Joseph John Thomson, better known as J. J. Thomson, was a British physicist who first theorized and offered experimental evidence that the atom is a divisible entity rather than the basic unit of matter, as was widely believed at the time. A series of experiments with cathode rays he carried out near the end of the 19th century led to his discovery of the electron, a negatively charged atomic particle with very little mass. Thomson received the Nobel Prize in Physics in 1906 for his work exploring the electrical conductivity of various gases.

The son of a bookseller, Thomson was born on December 18, 1856, in Cheetham Hill, located just north of Manchester, England. He entered Owens College when he was 14 years old, where he became interested in experimental physics, though he had initially intended to pursue a career in engineering. Thomson’s father died only a few years into his college studies, making it financially difficult for Thomson to remain in school. However, through the efforts of his family and scholarships he continued at Owens College until 1876. He then transferred to Trinity College, Cambridge, on a mathematics scholarship. He remained associated with Cambridge University in varying capacities the rest of his life. In 1880, Thomson received a bachelor’s degree in mathematics and became second wrangler, a title bestowed on the second highest-scoring individual on the Cambridge mathematics exams.

Thomson atom model. On discharge of electricity through gases, it became clear that an atom consists of positive and negative charges. Thomson tried to explain the arrangement of positive charge and the electrons inside the atom. According to him, an atom is a sphere of positive charge having a radius of the order of 10-10 m. The Intel Atom processor and 4GB of RAM allow smooth multitasking, while the 4000 mAh lithium-ion battery offers up to seven hours of use. This Thomson Neo laptop has a 10.1-inch WSVGA display and Intel HD 400 integrated graphics for clear visuals, and the 64GB of eMMC storage provide fast startups. Thomson model of atom is the structure of an atom proposed by the scientist, J.J.Thomson, who was the first person to discover the electron. Soon after the discovery of the electron, the atomic model was proposed saying that the structure of an atom is like a “plum pudding”. Thomson model of atom is described base on three main facts.

Following graduation, Thomson became a Fellow at Trinity College and began work at the Cavendish Laboratory, part of the Cambridge Physics Department. In 1883, he became a lecturer at Cambridge and the following year was appointed Cavendish Professor of Experimental Physics, becoming the successor to Lord Rayleigh. Also in 1884, the Royal Society of London elected Thomson as a Fellow. The receipt of such considerable honors by so young a scientist was highly unusual, but was largely the result of Thomson’s significant early work expanding James Clerk Maxwell’s theories of electromagnetism. Coverage of these efforts, which continued over many years, appeared in Thomson’s 1892 treatise Notes on Recent Researches in Electricity and Magnetism.

In the early 1890s, much of Thomson’s research focused on electrical conduction in gases. During a visit to the United States in 1896, he gave a series of lectures discussing his findings. In 1897, the lectures were published as Discharge of Electricity through Gases. That same year, when Thomson returned to Cambridge, he made his most significant scientific discovery, that of the electron (which he initially referred to as the corpuscle). On April 30, 1897, Thomson made his discovery public while giving a lecture to the Royal Institution. The evidence he produced in support of his theoretical claims was culled from a series of innovative experiments with cathode ray tubes. In one experiment, Thomson attempted to use magnetism to see if negative charge could be segregated from cathode rays, in another he tried to deflect the rays with an electric field, and in a third he assessed the charge-to-mass ratio of the rays. These and additional studies carried out by Thomson and others quickly led to widespread acceptance of Thomson’s discovery.

Once the existence of the electron was accepted, the next step was to consider how the particles were incorporated into the atom. Thomson was initially a strong proponent of what is commonly called the plum-pudding atomic model or the Thomson atomic model, although many other representations of the atom were suggested by his contemporaries. According to Thomson’s view, each atom was a positively charged sphere with electrons scattered throughout (like bits of fruit in a plum pudding). He maintained this notion until experimental research and theoretical work indicated that the atomic model described in 1911 by Ernest Rutherford, a former student of Thomson, was much more likely. The Rutherford atomic model described the structure of the atom as a positively charged nucleus around which negatively charged electrons circulated. Research since that time has resulted in the abandonment of the Rutherford model in favor of other atomic models.

Throughout most of his life, Thomson was a leading scientific figure in Britain. He held a variety of administrative positions and received many prestigious awards in addition to the Nobel Prize. Thomson served as president of the Royal Society from 1915 to 1920, and was awarded several medals by the organization, including the Royal Medal (1894), the Hughes Medal (1902) and their highest honor, the Copley Medal (1914). In 1908, the royal family honored Thomson with knighthood, and the following year he was elected president of the British Association for the Advancement of Science. His contributions were further recognized with the Order of Merit (1912), election as a master of Trinity College (1918) and honorary degrees from universities around the globe.

Thomson married in 1890. His wife was Rose Elisabeth Paget, daughter of Sir George E. Paget, Regius Professor of Physic at Cambridge. The couple had two children. Their son, George Paget Thomson, followed in his father’s footsteps, winning the Nobel Prize in Physics for work involving the electron.

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:

... 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.

Gambar Atom Thomson

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.

Kelemahan Teori Atom Thomson

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]

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.

Joseph John Thomson Atom