that the pudding model is always more correct than the (classical) notion of a pointlike nucleus. Indeed, the nuclei bound in a solid move around their equilibrium positions, and their positive charges are smeared over a rather wide region. Even in an isolated atom the nucleus, bound only with light electrons, turns around of atomic center of inertia, and that smears its positive charge. The positive “cloud” in an atom is described with the second atomic form-factor fnn(q) [1] which strongly depends on the atomic state |n,l,m>. This form-factor stands at the Rutherford elastic cross section, so the purely elastic “backward” scattering is suppressed by |fnn(q)|2. The higher is the initial (and the final for elastic processes) target atom state n, the stronger is suppression of the deflected “backward” projectiles. For example, in the excited Hydrogen atom with n=43 (Rydberg state), the positive cloud is of the Bohr radius. In the ground Hydrogen state the charge is smeared within 30•10-13 cm, that is certainly larger than the “proper” proton radius. In a “condensed matter” the positive cloud localization is of the atomic size. So the condensed matter structure resembles the pudding model. Apart from elastic, there are inelastic second form-factors fnn’(q). They give the amplitudes of atom exciting due to transmitting the big momentum q to the nucleus at the “backward” scattering. Ernest Rutherford, his colleagues, and the followers did not resolve the alfa-particle energies with the accuracy of 10-100 eV, so they all measured inclusive cross sections (elastic plus all energetically admitted inelastic) rather than the elastic one. The inclusive cross section, according to the quantum mechanics, coincides with the Rutherford formula [1]. This means that in calculations of the number of scattered backward projectiles one can safely use the notion of the pointlike (“free”) nucleus, but one should never think that the target atoms (or more generally – the target energy levels) do not get excited. All this is quite natural. As soon as we agree that the Rutherford formula is the inclusive result, we have to recognize that there is no ground for the pointlike nucleus notion. Piling up different events does not create an objective notion, but the crude classical one. In other words, the classical “image of pointlike free” nucleus is always the sum of quantum mechanical images of different “pale photographs” of the bound system undergoing all possible transitions in course of “observations” (scattering). Thus, the inclusive picture is literally a cinematographic illusion obtained with superposing all particular images of quite different elastic and inelastic events (frames of dσnn'(q)). By the way, this result is completely opposite to the theories of hidden variables where the “randomness” of quantum mechanics is explained with averaging a deterministic theory trajectories over some hidden parameters. In practice there is no possibility to distinguish the fast scattered projectiles with precision of about 10 – 20 or 100 eV. It is even not possible to prepare the incident beam with that energy accuracy. That is why dealing only with scattered projectiles gives inevitably the inclusive cross section. Another matter is observing recoil atoms. The excited atoms radiate. The atoms excited due to hitting electrons (described with the usual atomic form-factor Fnn'(q) under small angle scattering) radiate standard spectral lines. The target atoms excited due to hitting the nucleus (determined with fnn’(q) under large angle scattering) receive big momenta; therefore their spectral lines will be essentially shifted (Doppler effect). Registering simultaneously the scattered “backward” projectile and the shifted spectral lines permits distinguishing different inelastic processes. Thus, it is possible in principle to measure the elastic and inelastic cross sections separately. The target atoms should obviously be in a gas state of small density in order not to damp the excitations by the interatomic collisions. Vladimir Kalitvianski. 1. Attenuation of the Rutherford scattering and atom exciting by fast charged particles for large-angle scattering. Ukrainian Journal of Physics, V. 38, N 6, 1993, pp. 851-854, and Preprint of Sukhumi Institute of Physics and Technology 90-8, 1990, V. Kalitvianski, (in Russian). — Preceding unsigned comment added by 86.206.133.9 (talk) 20:44, 8 August 2006 (UTC) Vladimir, I am laboring to understand you. The gold nucleus is far heavier than the H nucleus, so charge smearing due to center of mass smearing is far smaller, especially as this is a system of many electrons in counterbalance, not one. And gold atoms vibrate, but at the speed of an alpha particle, they may as well be standing still, and that is why Rutherford's formula gives point-like results. I don't understand what "excited states" you're talking about-- nuclear excited states? The alphas never penetrate the nuclear charge in gold except for an extremely rare tunnelling event (too rare to ever see), so they never reach the nucleus to excite it. If they did, you'd get a big departure from the Rutherford formula for small impact parameters, showing you that the alphas had enough energy to actually experience inelastic scattering. But that isn't seen. That it's possible to see departures of this type due to inelastic alpha impacts with lower Z nuclei was proven by Rutherford himself, who noted departure from the elastic model at very small impact parameters when scattering alphas from hydrogen. His minimal r corresponded to about 3.5 fm, which is just about the combined radii of an alpha and a proton. This is semi-classical still. So I suppose I don't get what you're trying to say. SBHarris 21:35, 8 August 2006 (UTC) Dear Steve, Concerning excited states – it is atomic excited states, not the nucleus ones. Here I consider an atom as a bound state of a “pointlike” nucleus and the electrons. To excite atomic levels you can “hit” the electrons or the nucleus. “Backward” scattering corresponds to “hitting” the nucleus, so the motion of atomic electrons relative to the nucleus gets perturbed. (“Hitting” means, of course, the potential interaction of the fast charged projectile with the nucleus electrostatic potential.) Textbooks on atomic physics replace the nucleus coordinates with the atomic center of inertia coordinates (unnecessary and erroneous simplification), so they “hit” the atomic center of inertia. Doing so, you will never excite the atom however big is the transferred momentum. With this (unnecessary and erroneous) simplification a finny story is connected. In the thirties (1939) A. Migdal tried to calculate the probability of atom exciting with neutron. The neutron interacts only with the nucleus, but if you use the center of inertia variables (rather than the nucleus ones) you cannot excite the atom – it receives the transferred momentum as a whole. On the other hand, it is physically clear that the atom should get excited if one hits the nucleus. A. Migdal spent a lot of efforts trying to calculate this probability, and the solution clue had finally come to him in his sleep. He did manage to get the correct answer by means of considering the problem in the moving reference frame and using then the theory of sudden perturbations. In reality this probability is obtained immediately and automatically in the first Born approximation if one uses the true nucleus coordinates rather than coordinates of atomic CI in a short-range neutron-nucleus potential [1]. Here I just do not simplify the coordinates of the interacting particles. Nothing else. You are right saying that the gold nucleus is very heavy, so for the atom of gold the second elastic atomic form-factor is close to unit (do not confuse it with the nuclear form-factor discovered by Hofstadter). Yet, it is possible to “feel” it with using a heavier or a faster projectile. In addition, you can increase the atomic positive cloud size if you prepare the separate target atoms in metastable excited states (Rydberg atomic states n >> 1). But in a solid state the atomic form-factor is replaced with the “lattice” form-factor that manifests much larger nucleus delocalization. Here the nuclei are “bound” to each other rather than to the light electrons, that is understandable even for a two-atom molecule. It is also true that the projectile velocity may be much higher than the nucleus velocity in the target. The faster projectile is, the better is the first Born approximation in the quantum mechanics. And the latter gives a nucleus picture (photo) averaged over different “semi-classical” positions of the nucleus bound in the target. This is the origin of the second elastic atomic (or target) form-factor. (The first form-factor describes the negative target cloud.) The system of many electrons does not counterbalance the nucleus motion in the sense that it does not put the nucleus in the center of inertia. There is always a (symmetric or asymmetric) positive cloud, and its size is at least of order (me/mA)an where an is the target atom size. The projectile momentum after an elastic collision p’ is numerically very close to that after inelastic collision: p’=p[1-(En’ -En)/(p2/2m)]1/2 if the projectile kinetic energy p2/2m is much higher than the atomic energy differences En’ -En. So it is practically impossible to distinguish (resolve) the scattered particles on the lost energy with that precision. To detect the excitations, it is necessary to deal with the target final states rather than with the projectiles. One of the simplest ways is to use a small density gas target (with separate atoms). The Doppler shift of recoil atoms gives the quantitative description of the scattering from the bound nucleus. You may say: “Let us get rid of all electrons and other environment. Let us consider the free nucleus as a target. Then it will be pointlike.” By saying “pointlike” you mean that there is nothing in the space but the sizeless point. You approach the nucleus closer and closer, and there is still nothing in the space. Until you touch the point. What is wrong with this idea? The first strangeness is that the pointlike particles need long-distance potentials to interact. This need means nothing but some rather extended nature of charged “particles”. The second problem is the stability of charged particle systems. We need to replace the classical trajectories with the De Broglie waves in order to obtain stability. The De Broglie waves mean that the whole space participates in creating a “particle” as a wave packet. The more exact description we elaborate, the father from pointlikeness we go. Let us look at the Moon. We may describe it as a pointlike mass furnished with the Newtonian potential. In the classical mechanics its motion is potential and elastic. But we observe the Moon with help of light scattering, viz. with help of inelastic processes. The Moon is more complicated than a simple point R(t). It undergoes internal changes all the time, but we attribute its different images to one and the sole body and create the notion of the Moon. So the classical Moon is in fact the sum of all different images (inclusive picture). And in the space between the Moon and the Earth there are we, there is life. Our energy levels are much smaller than the Moon kinetic energy, so our fuss does not change much the Moon orbit, that is why we are tempted to neglect it in the theory. As I said before, in experiment we do not neglect but sum up different low energy events. An exact theory should take this fact into account. The same is valid for the atomic nucleus as well as for the other “elementary” free particles. In particular, scattering from the free nucleus is not elastic because it is always accompanied with soft (low energy) radiation. I would say that there is always a “low energy life” in the space, so the space with a pointlike nucleus is not actually empty but necessarily “filled”. The pointlike particle cannot be "alone"! Here also, only the sum of all different radiation cross sections gives the “mechanical” cross section (the Rutherford or another elastic one). As soon as it is so, is it correct to insist on pointlikeness as on the fundamental feature of anything? I do not think so. Sincerely, Vladimir Kalitvianski. — Preceding unsigned comment added by 86.206.133.9 (talk) 10:41, 9 August 2006 (UTC)

Tone of article

I find the tone of the article to read like a "did you know" rather than an encyclopedic article. Tristandeboer 21:01, 9 April 2007 (UTC)

It is sometimes difficult to discover what the writer is trying to say because the language used is a little obscure. Take the introductory sentence for instance: "The plum pudding model, also known as the blueberry muffin model, of the atom by J. J. Thomson, who discovered the electron in 1897, was proposed in 1904 before the discovery of the atomic nucleus in order to add the electron to the atomic model". I am uninformed about the topic, but perhaps it should rather read as follows: "The plum pudding model was a model of the atom that incorporated the electron in the model of the atom, and was proposed by J.J. Thomson in 1904. Thompson discovered the electron in 1897. The plum pudding model was abandoned after discovery of the atomic nucleus. The plum pudding model of the atom was also known as the "Blueberry Muffin" model of the atom.— Preceding unsigned comment added by Obsidionite (talk) 11:41, 25 August 2014 (UTC)

Edited. Please take a look! - Ttwaring (talk) 19:34, 25 August 2014 (UTC)

headings!

I think this article needs a little extra detail and some headings to make it clearer. (Bobbyno.1 (talk) 06:36, 13 February 2012 (UTC))

Chem

What is a plum pudding defi 2409:4053:19C:F1B4:655A:6876:96D5:53CF (talk) 15:11, 24 August 2022 (UTC)

Please try asking a more detailed question at the reference desk. This page is for discussing improvements to the article. - Ttwaring (talk) 15:39, 24 August 2022 (UTC)

Wiki Education assignment: SSC199 TY4

This article was the subject of a Wiki Education Foundation-supported course assignment, between 8 November 2022 and 16 December 2022. Further details are available on the course page. Student editor(s): 0JOTARO (article contribs). Peer reviewers: Walti13.

— Assignment last updated by Omgmylife (talk) 02:27, 4 December 2022 (UTC)

Bibliography Hon, G., & Goldstein, B. R. (2013). J. J. Thomson’s plum-pudding atomic model: The making of a scientific myth. ANNALEN DER PHYSIK, 525(8-9), A129–A133.[1]

  Contains a summary of everything
  https://search.lib.buffalo.edu/discovery/fulldisplay?context=PC&vid=01SUNY_BUF:everything&search_scope=UBSUNY&tab=EverythingUBSUNY&docid=cdi_webofscience_primary_000327819400002CitationCount

J. J. Thomson, Phil. Mag. 7, 237 (1904)[2]

  About the aim of achieving chemical stable and electrically neutral
  https://www.tandfonline.com/doi/abs/10.1080/14786440409463107

J. J. Thomson, Phil. Mag. 48, 547 (1899)[3]

  Original statement about the structure of the atom | His lack of calculations is also mentioned in the initial model
  https://www.tandfonline.com/doi/abs/10.1080/14786449908621447

J. J. Thomson, Electricity and matter (Yale University Press, New Haven, 1904), p. 92.[4]

  Radio-activity comment
  https://catalog.hathitrust.org/Record/005758099

J. J. Thomson, The corpuscular theory of matter (Archibald Constable, London, 1907)[5]

  Stability and unity of atomic phenomenon, both electrical and chemical | original statement about how chemical properties come into effect | positive electricity
  https://www.nature.com/articles/077505a0

E. Rutherford, Discussion of the structure of atoms and molecules, in Report of the eighty-fourth meeting of the British Association, Australia, July 28 – August 31, 1914 (John Murray, London, 1915), p. 293.[6]

  Rutherford's take on the atom structure after his own experiments | respect for thomson
  https://www.chemteam.info/Chem-History/Rutherford-1914.html  — Preceding unsigned comment added by 0JOTARO (talk • contribs) 15:55, 21 November 2022 (UTC) 

Example of damaging false and misleading information

"Obsolete theories in physics" -- English words have meaning

A quick review of the items listed on the Wikipedia Category page of "Obsolete theories in physics," one finds more scientific models, concepts, and ideas than actual theories. These words have specific meaning. As scientific terms, those meanings are both unique and well-defined.

In this particular instance, a scientific model is not a theory, and the false categorization of this page under "obsolete theories in physics" is disingenuous, misleading and damaging to Wikipedia as an "encyclopedia" (i.e. a "reference work...providing summaries of knowledge".

1. The plum pudding model is not a theory.

2. The plum pudding model is not an obsolete model.

3. The plum pudding model is not exclusively used today in physics.

4. The plum pudding model (1904) is in fact used today in many forms, and its publication history has accelerated since at least the 1980s.

To keep this false categorization in place on a commonly used platform of scientific information by everyday people, is an example of intentional disinformation.

Looking through the edits history, the last two contributors to reinstate the false categorization of this page had these remarks to substantiate their edits:

"The defining term here is obsolete physical thing, whether a theory, model or law" -StarryGrandma "it definitely is obsolete" - Headbomb

As I noted in my corrective edit, theories, models and scientific laws are not physical things. They are ideas, abstractions, math. The category label says nothing of obsolete physical things. And to merely state that something is obsolete as reason for an edit is disingenuous and intentionally misleading. A colleague had similarly removed this categorization some time ago. As a source widely cited by everyday users, Wikipedia is not a place for false information.

Words have meaning. Incorrectly used and placed on a platform such as Wikipedia only contributes to a growing culture of disinformation that damages the integrity of the online community. Wikipedia is a platform for science communicators. if science communicators place false information here, it leads to confusion and damages the integrity of scientific knowledge. We have more than enough growing problems with conspiracy theories, and other pseudoscience gibberish in the real world to contend with that even "little" things like this can have significant consequences.

Let's look at some definitions relevant to this page and its incorrect categorization. (In fact, most items on the category page shouldn't be listed there)

Definition obsolete | no longer produced or used; out of date.

The plum pudding model is the direct orgin of the Thomson problem, which is a benchmark computational problem for every reputable electromagnetics simulation package/app today. It is certainly used today and not out of date. The plum pudding model is definitely not obsolete.

Definition: theory | a set of principles on which the practice of an activity is based.

The Thomson problem is premised on the set of principles of the plum pudidng model and is practiced today. In fact, most literature on the subject has been produced from the mid 1980s through today with applications including golf ball design, geodesic dome design, fullerenes modeling, spherical virus modeling, global weather modeling, and atomic phenomena. The plum pudding model doesn't fit the definition of a theory.

Definition Italicmodel (science) | a physical and/or mathematical and/or conceptual representation of a system of ideas, events or processes

The plum pudding model was proposed as a conceptual representation of atomic structure and a framework in which the periodic table of elements could be better understood in the early 20th century. Thomson's own related later work in the 1920s, alongside the work of chemists Lewis and Langmuir for example, led to many foundational principles in chemistry including the octet rule and covalent bonding. These principles are used today. As a model, the plum pudding model is certainly not obsolete as it is the premise of numerous fundamental principles in physics, chemistry and biology -- not just physics.

This page should not be categorized in "obsolete theories in physics" ...and the list on the category page should be reviewed with an eye toward scientific and informational integrity.

. TJ LaFave (talk) 21:05, 8 February 2023 (UTC)

Headbomb has been edit warring [1] [2] to keep this uncited category. He's argued elsewhere that this categorization is patently obvious, but the burden is on him to provide reliable sources.      — Freoh 12:54, 9 February 2023 (UTC)

It is cited. See Refs 24, 25 amongst others. And quite frankly, if you don't know that the plum pudding model is obsolete, you have no business editing this article. Headbomb {t · c · p · b} 13:23, 9 February 2023 (UTC)

It's as obsolete as a model of the atom can get. It has been outdated since the discovery of the nucleus. It has been further outdated since the discovery of quantum mechanics. The Thomson problem is a question that arose from it and has been studied for other reasons, but that doesn't make the plum pudding model anything other than an obsolete model of the atom. XOR'easter (talk) 14:17, 9 February 2023 (UTC)

For analogy: somebody figured out how to draw Homer Simpson with epicycles, but epicycles are still an obsolete way of understanding the solar system. XOR'easter (talk) 14:20, 9 February 2023 (UTC)

The analogy to epicycles is without merit here even with an assumption that my intent is to use the Thomson problem as a stand-in for the plum pudding model.

Models ≠ theories. Scientific and grammatical fact. The category does not apply here. Categories about chickens do not apply to oranges. 2 + 2 ≠ 5. Certainly not if we're being serious, professional, or sane. TJ LaFave (talk) 21:09, 24 March 2023 (UTC)

I'm a little bemused by the intensity of this challenge. Though the article may be a bit inaccurate in describing Thomson's corpuscular theory of matter, challenging the category makes no sense. —Quondum 23:09, 9 February 2023 (UTC)

@Tjlafave, you appear to be the author of the paper "Correspondences between the classical electrostatic Thomson problem and atomic electronic structure". By categorizing this atomic model as obsolete we are not saying the Thomson problem is obsolete, or that papers on it are not valuable. StarryGrandma (talk) 19:20, 13 February 2023 (UTC)

This isn't about whether or not the Thomson problem is obsolete nor whether papers about it are of any value.

In as plain English as possible, the "plum pudding model" is not a "scientific theory." Categorizing the "plum pudding model" as a "theory" is scientifically and grammatically incorrect. Further categorizing the "plum pudding model" as "obsolete" is both disingenuous and scientifically incorrect for a variety of reasons I gave earlier and many more that have impacts in many branches of science.

Ipso facto, by multiple metrics, categorizing the Wikipedia page on the "plum pudding model" as an "obsolete theory(ies) in physics" is a error. Continuing to reinstate that error is intentional disinformation.

2+2 does not equal 5. Stating this on a mathematics page would be intentional disinformation.

At least half of the linked pages from the category page in question are errors. TJ LaFave (talk) 20:54, 24 March 2023 (UTC)

Tjlafave, it seems that there is widespread disagreement over the precise criteria for inclusion in Category:Obsolete scientific theories. This was also an issue at Talk:Rayleigh–Jeans law § Not obsolete physics. I do not have strong opinions about what the inclusion criteria should be, but I think that Category:Obsolete scientific theories should document them clearly and precisely. It would probably make sense for you to open an RfC at Category talk:Obsolete scientific theories, and I could help you with that process if you are interested.  — Freoh 02:01, 26 March 2023 (UTC)

"the "plum pudding model" is not a "scientific theory."

Not anymore no. At the time, however, it was so. Now it's obsolete, and no one uses it to describe the atom anymore. Headbomb {t · c · p · b} 01:57, 6 April 2023 (UTC)

I am also surprised at the heat of the initial query in this thread. I think it is misplaced. The plum pudding model is clearly a scientific theory, and it is clearly obsolete. I say these things with at least some authority, as I am a retired professor of history of science who specialized over my 40+ year career in the close study of theories in the physical sciences of the 19th and 20th centuries, particularly atomic theory. The definitions given at the top of the thread are deficient. Throughout the history of science, models can definitely fulfill the definition of theories. In fact, the definition given above of a model can also serve as an excellent definition of a theory: "a physical and/or mathematical and/or conceptual representation of a system of ideas, events or processes"; we speak (for instance) of the geocentric or heliocentric model of the solar system. The plum pudding model (his theory of the composition of the atom) died with advent the Rutherford-Bohr nuclear atom, as Thomson well recognized. "Damaging"? "False"? "Misleading"? No, none of these.Ajrocke (talk) 18:17, 30 April 2024 (UTC)

Overview is too long and detailed.

The Overview is too dense. I'm not even sure why it exists. Seems like what we need is "Background". The intro should be the overview. Johnjbarton (talk) 03:00, 27 June 2024 (UTC)

Ok I moved content out of Overview, and deleted some of it. In its place I added a Background section with four ingredients essential for the Thomson story: atomic model, electrons, radiation, and spectral lines. Thomson uses electrons to build a model of the atom, radiation to probe matter in support of his model, but ultimately fails to describe spectral lines. Johnjbarton (talk) 18:48, 27 June 2024 (UTC)

Need a section on the experimental evidence.

Thomson and his colleague Crowther published work on the scattering of beta particles by metal foils that they used to support Thomson's model. This work should be discussed. Johnjbarton (talk) 03:09, 27 June 2024 (UTC)

Development

Unfortunately at least some of content of the Development section is wrong, and now I suspect it all. It appears to be a synopsis of self-selected contributions of Thomson by date, created by reading the original papers. It's a good example of why Wikipedia prefers secondary sources.

For example the 1905 lecture was an overview of previous work, esp. a 1903 paper where the magnetic analogy was introduced based on previous work by Alfred Marshall Mayer. Johnjbarton (talk) 21:48, 27 June 2024 (UTC)

In my experience working on many history projects on Wikipedia, secondary sources are often unreliable. They often present a distorted summarization of what came before. That's why I use both. Kurzon (talk) 22:04, 27 June 2024 (UTC)

Well I agree that many pages use web sites as if they were secondary sources or sensationalized pop-science articles that aren't historical analysis. Johnjbarton (talk) 00:50, 28 June 2024 (UTC)

Also secondary sources might contradict each other and we end up having to pick and choose and interpret anyway . Kurzon (talk) 22:17, 27 June 2024 (UTC)

Proposal for new organization of Development section.

Currently the Development section has chronological year-named subsections corresponding to some of Thomson publications or lectures. Several secondary references discuss this work as having two phases, one culminating in Thomson's 1904 paper and related lectures and a second phase triggered by his discovery that the number of electrons per atom is similar to the atomic weight ratio to hydrogen in 1906. Here is what A. Pais writes in Inward Bound:

• The period 1897-1913 consists of two distinct parts. In the first, it was believed that the number of electrons in the atom is large. In the second, it was realized that this number is of the order of the atomic number. This change was wrought by Thomson, in 1906.

I propose an organization like:

• Development (or Models?)
  • Polyelectron atomic model
    • Magnet analog, mechanical stability, comparison to periodic chart and chemistry.
  • Revised model
    • Discovery of the number of electrons per atom, consequences for the model.
  • Beta scattering theory and experiment.
    • First efforts to directly test atomic model. Initial success.

Johnjbarton (talk) 16:23, 29 June 2024 (UTC)

Eventually maybe. In writing history a good approach is to begin with a chronological approach, because timing is everything in history. Then as the information matures, it could perhaps be reorganized into something else. First, add the stuff you want to add with the chronological system. Kurzon (talk) 17:03, 29 June 2024 (UTC)

Removing incorrect reference.

The reference

• Alviar-Agnew, Marissa; Agnew, Henry (4 April 2016). "4.3: The Nuclear Atom". Introductory Chemistry. LibreTexts. Retrieved 9 February 2021.

is very short. It claims

• "The electron was discovered by J. J. Thomson in 1897. The existence of protons was also known, as was the fact that atoms were neutral in charge. Since the intact atom had no net charge and the electron and proton had opposite charges, the next step after the discovery of subatomic particles was to figure out how these particles were arranged in the atom."

The proton was not properly identified until at least 1917. Thomson's models had no protons. The reference appears in support of "as was the fact that atoms were neutral in charge". However this is not needed in the article because the reason Thomson needed positive charge was stability, not neutrality. Johnjbarton (talk) 23:23, 30 June 2024 (UTC)

Also the ref says:

• "In Thomson's plum pudding model of the atom, the electrons were embedded in a uniform sphere of positive charge like blueberries stuck into a muffin."

which is complete baloney. Johnjbarton (talk) 23:25, 30 June 2024 (UTC)

J. Arnold Crowther

One of the main protagonists in the atomic theory of 1905-1910 is James Arnold Crowther. Given so many dubiously notable biographies on Wikipedia I was surprised to discover nothing about him here. In addition to his publications on beta scattering, consider published books:

• Crowther, James Arnold. Ions, electrons, and ionizing radiations. Longmans, Green, 1924.
  • "Many have owed their first acquainance with modern physics to this excellent intermediate text, which reached its eigth and final edition in 1949, the year before Crowther's death." Heilbron, 1968, footnote on page 296.
• Crowther, James Arnold. A manual of Physics. H. Frowde, 1919.
• Crowther, James Arnold. Molecular Physics. J. & A. Churchill, 1923.
• Crowther, James Arnold. The life and discoveries of Michael Faraday. Society for promoting Christian knowledge, 1920.

His obitutary:

• Whiddington, R. "Prof. JA Crowther." Nature 165.4202 (1950): 750-751.

Johnjbarton (talk) 18:02, 6 July 2024 (UTC)

I created a page for James Arnold Crowther.  Done Johnjbarton (talk) 16:06, 12 July 2024 (UTC)

Thomson problem

Has anyone ever done a computer simulation of a Thomson atom with 100 or so atoms, arranged in shells like Thomson imagined? The Thomson problem solutions I found online constrain the electrons to the surface of the sphere. Kurzon (talk) 16:45, 11 July 2024 (UTC)

Thomson's 1906 paper discusses analytic stability of his shells in detail. Johnjbarton (talk) 16:59, 11 July 2024 (UTC)

I am looking for a diagram. Kurzon (talk) 08:44, 12 July 2024 (UTC)

My diagram

@Ajrocke and Johnjbarton: I drew this diagram of the plum pudding model based on a 1905 diagram by JJ Thomson. The electrons are arranged in a pentagonal dipyramid, equidistant from the center. Is this a good diagram or misleading? Kurzon (talk) 19:15, 28 April 2024 (UTC)

As a re-drawing of a historical diagram I think it is fine. I will tweak the caption. Johnjbarton (talk) 15:24, 29 April 2024 (UTC)

Should all the electrons be the same distance from the center of the sphere? I wonder if the peaks of the pyramids should be a different distance. Kurzon (talk) 08:48, 12 July 2024 (UTC)

The diagram looks like the ones in Thomson's paper. Johnjbarton (talk) 00:37, 13 July 2024 (UTC)

Have you seen one that shows multi-shell electrons? I have heard of the "Thomson problem" in mathematics but all the diagrams I find constrain the electrons to the surface of the sphere. Kurzon (talk) 06:52, 13 July 2024 (UTC)

I have not see such a diagram. Thomson's analysis of the multi-ring case was very limited. Above 6 electrons he finds that stability requires adding electrons in the center of the atom. Above 9 electrons the number of electrons in the center increase until at 15 he needs 15 in the center. (Recall that as more electrons are added the positive sphere also increases in strength). The electrons in the center then repel, leading to an inner ring. By this analysis he gets multi-rings. But he cannot do stability calculations on multiple rings, he's just guessing at this point.

Bohr later said the equivalent of "he's making stuff up". Pais notes that Thomson generally considered physical models to be stories useful for generating ideas rather than the basis of quantitative analysis. (I can something about this to the article if you think it useful). And note that the great success of Bohr's later shell model follows the idea of rings of special stability. Johnjbarton (talk) 16:25, 13 July 2024 (UTC)

Nobody has tried a computer simulation? Kurzon (talk) 18:20, 13 July 2024 (UTC)

Perhaps if we expand the section on the Thomson problem one will come up. Johnjbarton (talk) 02:25, 14 July 2024 (UTC)

It looks fine to me.Ajrocke (talk) 17:56, 30 April 2024 (UTC)

Dalton's was the first

@Johnjbarton: I don't want to be pedantic, but Dalton's model of the atom was the first. It had atomic weights, which is not much but something. Kurzon (talk) 21:44, 13 July 2024 (UTC)

I have previously discussed this issue under Lead_sentence_is_inappropriate. Johnjbarton (talk) 03:48, 14 July 2024 (UTC)

You're good at physics, not so much prose. Kurzon (talk) 13:49, 22 July 2024 (UTC)

How about this as the first sentence:

• The plum pudding model was the first scientific model of the atom with internal structure.

This simple declarative sentence notes the historical significance of the topic. Dalton's model did not have internal structure. Johnjbarton (talk) 18:01, 22 July 2024 (UTC)

How is this image incorrectly labelled?

Explain. Kurzon (talk) 18:50, 25 July 2024 (UTC)

The image that was added to the page did not have the electron labeled. Johnjbarton (talk) 20:42, 25 July 2024 (UTC)

Well once again there is no edit summary but this time the image is complete. Johnjbarton (talk) 21:05, 25 July 2024 (UTC)

Why the Thomson model was(n't) wrong

We now have a section entitled "Why the Thomson model was wrong". This kind title gives an inaccurate sense of how scientific models work. I think you will almost never see "wrong" in print for a science model. Every single scientific model is "wrong" in some way: what's the point? Model are "useful" or "not useful" according to successful predictions in specific circumstances. Until the Geiger-Marsden experiment and Rutherford's explanation, Thomson model was useful. Then new circumstances: it could not predict the large angle scattering.

I think Thomson's scattering model should be presented straight-up, then contrasted with the new results of Rutherford. As it is I don't understand what part of the section is representing Thomson scattering and what part is tearing it down. Johnjbarton (talk) 23:52, 11 August 2024 (UTC)

I think you're splitting hairs here. Kurzon (talk) 07:51, 12 August 2024 (UTC)

No, it's an aspect of the philosophy of science. You might like to read about how "all models are wrong":

• Box, George EP. "Science and statistics." Journal of the American Statistical Association 71.356 (1976): 791-799. https://www.tandfonline.com/doi/pdf/10.1080/01621459.1976.10480949?casa_token=lTCK50__6ckAAAAA:2VcLVFFpsex1vPJy6_Cd94z96xKpRUAGrVbIG8rtqhy3cEK1sr4t9S7TNgG-fVszjiv9MXSD5GBYDQ

Johnjbarton (talk) 15:43, 13 August 2024 (UTC)

So you want me to use rough approximations in the math but you're going to split hairs when it comes to prose? Kurzon (talk) 17:44, 13 August 2024 (UTC)

No. I want you to use appropriate approximations and appropriate prose according to physics in a physics article. These are connected. Using a number like 0.0186 in a physics context is not the same as 0.02. The value 0.02 is not a "rough approximation", it is additional information. It tells the reader that "we are seeking to understand a complex phenomenon so we will focus on the general character." On the other hand 0.0186 means we have confidence that our model will reproduce experiments to 4 significant figures. But "all models are wrong". The 0.0186 is mice when lions abound. We have no experimental data with 4 significant figures and not a prayer that our textbook exercise will match even if we did. The 0.0186 number is incorrect. If you wrote that on a physics exam its points off. Johnjbarton (talk) 18:49, 13 August 2024 (UTC)

Where did Thomson get this?

@Johnjbarton, Headbomb, and Materialscientist: In a 1910 paper, Thomson said that this equation gives the average deflection angle for a single collision with the positive sphere. Thomson merely says that "it is easy to show" this is true, he didn't explain it. Any ideas on how he got this equation?

$${\bar {\theta }}_{1}={\frac {\pi }{4}}\cdot {\frac {kq_{a}q_{g}}{mv^{2}}}\cdot {\frac {1}{r}}\approx 0.00013{\text{ radians or 0.007 degrees}}$$

Kurzon (talk) 11:33, 13 August 2024 (UTC)

It'd help a lot if you included the citation to that paper. Headbomb {t · c · p · b} 11:44, 13 August 2024 (UTC)

J. J. Thomson (1910). "On the Scattering of rapidly moving Electrified Particles". Proceedings of the Cambridge Philosophical Society. 15: 465–471. Kurzon (talk) 12:03, 13 August 2024 (UTC)

@Kurzon You deleted the content that explains this formula and references two places that discuss it. Johnjbarton (talk) 15:22, 13 August 2024 (UTC)

Heilbron has an explanation for it and it's nothing like what we had. Kurzon (talk) 21:44, 13 August 2024 (UTC)

Heilborn reproduces Thomson's derivation based on Rutherford's notes. See Heilbron Appendix A, Fig 19. This is beta scattering from positive sphere and uses an impulse approximation averaged over a line across the sphere.

Beiser is the version you deleted, page 106. It uses an impulse approximation at the rim of a positive sphere for alpha particle scattering.

Per the title of Thomson's 1910 paper, beta/alpha/positive/negative it's all Coulomb scattering. The differences show up in the momentum change (and in many details other than the Coulomb scattering).

The difference between the two models of scattering are insignificant in the sense I discussed above. Johnjbarton (talk) 22:18, 13 August 2024 (UTC)

Heilbron gives us this integral in his essay. It doesn't make sense to me.

$\varphi _{2}=(1/\pi a^{2})\int _{0}^{a}(ne^{2}/ma^{3}v^{2})(2p{\sqrt {a^{2}-p^{2}}})(2\pi pdp)=(\pi /4)(ne^{2}/mv^{2}a)$

What confuses me is how pi survives the integration. As, doesn't

$(1/\pi a^{2})\int _{0}^{a}(ne^{2}/ma^{3}v^{2})(2p{\sqrt {a^{2}-p^{2}}})(2\pi pdp)=(1/\pi a^{2})2\pi \int _{0}^{a}(ne^{2}/ma^{3}v^{2})(2p{\sqrt {a^{2}-p^{2}}})(pdp)=(1/a^{2})2\int _{0}^{a}(ne^{2}/ma^{3}v^{2})(2p{\sqrt {a^{2}-p^{2}}})(pdp)$?

Kurzon (talk) 11:51, 16 August 2024 (UTC)

Heilbron says he is averaging $pL$ over the "disk" which I guess has to be a sphere. The average value of $pL$ over of the sphere gives the internal $2*2\pi$ but I don't know where the extra $p$ comes from.

Since he ends up with Thomson's formula, I guess the averaging formula is mis-typeset or something like that.

I thought this approach was too complicated which is why I used Beiser. Johnjbarton (talk) 19:15, 16 August 2024 (UTC)

Well what about historical accuracy? Kurzon (talk) 19:21, 16 August 2024 (UTC)

I gave a try, see what you think. Johnjbarton (talk) 22:39, 16 August 2024 (UTC)

Nevermind, I used this tool: https://www.symbolab.com/solver/definite-integral-calculator/

Sweet crackers, if I had this when I was a teenager, high school would have been so much sweeter. Kurzon (talk) 06:36, 18 August 2024 (UTC)

Scattering section incorrect.

• Rutherford did not use Thomson's scattering model.
• The formulas partly consider multiple scattering when the claim is single.
• Thomson did not consider Geiger/Marsden results, obviously.
• Thomson never considered large angle scattering in his model.
• the section is based on Thomson's 1910 paper, long after he determined the more correct number of electrons

Johnjbarton (talk) 01:18, 17 August 2024 (UTC)

I think this section is attempting to do too much. It mixes Thomson/Rutherford theory/experiment and jumbles up the timeline. A better presentation would just focus on Thomson's scattering model as promised and mention Crowther's experimental confirmation. Then, in the next subsection, we can summarize Rutherford scattering experiment and the consequences, already well covered in that article. Johnjbarton (talk) 03:16, 17 August 2024 (UTC)

This revision of the article corrects all of the above issues. However @Kurzon reverted it with the edit summary "this is better". Johnjbarton (talk) 15:15, 19 August 2024 (UTC)

Yeah maybe yours is better. I've decided to adapt Heilbron's explanation of how Thomson produced the equation for positive sphere scattering, tell me what you think. Kurzon (talk) 15:56, 19 August 2024 (UTC)

Adding Crowther's experimental results.

The section on the 1910 paper would be better if Crowther's results were summarized. That would help clarify that Thomson's model seemed to work until the Geiger-Marsden experiment results became known. Johnjbarton (talk) 00:00, 25 August 2024 (UTC)

I added one paragraph about one set of Crowther experiments. Johnjbarton (talk) 00:33, 25 August 2024 (UTC)