Creation of a planetary model of the atom. School Encyclopedia

The idea that atoms are the smallest particles of matter first arose during the Ancient Greece. However, only at the end of the 18th century, thanks to the work of such scientists as A. Lavoisier, M. V. Lomonosov and some others, it was proved that atoms really exist. However, in those days, no one wondered what their internal structure was. Scientists still regarded atoms as the indivisible "bricks" that make up all matter.

Attempts to explain the structure of the atom

Who proposed the nuclear model first of all scientists? The first attempt to create a model of these particles belonged to J. Thomson. However, it cannot be called successful in the full sense of the word. After all, Thomson believed that the atom is a spherical and electrically neutral system. At the same time, the scientist assumed that the positive charge is distributed evenly over the volume of this ball, and inside it there is a negatively charged nucleus. All attempts by the scientist to explain the internal structure of the atom were unsuccessful. Ernest Rutherford is the one who proposed the nuclear model of the structure of the atom a few years after Thomson put forward his theory.

Research History

With the help of the study of electrolysis in 1833, Faraday was able to establish that the current in the electrolyte solution is a stream of charged particles, or ions. Based on these studies, he was able to determine the minimum charge of an ion. Also an important role in the development of this direction in physics was played by the domestic chemist D. I. Mendeleev. It was he who first raised in scientific circles the question that all atoms can have the same nature. We see that before Rutherford's nuclear model of the structure of the atom was first proposed, a variety of scientists carried out a large number of no less important experiments. They advanced the atomistic theory of the structure of matter forward.

First experiences

Rutherford is a truly brilliant scientist, because his discoveries turned the idea of ​​\u200b\u200bthe structure of matter upside down. In 1911, he was able to set up an experiment with which researchers were able to look into the mysterious depths of the atom, to get an idea of ​​​​what its internal structure is. The first experiments were carried out by the scientist with the support of other researchers, but the main role in the discovery still belonged to Rutherford.

Experiment

Using natural sources of radioactive radiation, Rutherford was able to build a cannon that emitted a stream of alpha particles. It was a box made of lead, inside of which was a radioactive substance. The cannon had a slit through which all the alpha particles hit the lead screen. They could fly out only through the slot. Several more screens stood in the way of this beam of radioactive particles.

They separated particles that deviated from the previously set direction. A strictly focused hit hit the target. As a target, Rutherford used thin sheet from gold foil. After the particles hit this sheet, they continued their movement and eventually hit the fluorescent screen, which was installed behind this target. When alpha particles hit this screen, flashes were recorded, by which the scientist could judge how many particles deviate from the original direction when colliding with the foil and what is the magnitude of this deviation.

Differences from previous experiences

Schoolchildren and students who are interested in those who proposed the nuclear model of the structure of the atom should know that similar experiments were carried out in physics before Rutherford. Them main idea was to collect as much information as possible about the structure of the atom from the deviations of particles from the original trajectory. All these studies led to the accumulation of a certain amount of information in science, provoked thinking about internal structure the smallest particles.

Already at the beginning of the 20th century, scientists knew that the atom contains electrons that have a negative charge. But among the majority of researchers, the prevailing opinion was that the atom from the inside is more like a grid filled with negatively charged particles. Such experiments made it possible to obtain a lot of information - for example, to determine the geometric dimensions of atoms.

genius guess

Rutherford noticed that none of his predecessors had ever tried to determine whether alpha particles could deviate at very large angles from their trajectory. The old model, sometimes called "raisin pudding" among scientists (because according to this model, the electrons in the atom are distributed like raisins in the pudding), simply did not allow the existence of dense structural components inside the atom. None of the scientists even bothered to consider this option. The researcher asked his student to re-equip the installation in such a way that large deviations of particles from the trajectory were also recorded - only in order to exclude such a possibility. Imagine the surprise of both the scientist and his student when it turned out that some particles fly apart at an angle of 180 o.

What's inside an atom?

We learned who proposed the nuclear model of the structure of the atom and what was the experience of this scientist. At that time, Rutherford's experiment was a real breakthrough. He was forced to conclude that inside the atom, most of the mass is enclosed in a very dense substance. Scheme nuclear model The structure of the atom is extremely simple: inside is a positively charged nucleus.

Other particles, called electrons, revolve around this nucleus. The rest is several orders of magnitude less dense. The arrangement of electrons inside an atom is not chaotic - the particles are arranged in order of increasing energy. The researcher called the internal parts of atoms nuclei. The names that the scientist introduced are still used in science.

How to prepare for the lesson?

Those schoolchildren who are interested in those who suggested the nuclear model of the structure of the atom can show off additional knowledge in the lesson. For example, you can tell how Rutherford, long after his experiments, liked to give an analogy for his discovery. The South African country is smuggled with weapons for the rebels, which are enclosed in bales of cotton. How can customs officers determine exactly where dangerous supplies are if the entire train is full of these bales? The customs officer can start shooting at the bales, and where the bullets will ricochet, and there is a weapon. Rutherford stressed that this is how his discovery was made.

Students who are preparing to answer on this topic in the lesson, it is advisable to prepare answers to the following questions:

1. Who proposed the nuclear model of the structure of the atom?

2. What was the meaning of the experiment?

3. Difference of the nuclear model from other models.

Significance of Rutherford's theory

The radical conclusions that Rutherford drew from his experiments made many of his contemporaries doubt the validity of this model. Even Rutherford himself was no exception - he published the results of his research only two years after the discovery. Taking as a basis the classical ideas about how microparticles move, he proposed a nuclear planetary model of the structure of the atom. In general, the atom has a neutral charge. Electrons move around the nucleus, just like the planets revolve around the sun. This movement occurs due to the Coulomb forces. At the moment, Rutherford's model has undergone significant refinement, but the discovery of the scientist does not lose its relevance today.

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 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. During this scattering, an unexpectedly 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.

disadvantage planetary model was its incompatibility with the laws of classical physics. If electrons move around the nucleus like planets around the Sun, then their movement is accelerated, and, therefore, according to the laws of classical electrodynamics, they should have radiated electromagnetic waves, lose energy and fall on the core. 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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See what the "Planetary Model of the Atom" is in other dictionaries:

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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The first information about the complex the structure of the atom were obtained in the study of the processes of passage electric current through liquids. In the thirties of the XIX century. experiments outstanding physicist M. Faraday was led to the idea that electricity exists in the form of separate unit charges.

The discovery of the spontaneous decay of atoms of some elements, called radioactivity, was direct evidence of the complexity of the structure of the atom. In 1902, English scientists Ernest Rutherford and Frederick Soddy proved that during radioactive decay, a uranium atom turns into two atoms - a thorium atom and a helium atom. This meant that atoms are not immutable, indestructible particles.

Rutherford model of the atom

Investigating the passage of a narrow beam of alpha particles through thin layers of matter, Rutherford found that most alpha particles pass through a metal foil consisting of many thousands of layers of atoms without deviating from the original direction, without experiencing scattering, as if there were no obstacles in their path. no obstacles. However, some particles were deflected at large angles, having experienced the action of large forces.

Based on the results of experiments to observe the scattering of alpha particles in matter Rutherford proposed a planetary model of the structure of the atom. According to this model the structure of the atom is similar to the structure of the solar system. At the center of each atom is positively charged nucleus with a radius of ≈ 10 -10 m, like planets, they circulate negatively charged electrons. Almost all the mass is concentrated in the atomic nucleus. Alpha particles can pass through thousands of layers of atoms without scattering, since most of the space inside atoms is empty, and collisions with light electrons have almost no effect on the motion of a heavy alpha particle. Scattering of alpha particles occurs in collisions with atomic nuclei.

Rutherford's model of the atom failed to explain all the properties of atoms.

According to the laws of classical physics, an atom consisting of a positively charged nucleus and electrons in circular orbits must radiate electromagnetic waves. The radiation of electromagnetic waves should lead to a decrease in the potential energy in the nucleus-electron system, to a gradual decrease in the radius of the electron orbit and the fall of the electron onto the nucleus. However, atoms usually do not emit electromagnetic waves, electrons do not fall on atomic nuclei, that is, atoms are stable.

Quantum postulates of N. Bohr

To explain the stability of atoms Niels Bohr proposed to abandon the usual classical ideas and laws when explaining the properties of atoms.

The basic properties of atoms receive a consistent qualitative explanation based on the adoption quantum postulates of N. Bohr.

1. The electron revolves around the nucleus only in strictly defined (stationary) circular orbits.

2. An atomic system can only be in certain stationary or quantum states, each of which corresponds to a certain energy E. An atom does not radiate energy in stationary states.

Stationary state of the atom from minimum stock energy is called main state, all other states are called excited (quantum) states. In the ground state, an atom can be infinitely long, the lifetime of an atom in an excited state lasts 10 -9 -10 -7 seconds.

3. Emission or absorption of energy occurs only when an atom passes from one stationary state to another. quantum energy electromagnetic radiation upon transition from a stationary state with energy E m into a state of energy E n is equal to the difference between the energies of an atom in two quantum states:

∆E = E m – E n = hv,

where v is the radiation frequency, h\u003d 2ph \u003d 6.62 ∙ 10 -34 J ∙ s.

Quantum model of the structure of the atom

In the future, some provisions of N. Bohr's theory were supplemented and rethought. The most significant change was the introduction of the concept of an electron cloud, which replaced the concept of an electron only as a particle. Later, Bohr's theory was replaced by quantum theory, which takes into account the wave properties of the electron and other elementary particles that form the atom.

basis modern theory atom structure is a planetary model, supplemented and improved. According to this theory, the nucleus of an atom consists of protons (positively charged particles) and neurons (uncharged particles). And around the nucleus, electrons (negatively charged particles) move along indefinite trajectories.

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The mass of electrons is several thousand times less than the mass of atoms. Since the atom as a whole is neutral, therefore, the bulk of the atom falls on its positively charged part.

For an experimental study of the distribution of a positive charge, and hence the mass inside the atom, Rutherford proposed in 1906 to apply the probing of the atom using α -particles. These particles arise from the decay of radium and some other elements. Their mass is about 8000 times the mass of the electron, and the positive charge is equal in modulus to twice the charge of the electron. These are nothing but fully ionized helium atoms. Speed α -particles is very large: it is 1/15 of the speed of light.

With these particles, Rutherford bombarded the atoms of heavy elements. Electrons, due to their small mass, cannot noticeably change the trajectory α -particles, like a pebble of several tens of grams in a collision with a car, are not able to noticeably change its speed. Scattering (changing direction of movement) α -particles can cause only the positively charged part of the atom. Thus, by scattering α -particles can determine the nature of the distribution of positive charge and mass inside the atom.

A radioactive preparation, such as radium, was placed inside lead cylinder 1, along which a narrow channel was drilled. bundle α -particles from the channel fell on thin foil 2 of the material under study (gold, copper, etc.). After scattering α -particles fell on a translucent screen 3 coated with zinc sulfide. The collision of each particle with the screen was accompanied by a flash of light (scintillation), which could be observed in a microscope 4. The entire device was placed in a vessel from which the air was evacuated.

With a good vacuum inside the device, in the absence of foil, a bright circle appeared on the screen, consisting of scintillations caused by a thin beam α -particles. But when foil was placed in the path of the beam, α -particles due to scattering were distributed on the screen in a circle larger area. Modifying the experimental setup, Rutherford tried to detect the deviation α -particles at large angles. Quite unexpectedly, it turned out that a small number α -particles (about one in two thousand) deviated at angles greater than 90°. Later, Rutherford admitted that, having offered his students an experiment to observe the scattering α -particles at large angles, he himself did not believe in a positive result. "It's almost as incredible," Rutherford said, "as if you fired a 15-inch projectile at a piece of thin paper, and the projectile came back to you and hit you." Indeed, it was impossible to predict this result on the basis of the Thomson model. When distributed throughout the atom, a positive charge cannot create a sufficiently intense electric field capable of throwing the a-particle back. Max Strength repulsion is determined by Coulomb's law:

where q α - charge α -particles; q is the positive charge of the atom; r is its radius; k - coefficient of proportionality. The electric field strength of a uniformly charged ball is maximum on the surface of the ball and decreases to zero as it approaches the center. Therefore, the smaller the radius r, the greater the repulsive force α -particles.

Determining the size of the atomic nucleus. Rutherford realized that α -particle could be thrown back only if the positive charge of the atom and its mass are concentrated in a very small region of space. So Rutherford came up with the idea of ​​the atomic nucleus - a body of small size, in which almost all the mass and all the positive charge of the atom are concentrated.

Planetary model of the atom, or Rutherford model, - the historical model of the structure of the atom, which was proposed by Ernest Rutherford as a result of an experiment with the scattering of alpha particles. According to this model, the atom consists of a small positively charged nucleus, which contains almost all the mass of the atom, around which the 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 motion of electrons is of a quantum nature and is not described by the laws of classical mechanics. Historically, Rutherford's planetary model replaced Joseph John Thomson's "plum pudding model", which postulates that negatively charged electrons are placed inside a positively charged atom.