Free download program migo land hack program. Estudos sobre a natureza elétrica da matéria do final do século XIX iniciaram uma lenta mudança na concepção de átomo. Uma vez que o modelo de Dalton não previa nenhum tipo de atividade elétrica, cientistas que desenvolviam trabalhos com a eletricidade começaram a questionar-se a respeito da validade deste modelo.

Em 1903, Joseph John Thomson (1856-1940) propôs uma explicação satisfatória ao fenômeno elétrico da matéria. Em seus estudos, Thomson adaptou a ampola de Crookes (ampola de raios catódicos), visando testar a natureza elétrica destes raios. Detectou então que as partículas que eram geradas no cátodo (daí o nome raio catódico) eram desviadas pelo eletrodo positivo e independiam das outras variáveis do experimento (gás que preenchia a ampola; o metal que compunha o cátodo ou o ânodo; o metal que compunha os eletrodos).

Questo modello atomico fu proposto dallo scienziato inglese Joseph John 'J.J.' Thomson nel 1904, con lo scopo di spiegare la composizione degli atomi sulla base delle nozioni di cui avevamo conoscenza a quel punto. Thomson atomic model, earliest theoretical description of the inner structure of atoms, proposed about 1900 by William Thomson (Lord Kelvin) and strongly supported by Sir Joseph John Thomson, who had discovered (1897) the electron, a negatively charged part of every atom.

Thomson então determinou o desvio que o raio catódico sofrera pelo campo magnético positivo do eletrodo, chegando à conclusão de que os raios catódicos eram formados por feixes de partículas idênticas, de carga negativa, de massa extremamente pequena e de menor carga elétrica. Conforme citado no parágrafo anterior, devido à característica do raio catódico ser desviado independentemente das condições, Thomson afirmou ser esta partícula negativa inerente a todos os átomos e denominou-a elétron.

Este é um resumo das bases teóricas que permitiram a Thomson propor o seu modelo atômico. Utilizando-se de preceitos do modelo de Dalton (massas dos átomos), Thomson incluiu o resultado teórico de suas observações ao modelo vigente, sugerindo assim a explicação que ficou conhecida o modelo atômico de Thomson.

Thomson admitia que o átomo fosse composto por cargas positivas e negativas (ambas foram detectadas em suas pesquisas). Segundo seu postulado, a esfera maciça possuiria carga positiva. A carga negativa seria representada por incrustações nesta esfera positiva. Na imagem a seguir temos uma possível representação do modelo de Thomson, que ficara conhecido também como modelo “pudim de passas”.

Representação sem escala e em cores fantasia do modelo atômico de Thomson.

Dr fone wondershare iphone crack. A possibilidade de explicar o comportamento elétrico das substâncias químicas, como a formação de compostos iônicos quando se solubilizam sais e a condutibilidade proveniente desta dissolução. O comportamento de metais frente à condução elétrica também é exemplo de como este modelo explica condições na natureza, que o modelo de Dalton não era capaz de explicar.

Para Thomson, os elétrons incrustados na esfera positiva (próton) deveriam estar em quantidade suficiente para anular as cargas positivas, tornando-se um corpo eletricamente neutro. A formação dos íons se daria pelo desequilíbrio nesta relação, onde o papel dos elétrons dispersos na esfera positiva seria vital: seriam eles que sofreriam aumento ou diminuição em seus números. Logo, para que um átomo apresentasse comportamento iônico, ela deveria apresentar excesso ou falta de cargas negativas.

Átomos que perdessem um elétron ficariam positivamente carregados, justamente por existir uma carga positiva a mais em relação ao número de elétrons (prótons > elétrons), tornando-se um íon positivo ou cátion. O contrário também aconteceria, segundo Thomson, pois possuindo um elétron a mais o átomo terminaria por carregar-se negativamente (próton < elétron), tornando-se um íon negativo ou ânion.

Com o advento da radioatividade, cientistas questionaram características do modelo atômico de Thomson frente a novos fenômenos, e a ciência dos modelos atômicos deu mais um avanço na história, com o modelo de Rutherford.

Referências:

LISBOA, J. C. F. Química, 1º ano: ensino médio. 1ª Ed. – São Paulo: Edições SM, 2010. (coleção Ser protagonista). p. 113 – 115.

FELTRE, R. Química Geral – 5ª Ed. – São Paulo: Moderna, 2000. p.84 – 87.

FELTRE, R; YOSHINAGA, S. Atomística – 1ª Ed. – São Paulo: Moderna, 1970. p. 25 – 34.

Texto originalmente publicado em https://www.infoescola.com/quimica/modelo-atomico-de-thomson/

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[edit]

In this model, atoms were known to consist of negatively charged sub-atomic particles. Though Thomson called them 'corpuscles', they were more commonly called 'electrons' which G. J. Stoney proposed as the 'fundamental unit quantity of electricity' in 1891.^[2] At the time, atoms were known to have no net electric charge. Thomson knew that atoms must have a source of positive charge to counterbalance the negative charge of the electrons.^[3][4]Thomson published his proposed model in the March 1904 edition of the Philosophical Magazine, the leading British science journal of the day. In Thomson's view:

Thomson Atomo Divisivel

.. 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.

Thomson Atomic Experiment

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, Ernest Rutherford, to devise experiments to further explore the composition of atoms. Also, Thomson's model (along with a similar Saturnian ring model for atomic electrons put forward in 1904 by Nagaoka after James Clerk Maxwell's model of Saturn's rings) were useful predecessors of the more correct solar-system-like Bohr model of the atom.

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 raisins, then called 'plums,' in the common English dessert, plum pudding.

In 1909, Hans Geiger and Ernest Marsden conducted experiments with thin sheets of gold. Their professor, Ernest Rutherford, expected to find results consistent with Thomson's atomic model. It was not until 1911 that Rutherford correctly interpreted the experiment's results^[7][8] which implied the presence of a very small nucleus of positive charge at the center of gold atoms. This led to the development of the Rutherford model of the atom. Immediately after Rutherford published his results, Antonius Van den Broek made the intuitive proposal that the atomic number of an atom is the total number of units of charge present in its nucleus. Henry Moseley's 1913 experiments (see Moseley's law) provided the necessary evidence to support Van den Broek's proposal. The effective nuclear charge was found to be consistent with the atomic number (Moseley found only one unit of charge difference). This work culminated in the solar-system-like (but quantum-limited) Bohr model of the atom in the same year, in which a nucleus containing an atomic number of positive charges is surrounded by an equal number of electrons in orbital shells. As Thomson's model guided Rutherford's experiments, Bohr's model guided Moseley's research.

Related scientific problems[edit]

The plum pudding model with a single electron was used in part by the physicist Arthur Erich Haas in 1910 to estimate the numerical value of Planck's constant and the Bohr radius of hydrogen atoms. Haas' work estimated these values to within an order of magnitude and preceded the work of Niels Bohr by three years. Of note, the Bohr model itself provides reasonable predictions only for atomic and ionic systems with just one effective electron.

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[edit]

Thomson Atomic Theory Date

1. ^'Plum Pudding Model'. Universe Today. 27 August 2009. Retrieved 19 December 2015.
2. ^O'Hara, J. G. (Mar 1975). 'George Johnstone Stoney, F.R.S., and the Concept of the Electron'. Notes and Records of the Royal Society of London. Royal Society. 29 (2): 265–276. doi:10.1098/rsnr.1975.0018. JSTOR531468.
3. ^'Discovery of the electron and nucleus (article)'. Khan Academy. Khan Academy. Retrieved 9 February 2021.
4. ^'4.3: The Nuclear Atom'. Chemistry LibreTexts. 4 April 2016. Retrieved 9 February 2021.
5. ^Thomson, J. J. (March 1904). 'On the Structure of the Atom: an Investigation of the Stability and Periods of Oscillation of a number of Corpuscles arranged at equal intervals around the Circumference of a Circle; with Application of the Results to the Theory of Atomic Structure'(PDF). Philosophical Magazine. Sixth. 7 (39): 237–265. doi:10.1080/14786440409463107.
6. ^Kragh, Helge (2002). Quantum Generations: A History of Physics in the Twentieth Century (Reprint ed.). Princeton University Press. ISBN978-0691095523.
7. ^Angelo, Joseph A. (2004). Nuclear Technology. Greenwood Publishing. p. 110. ISBN978-1-57356-336-9.
8. ^Salpeter, Edwin E. (1996). Lakhtakia, Akhlesh (ed.). Models and Modelers of Hydrogen. American Journal of Physics. 65. World Scientific. pp. 933–934. Bibcode:1997AmJPh.65.933L. doi:10.1119/1.18691. ISBN978-981-02-2302-1.
9. ^Levin, Y.; Arenzon, J. J. (2003). 'Why charges go to the Surface: A generalized Thomson Problem'. Europhys. Lett. 63 (3): 415–418. arXiv:cond-mat/0302524. Bibcode:2003EL...63.415L. doi:10.1209/epl/i2003-00546-1.
10. ^Bednarek, S.; Szafran, B.; Adamowski, J. (1999). 'Many-electron artificial atoms'. Phys. Rev. B. 59 (20): 13036–13042. Bibcode:1999PhRvB.5913036B. doi:10.1103/PhysRevB.59.13036.
11. ^ ^abLaFave, T., Jr. (2013). 'Correspondences between the classical electrostatic Thomson problem and atomic electronic structure'. J. Electrostatics. 71 (6): 1029–1035. arXiv:1403.2591. doi:10.1016/j.elstat.2013.10.001.
12. ^LaFave, T., Jr. (2014). 'Discrete transformations in the Thomson Problem'. J. Electrostatics. 72 (1): 39–43. arXiv:1403.2592. doi:10.1016/j.elstat.2013.11.007.

Thomson Automotive