What model of the structure of the atom did Rutherford propose. Some historical and modern models of the atom

Historical models1 of the atom reflect the levels of knowledge corresponding to a certain period in the development of science.

The first stage in the development of atomic models was characterized by the absence of experimental data on its structure.

Explaining the phenomena of the microcosm, scientists looked for analogies in the macrocosm, relying on the laws of classical mechanics.

J. Dalton, the creator of chemical atomism (1803), assumed that atoms of the same chemical element are the same spherical smallest, and therefore, indivisible particles.

The French physicist Jean Baptiste Perrin (1901) proposed a model that actually anticipated the "planetary" model. According to this model, a positively charged nucleus is located in the center of the atom, around which negatively charged electrons move in certain orbits, like planets around the Sun. The Perrin model did not attract the attention of scientists, since it gave only a qualitative, but not a quantitative, characteristic of the atom (in Fig. 7 this is shown by the discrepancy between the charge of the atomic nucleus and the number of electrons).

In 1902, the English physicist William Thomson (Kelvin) developed the idea of ​​an atom as a positively charged spherical particle, inside which negatively charged electrons oscillate (radiate and absorb energy). Kelvin drew attention to the fact that the number of electrons is equal to the positive charge of the sphere, therefore, as a whole, the atom has no electric charge (Fig. 7).

A year later, the German physicist Philipp Lenard proposed a model according to which the atom is a hollow sphere, inside which there are electric dipoles (dynamides). The volume occupied by these dipoles is much less than the volume of the sphere, and the main part of the atom is empty.

According to the ideas of the Japanese physicist Gontaro (Hantaro) Nagaoka (1904), a positively charged nucleus is located in the center of the atom, and electrons move in space around the nucleus in flat rings resembling the rings of the planet Saturn (this model was called the "Saturnian" atom). Most scientists have not paid attention to the ideas of Nagaoka, although they to some extent have something in common with the modern idea of ​​​​the atomic orbital.

None of the considered models (Fig. 7) explained how the properties of chemical elements are related to the structure of their atoms.

Rice. 7. Some historical models of the atom

In 1907, J. J. Thomson proposed a static model of the structure of the atom, representing the atom as a spherical particle charged with positive electricity, in which negatively charged electrons are uniformly distributed ( model"pudding", Fig. 7).

Mathematical calculations have shown that the electrons in an atom must be located on concentrically arranged rings. Thomson did very important conclusion: the reason for the periodic change in the properties of chemical elements is associated with the features electronic structure their atoms. Thanks to this, Thomson's model of the atom was highly appreciated by his contemporaries. However, it did not explain certain phenomena, for example, the scattering of α-particles during their passage through metal plate.

Based on his ideas about the atom, Thomson derived a formula for calculating the average deviation of α-particles, and this calculation showed that the probability of scattering of such particles at large angles is close to zero. However, it has been experimentally proved that approximately one in eight thousand alpha particles falling on gold foil is deflected through an angle greater than 90°. This contradicted Thomson's model, which assumed deviations only through small angles.

Ernest Rutherford, summarizing experimental data, in 1911 proposed a "planetary" (sometimes called "nuclear") model of the structure of the atom, according to which 99.9% of the atom's mass and its positive charge are concentrated in a very small nucleus, and negatively charged electrons, the number which is equal to the charge of the nucleus, revolve around it, like the planets of the solar system1 (Fig. 7).

Rutherford, together with his students, set up experiments that made it possible to investigate the structure of the atom (Fig. 8). A stream of positively charged particles (α-particles) was directed to the surface of a thin metal (gold) foil 2 from a source of radioactive radiation 1. On their way, a fluorescent screen 3 was installed, which made it possible to observe the direction of the further movement of α-particles.

Rice. 8. Rutherford's experience

It was found that most of the α-particles passed through the foil, practically without changing their direction. Only individual particles (an average of one in ten thousand) were deflected and flew almost in the opposite direction. It was concluded that most of the atom's mass is concentrated in the positively charged nucleus, which is why the α-particles are so strongly deflected (Fig. 9).

Rice. 9. Scattering of α-particles by an atomic nucleus

Electrons moving in an atom, in accordance with the laws of electromagnetism, must radiate energy and, losing it, be attracted to the oppositely charged nucleus and, therefore, "fall" on it. This should lead to the disappearance of the atom, but since this did not happen, it was concluded that this model was inadequate.

At the beginning of the 20th century, the German physicist Max Planck and theoretical physicist Albert Einstein created the quantum theory of light. According to this theory, radiant energy, such as light, is emitted and absorbed not continuously, but in separate portions (quanta). Moreover, the value of the energy quantum is not the same for different radiations and is proportional to the frequency of oscillations of the electromagnetic wave: E = hν, where h – Planck's constant equal to 6.6266 10 -34 J s, ν is the radiation frequency. This energy is carried by particles of light - photons.

In an attempt to artificially combine the laws of classical mechanics and quantum theory, the Danish physicist Niels Bohr in 1913 supplemented Rutherford's model of the atom with two postulates about a stepwise (discrete) change in the energy of electrons in an atom. Bohr believed that an electron in a hydrogen atom can only be located on well-defined stationary orbits, whose radii are related to each other as squares natural numbers (1 2: 2 2: 3 2: ... :p 2). Electrons move around atomic nucleus in stationary orbits. The atom is in a stable state, without absorbing or emitting energy - this is Bohr's first postulate. According to the second postulate, energy emission occurs only when an electron moves to an orbit closer to the atomic nucleus. When an electron moves to a more distant orbit, energy is absorbed by the atom. This model was improved in 1916 by the German theoretical physicist Arnold Sommerfeld, who pointed out the motion of electrons along elliptical orbits.

planetary model, due to its visibility and Bohr's postulates, long time used to explain atomic and molecular phenomena. However, it turned out that the motion of an electron in an atom, the stability and properties of an atom, in contrast to the motion of the planets and the stability of the solar system, cannot be described by the laws of classical mechanics. This mechanics is based on Newton's laws, and the subject of its study is the movement of macroscopic bodies, performed at speeds that are small compared to the speed of light. To describe the structure of the atom, it is necessary to apply the concepts of quantum (wave) mechanics about the dual corpuscular-wave nature of microparticles, which were formulated in the 1920s by theoretical physicists: the Frenchman Louis de Broglie, the Germans Werner Heisenberg and Erwin Schrödinger, the Englishman Paul Dirac and others.

In 1924, Louis de Broglie put forward the hypothesis that the electron has wave properties (the first principle of quantum mechanics) and proposed a formula for calculating its wavelength. The stability of an atom is explained by the fact that the electrons in it do not move in orbits, but in certain regions of space around the nucleus, called atomic orbitals. The electron occupies almost the entire volume of the atom and cannot "fall on the nucleus" located in its center.

In 1926, Schrödinger, continuing the development of L. de Broglie's ideas about the wave properties of an electron, empirically selected a mathematical equation similar to the string vibration equation, which can be used to calculate the binding energies of an electron in an atom at different energy levels. This equation has become the basic equation of quantum mechanics.

The discovery of the wave properties of the electron showed that the dissemination of knowledge about the macrocosm to the objects of the microcosm is unlawful. In 1927, Heisenberg established that it is impossible to determine the exact position in space of an electron with a certain speed, therefore, ideas about the motion of an electron in an atom are of a probabilistic nature (the second principle of quantum mechanics).

The Quantum Mechanical Model of the Atom (1926) describes the state of the atom in terms of mathematical functions and has no geometric expression (Fig. 10). Such a model does not consider the dynamic nature of the structure of the atom and the question of the size of an electron as a particle. It is believed that electrons occupy certain energy levels and emit or absorb energy during transitions to other levels. On fig. 10 energy levels are shown schematically as concentric rings located at different distances from the atomic nucleus. The arrows show the transitions of electrons between energy levels and emission of photons accompanying these transitions. The scheme is shown qualitatively and does not reflect the real distances between energy levels, which can differ from each other by dozens of times.

In 1931, the American scientist Gilbert White first proposed a graphical representation of atomic orbitals and an "orbital" model of the atom (Fig. 10). Models of atomic orbitals are used to reflect the concept of "electron density" and to demonstrate the distribution of negative charge around a nucleus in an atom or a system of atomic nuclei in a molecule.

Rice. 10. Historical and modern models atom

In 1963, the American artist, sculptor and engineer Kenneth Snelson proposed a "ring-faced model" of the electron shells of an atom (Fig. 10), which explains the quantitative distribution of electrons in an atom over stable electron shells. Each electron is modeled by a ring magnet (or a closed circuit with an electric current having a magnetic moment). Ring magnets are attracted to each other and form symmetrical shapes from rings - ringhedra. The presence of two poles in magnets imposes a limitation on possible options assemblies of rings. Models of stable electron shells are the most symmetrical figures of the rings, composed taking into account the presence of their magnetic properties.

The presence of a spin in an electron (see Section 5) is one of the main reasons for the formation of stable electron shells in an atom. Electrons form pairs with opposite spins. The ring-faced model of an electron pair, or a filled atomic orbital, is two rings located in parallel planes on opposite sides of the atomic nucleus. When more than one pair of electrons is located near the nucleus of an atom, the rings-electrons are forced to mutually orient themselves, forming an electron shell. In this case, closely spaced rings have different directions of magnetic lines of force, which is denoted different color rings representing electrons.

Model experiment shows that the most stable of all possible ring-faced models is the model of 8 rings. Geometrically, the model is formed in such a way as if an atom in the form of a sphere was divided into 8 parts (divided three times in half) and one ring-electron was placed in each part. In ring-faced models, rings of two colors are used: red and blue, which reflect positive and negative meaning spin of an electron.

The "wave-faced model" (Fig. 10) is similar to the "ring-faced" one, with the difference that each electron of an atom is represented by a "wave" ring, which contains an integer number of waves (as proposed by L. de Broglie).

The interaction of the electrons of the electron shell on this model of the atom is shown by the coincidence of the points of contact of the blue and red "wave" rings with the nodes of the standing waves.

Models of the atom have the right to exist and the limits of application. Any model of an atom is an approximation that reflects in a simplified form a certain part of the knowledge about the atom. But none of the models fully reflects the properties of the atom or its constituent particles.

Many models today are only of historical interest. When building models of microworld objects, scientists relied on what can be directly observed. This is how the models of Perrin and Rutherford (an analogy with the structure of the solar system), Nagaoka (a kind of planet Saturn), Thomson ("raisin pudding") appeared. Some ideas were discarded (Lenard's dynamic model), others were revisited after a while, but at a new, higher level. theoretical level: the models of Perrin and Kelvin were developed in the models of Rutherford and Thomson. Ideas about the structure of the atom are constantly being improved. How accurate is the modern - "quantum-mechanical" model - time will tell. That is why a question mark is drawn at the top of the spiral, symbolizing the path of cognition (Fig. 7).

They became an important step in the development of physics. Rutherford's model was of great importance. The atom as a system and the particles that make it up has been studied more accurately and in detail. This led to the successful development of such a science as nuclear physics.

Ancient ideas about the structure of matter

The assumption that the surrounding bodies are composed of the smallest particles was made in ancient times. The thinkers of that time represented the atom as the smallest and indivisible particle of any substance. They argued that there is nothing in the universe smaller than an atom. Such views were held by the great ancient Greek scientists and philosophers - Democritus, Lucretius, Epicurus. The hypotheses of these thinkers today are united under the name "ancient atomism".

Medieval performances

The times of antiquity have passed, and in the Middle Ages there were also scientists who made various assumptions about the structure of substances. However, the predominance of religious philosophical views and the power of the church at that period of history nipped in the bud any attempts and aspirations of the human mind to materialistic scientific conclusions and discoveries. As you know, the medieval Inquisition behaved very unfriendly with representatives of the scientific world of that time. It remains to be said that the then bright minds had an idea that came from antiquity about the indivisibility of the atom.

Research in the 18th and 19th centuries

The 18th century was marked by serious discoveries in the field of the elementary structure of matter. Largely thanks to the efforts of scientists such as Antoine Lavoisier, Mikhail Lomonosov and Independently of each other, they were able to prove that atoms really exist. But the question about them internal structure remained open. The end of the 18th century was marked by such significant event in scientific world, as the discovery by D. I. Mendeleev of the periodic system of chemical elements. This was a truly powerful breakthrough of that time and lifted the veil over the understanding that all atoms have a single nature, that they are related to each other. Later, in the 19th century, another important step towards unraveling the structure of the atom was the proof that any of them contains an electron. The work of the scientists of this period prepared fertile ground for the discoveries of the 20th century.

Thomson experiments

The English physicist John Thomson proved in 1897 that the composition of atoms includes electrons with a negative charge. At this stage, the false ideas that the atom is the limit of the divisibility of any substance were finally destroyed. How did Thomson manage to prove the existence of electrons? The scientist in his experiments placed electrodes in highly rarefied gases and passed electricity. The result was cathode rays. Thomson carefully studied their features and found that they are a stream of charged particles that move at great speed. The scientist was able to calculate the mass of these particles and their charge. He also found out that they could not be converted into neutral particles because electric charge is the basis of their nature. So were Thomson and the creator of the world's first model of the structure of the atom. According to her, an atom is a bunch of positively charged matter, in which negatively charged electrons are evenly distributed. This structure explains the general neutrality of atoms, since opposite charges balance each other. The experiments of John Thomson became invaluable for the further study of the structure of the atom. However, many questions remained unanswered.

Rutherford's research

Thomson discovered the existence of electrons, but he failed to find positively charged particles in the atom. corrected this misunderstanding in 1911. During experiments, studying the activity of alpha particles in gases, he discovered that there are positively charged particles in the atom. Rutherford saw that when rays pass through a gas or through a thin metal plate, a small number of particles sharply deviate from the trajectory of motion. They were literally thrown back. The scientist guessed that this behavior is due to a collision with positively charged particles. Such experiments allowed the physicist to create Rutherford's model of the structure of the atom.

planetary model

Now the scientist's ideas were somewhat different from the assumptions made by John Thomson. Their models of atoms also became different. allowed him to create a completely new theory in this area. The discoveries of the scientist were decisive for further development physics. Rutherford's model describes an atom as a nucleus located in the center, and electrons moving around it. The nucleus has a positive charge, and the electrons have a negative charge. Rutherford's model of the atom assumed the rotation of electrons around the nucleus along certain trajectories - orbits. The discovery of the scientist helped explain the reason for the deviation of alpha particles and became the impetus for the development of the nuclear theory of the atom. In Rutherford's model of the atom, there is an analogy with the movement of the planets of the solar system around the sun. This is a very accurate and vivid comparison. Therefore, the Rutherford model, in which the atom moves around the nucleus in an orbit, was called planetary.

Works by Niels Bohr

Two years later, the Danish physicist Niels Bohr tried to combine ideas about the structure of the atom with quantum properties. luminous flux. nuclear model Rutherford's atom was put by scientists as the basis of his new theory. According to Bohr, atoms revolve around the nucleus in circular orbits. Such a trajectory of motion leads to the acceleration of electrons. In addition, the Coulomb interaction of these particles with the center of the atom is accompanied by the creation and consumption of energy to maintain the spatial electromagnetic field due to the movement of electrons. Under such conditions, negatively charged particles must someday fall onto the nucleus. But this does not happen, which indicates the greater stability of atoms as systems. Niels Bohr realized that the laws of classical thermodynamics described by Maxwell's equations do not work in intraatomic conditions. Therefore, the scientist set himself the task of deriving new patterns that would be valid in the world elementary particles.

Bohr's postulates

Largely due to the fact that Rutherford's model existed, the atom and its components were well studied, Niels Bohr was able to approach the creation of his postulates. The first of them says that an atom has at which it does not change its energy, while electrons move in orbits without changing their trajectory. According to the second postulate, when an electron moves from one orbit to another, energy is released or absorbed. It is equal to the difference between the energies of the previous and subsequent states of the atom. In this case, if the electron jumps to an orbit closer to the nucleus, then radiation occurs and vice versa. Despite the fact that the movement of electrons bears little resemblance to an orbital trajectory located strictly in a circle, Bohr's discovery provided an excellent explanation for the existence of a line spectrum. At about the same time, physicists Hertz and Frank, who lived in Germany, confirmed Niels Bohr's theory of the existence of stationary, stable states of the atom and the possibility of changing the values ​​of atomic energy.

Collaboration of two scientists

By the way, Rutherford long time could not determine Scientists Marsden and Geiger tried to re-check the statements of Ernest Rutherford and, as a result of detailed and careful experiments and calculations, came to the conclusion that it is the nucleus that is the most important characteristic of the atom, and all its charge is concentrated in it. Later it was proved that the value of the charge of the nucleus is numerically equal to the ordinal number of the element in periodic system elements of D. I. Mendeleev. Interestingly, Niels Bohr soon met Rutherford and fully agreed with his views. Subsequently, scientists worked together for a long time in the same laboratory. Rutherford's model, the atom as a system consisting of elementary charged particles - all this Niels Bohr considered fair and forever put aside his electronic model. Joint scientific activity scientists was very successful and has borne fruit. Each of them delved into the study of the properties of elementary particles and made significant discoveries for science. Later, Rutherford discovered and proved the possibility of nuclear decomposition, but this is a topic for another article.

Details Category: Physics of the atom and atomic nucleus Posted on 03/10/2016 18:27 Views: 4106

Ancient Greek and ancient Indian scientists and philosophers believed that all the substances around us consist of tiny particles that do not divide.

They were sure that there was nothing in the world that would be smaller than these particles, which they called atoms . And, indeed, later the existence of atoms was proved by such famous scientists as Antoine Lavoisier, Mikhail Lomonosov, John Dalton. The atom was considered indivisible until the end of the 19th - beginning of the 20th century, when it turned out that this was not so.

The discovery of the electron. Thomson model of the atom

Joseph John Thomson

In 1897, the English physicist Joseph John Thomson, studying experimentally the behavior of cathode rays in magnetic and electric fields, found out that these rays are a stream of negatively charged particles. The speed of movement of these particles was below the speed of light. Therefore, they had mass. Where did they come from? The scientist suggested that these particles are part of the atom. He called them corpuscles . Later they were called electrons . Thus the discovery of the electron put an end to the theory of the indivisibility of the atom.

Thomson model of the atom

Thomson proposed the first electronic model of the atom. According to it, an atom is a sphere, inside of which there is a charged substance, the positive charge of which is evenly distributed throughout the volume. And in this substance, like raisins in a bun, electrons are interspersed. In general, the atom is electrically neutral. This model was called the "plum pudding model".

But Thomson's model turned out to be wrong, which was proven British physicist Sir Ernest Rutherford.

Rutherford's experience

Ernest Rutherford

How is an atom actually arranged? Rutherford gave an answer to this question after his experiment, carried out in 1909 together with the German physicist Hans Geiger and the New Zealand physicist Ernst Marsden.

Rutherford's experience

The purpose of the experiment was to study the atom with the help of alpha particles, a focused beam of which, flying at great speed, was directed to the thinnest gold foil. Behind the foil was a luminescent screen. When particles collided with it, flashes appeared that could be observed under a microscope.

If Thomson is right, and the atom is made up of a cloud of electrons, then the particles should easily fly through the foil without being deflected. Since the mass of the alpha particle exceeded the mass of the electron by about 8000 times, the electron could not act on it and deviate its trajectory at a large angle, just as a 10 g pebble could not change the trajectory of a moving car.

But in practice, everything turned out differently. Most of the particles actually flew through the foil, practically not deviating or deviating by a small angle. But some of the particles deviated quite significantly or even bounced back, as if there was some kind of obstacle in their path. As Rutherford himself said, it was as incredible as if a 15-inch projectile bounced off a piece of tissue paper.

What caused some alpha particles to change direction so much? The scientist suggested that the reason for this was a part of the atom, concentrated in a very small volume and having a positive charge. He called her the nucleus of an atom.

Rutherford's planetary model of the atom

Rutherford model of the atom

Rutherford came to the conclusion that the atom consists of a dense positively charged nucleus located in the center of the atom and electrons that have a negative charge. Almost all the mass of an atom is concentrated in the nucleus. In general, the atom is neutral. The positive charge of the nucleus is equal to the sum of the negative charges of all the electrons in the atom. But the electrons are not embedded in the nucleus, as in Thomson's model, but revolve around it like the planets revolve around the sun. The rotation of electrons occurs under the action of the Coulomb force acting on them from the nucleus. The speed of rotation of electrons is huge. Above the surface of the core, they form a kind of cloud. Each atom has its own electron cloud, negatively charged. For this reason, they do not "stick together", but repel each other.

Due to its similarity with the solar system, Rutherford's model was called planetary.

Why does the atom exist

However, Rutherford's model of the atom failed to explain why the atom is so stable. After all, according to the laws of classical physics, an electron, rotating in orbit, moves with acceleration, therefore, it radiates electromagnetic waves and loses energy. In the end, this energy must run out, and the electron must fall into the nucleus. If this were the case, the atom could only exist for 10 -8 s. But why isn't this happening?

The reason for this phenomenon was later explained by the Danish physicist Niels Bohr. He suggested that the electrons in an atom move only in fixed orbits, which are called "allowed orbits". Being on them, they do not radiate energy. And the emission or absorption of energy occurs only when an electron moves from one allowed orbit to another. If this is a transition from a distant orbit to one closer to the nucleus, then energy is radiated, and vice versa. The radiation occurs in portions, which are called quanta.

Although the model described by Rutherford could not explain the stability of the atom, it allowed significant progress in the study of its structure.

Planetary model of the atom

Planetary model of an atom: nucleus (red) and electrons (green)

Planetary model of the atom, or Rutherford model, - historical model of the structure of the atom, which was proposed by Ernest Rutherford as a result of an experiment with alpha particle scattering. According to this model, the atom consists of a small positively charged nucleus, in which almost the entire mass of the atom is concentrated, around which electrons move, just as the planets move around the sun. The planetary model of the atom corresponds to modern ideas about the structure of the atom, taking into account the fact that the movement of electrons is of a quantum nature and is not described by the laws of classical mechanics. Historically, Rutherford's planetary model succeeded Joseph John Thomson's "plum pudding model", which postulates that negatively charged electrons are placed inside a positively charged atom.

Rutherford proposed a new model for the structure of the atom in 1911 as a conclusion from an experiment on the scattering of alpha particles on gold foil, carried out under his leadership. With this scattering, unexpectedly a large number of alpha particles were scattered at large angles, which indicated that the scattering center has small size and it contains a significant electric charge. Rutherford's calculations showed that a scattering center, positively or negatively charged, must be at least 3000 times smaller size an atom, which at that time was already known and estimated to be about 10 -10 m. Since at that time the electrons were already known, and their mass and charge were determined, the scattering center, which was later called the nucleus, must have had an opposite charge to the electrons. Rutherford did not link the amount of charge to atomic number. This conclusion was made later. And Rutherford himself suggested that the charge is proportional to the atomic mass.

The disadvantage of the planetary model was its incompatibility with the laws of classical physics. If electrons move around the nucleus like a planet around the Sun, then their movement is accelerated, and, therefore, according to the laws of classical electrodynamics, they should radiate electromagnetic waves, lose energy and fall on the nucleus. The next step in the development of the planetary model was the Bohr model, postulating other, different from the classical, laws of electron motion. Completely the contradictions of electrodynamics were able to solve quantum mechanics.

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planetary model of the atom- planetinis atomo modelis statusas T sritis fizika atitikmenys: angl. planetary atom model vok. Planetenmodell des Atoms, n rus. planetary model of the atom, f pranc. modele planétaire de l'atome, m … Fizikos terminų žodynas

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STRUCTURE OF THE ATOM- (see) is built from elementary particles of three types (see), (see) and (see), forming a stable system. The proton and neutron are a part of atomic (see), electrons form an electron shell. Forces act in the nucleus (see), thanks to which ... ... Great Polytechnic Encyclopedia

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Άτομο

corpuscle- Helium atom Atom (another Greek ἄτομος indivisible) is the smallest part of a chemical element, which is the carrier of its properties. An atom consists of an atomic nucleus and an electron cloud surrounding it. The nucleus of an atom consists of positively charged protons and ... ... Wikipedia

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Lecture: Planetary model of the atom

The structure of the atom

The most accurate way to determine the structure of any substance is spectral analysis. The radiation of each atom of an element is exclusively individual. However, before understanding how spectral analysis occurs, let's figure out what structure an atom of any element has.

The first assumption about the structure of the atom was presented by J. Thomson. This scientist has been studying atoms for a long time. Moreover, it is he who owns the discovery of the electron - for which he received Nobel Prize. The model that Thomson proposed had nothing to do with reality, but served as a strong enough incentive for Rutherford to study the structure of the atom. The model proposed by Thomson was called "raisin pudding".

Thomson believed that the atom is a solid ball with a negative electrical charge. To compensate for it, electrons are interspersed in the ball, like raisins. In sum, the charge of the electrons coincides with the charge of the entire nucleus, which makes the atom neutral.

During the study of the structure of the atom, it was found that all atoms in solids commit oscillatory movements. And, as you know, any moving particle radiates waves. That is why each atom has its own spectrum. However, these statements did not fit into the Thomson model in any way.

Rutherford's experience

To confirm or disprove Thomson's model, Rutherford proposed an experiment that resulted in the bombardment of an atom of some element by alpha particles. As a result of this experiment, it was important to see how the particle would behave.

Alpha particles were discovered as a result of the radioactive decay of radium. Their streams were alpha rays, each particle of which had a positive charge. As a result of numerous studies, it was determined that the alpha particle is like a helium atom, in which there are no electrons. Using current knowledge, we know that the alpha particle is the nucleus of helium, while Rutherford believed that these were helium ions.

Each alpha particle had tremendous energy, as a result of which it could fly at the atoms in question with high speed. Therefore, the main result of the experiment was to determine the particle deflection angle.

For the experiment, Rutherford used thin gold foil. He directed high-speed alpha particles at it. He assumed that as a result of this experiment, all particles would fly through the foil, and with small deviations. However, in order to find out for sure, he instructed his students to check if there were any large deviations in these particles.

The result of the experiment surprised absolutely everyone, because many particles not only deviated by a sufficiently large angle - some deflection angles reached more than 90 degrees.

These results surprised absolutely everyone, Rutherford said that it felt like a piece of paper was placed in the path of the projectiles, which did not allow the alpha particle to penetrate inside, as a result of which it turned back.

If the atom were really solid, then it would have to have some electric field, which slowed down the particle. However, the strength of the field was not enough to stop her completely, let alone push her back. This means that Thomson's model was refuted. So Rutherford started working on a new model.

Rutherford model

To get this result of the experiment, it is necessary to concentrate the positive charge in a smaller amount, resulting in a larger electric field. According to the field potential formula, one can determine required size a positive particle that could repel an alpha particle in the opposite direction. Its radius should be of the order of maximum 10 -15 m. That is why Rutherford proposed the planetary model of the atom.

This model is named so for a reason. The fact is that inside the atom there is a positively charged nucleus, similar to the Sun in the solar system. Electrons revolve around the nucleus like planets. solar system is designed in such a way that the planets are attracted to the Sun with the help of gravitational forces, however, they do not fall to the surface of the Sun as a result of the available velocity that keeps them in their orbit. The same thing happens with electrons - Coulomb forces attract electrons to the nucleus, but due to rotation, they do not fall on the surface of the nucleus.

One assumption of Thomson turned out to be absolutely correct - the total charge of electrons corresponds to the charge of the nucleus. However, as a result of a strong interaction, electrons can be knocked out of their orbit, as a result of which the charge is not compensated and the atom turns into a positively charged ion.

Very important information regarding the structure of the atom is that almost all the mass of the atom is concentrated in the nucleus. For example, a hydrogen atom has only one electron, whose mass is more than one and a half thousand times less than the mass of the nucleus.