Shortly after the discovery of the subatomic particles of an atom, scientists were eager to discover the distribution of these particles within the atom, various atomic models were proposed to explain the structure of the atom. Learn in this article about the Thomson Atomic Model.
Thomson Atomic Model
In 1898, Joseph John Thomson proposed the first of many atomic models to come, he stated that an atom is shaped like a sphere with a radius of about 10-10 m, where the positive charge is evenly distributed, the electrons are embedded in this sphere to give a more stable electrostatic arrangement.
An important aspect of this model is that it assumes that the mass of the atom is uniformly distributed over the atom, the Thomson's atomic theory was successful in explaining the general neutrality of the atom.
However, his proposals were not permanent with the effects of the experiments that were done later. In the year 1906, Thomson was awarded the Nobel Prize in Physics for his hypotheses and experiments on the conduction of electricity by gases.
Thomson thought that an electron is two thousand times lighter than a proton and believed that an atom is made up of thousands of electrons, in this model of atomic structure, he imagined that the atoms were surrounded by a cloud that has positive and negative charges.
The demonstration of the ionization of air by X-rays was also made by him, together with the Rutherford Atomic ModelThey were the first to show that Thomson's model of an atom is similar to a plum pudding.
Thomson argued that atoms are similar spheres of positively packed matter in which electrons are embedded, distinguished as the plum pudding model, had to be dropped for both theoretical and practical reasons in favor of Rutherford's atomic sample, in the that the electrons represent orbits about a small positive nucleus.
Features
Thomson arrived at his atomic model from several observations, the first being that Roentgen's newly discovered X-rays were capable of ionizing air molecules, until then the only way to ionize was by chemically separating ions in a solution.
But the English physicist successfully ionized even monatomic gases such as helium, through X-rays, this led him to profess that the charge inside the atom could be separated and therefore was not inseparable, he also paid attention that the cathode rays could be deflected by electric and magnetic fields.
So Thomson devised a model that correctly explained the fact that the atom is electrically neutral and that cathode rays are composed of negatively charged particles.
Using experimental reality, Thomson determined the atom as follows:
- The atom is an electrically neutral solid circle with a radius of approximately 10-10 m.
- The positive charge is more or less evenly distributed throughout the sphere.
- The atom has negatively saturated "corpuscles" that assert its neutrality.
- These corpuscles are the same for all matter.
- When the atom is in equilibrium, there is n corpuscles normally arranged in rings within the circle of positive charge.
- The mass of the atom is spread out evenly.
Limitations
Thomson had several limitations when applying his theory:
- He was unable to explain the permanence of an atom because his model was unable to reveal how a positive charge immobilizes the negatively charged electrons in an atom, thus this theory never succeeded in explaining the focus of the nucleus in an atom.
- Thomson's model could not reveal the scattering of alpha particles by thin metal plates.
- There is no experimental evidence in its support.
Although the Thomson's model it was not a precise model to explain the atomic structure, it proved to be the basis for the development of other atomic models, the study of the atom and its structure has paved the way for numerous inventions that have played an important role in the development of humanity.
Who was Joseph John Thomson?
"Joseph John Thomson was born on 18 December 1856 at Cheetham, near Manchester, of Scottish parents, after studying engineering at Owens College, he attended Trinity College, Cambridge, before becoming, in 1884, Cavendish Professor at Cambridge University for the chair of physics.
In 1890 he married Rose Paget, who would give him two children; in 1894, however, he became director of the Cavendish Laboratory in Cambridge, a post he held until 1919.
Author of numerous works related to Maxwell's electromagnetism, Thomson devoted himself to the study of the origin of cathode rays, at the center of scientific debate at the time.
In 1897, two years after Perrin's discovery (which had shown that cathode rays have negative charges), he succeeded in deflecting cathode rays into an electric field, hence the belief that the composition of cathode rays are negative electric charges, electrons.
The academic determines the most important characteristics of these particles, subjecting the cathode rays to the simultaneous action of two fields: one magnetic and the other electric, in this way he manages to measure the speed and the relationship between charge and mass.
Taking into account the migration of the fog droplets in the electric field, moreover, he arrives at a first evaluation related to the mass of the electron.
In the same year, Thomson demonstrates the emission of electrons in the thermoelectronic effect and in the photoelectric effect and therefore, with the collaboration of Ernest Rutherford, performs a method to measure the nature of the radiation produced by radioactive substances, based on ionization acting on a gas.
The discovery of electrons is used to study the phenomenon of gases traversed by the passage of electricity, the explanation found by the physicist consists of the ionization theory, which won the Nobel Prize in 1906, however, the discovery of the electron brings up again the question of the Levels of Organization of Matter.
In 1904 Thomson proposed a model of the atom composed of continuously distributed positive electricity, in which a number of electrons move in concentric circular paths that allow the positive charge to be compensated.
Although outclassed by Rutherford's atomic model, Thomson's hypothesis proves to be decidedly important as it focuses on the problem of radioactive instabilities that characterizes any atomic model including electrons based on classical physics.
Impact of the Thomson Model
El Thomson's model was accepted as the best available atomic theory, what distinguishes Thomson's theory is its assignment of a specific internal distribution to the atom, as well as a set of dynamical assumptions.
In 1899, in a paper addressed to the British Association for the Advancement of Science, Thomson presented the essential ingredients of his model without any mathematical formula:
"I consider that the atom contains a large number of smaller bodies that I will call corpuscles, in the normal atom, this set of corpuscles forms a system that is electrically neutral."
Although the individual corpuscles behave like negative ions when assembled into a neutral atom, the negative effect is balanced by something that makes the space through which the corpuscles extend, causing it to act as if it had an equal positive electrical charge. in quantity to the sum of the negative charges in the corpuscles.
Thomson built his atomic theory to lead to mathematical analysis where stability, as the title indicates, plays a critical role, the atom in equilibrium has n corpuscles and are arranged at equal angular intervals in rings within a positively electrified sphere, each corpuscle carrying a charge of negative electricity.
In 1907 Thomson published a book: The Corpuscular Theory of Matter, based on a course of lectures he had given at the Royal Institution in the spring of 1906, in these lectures Thomson discussed the theory of the constitution of matter which, to Thomson, supposes that the various properties of matter can be considered to be derived from electrical effects.
