Rutherford's classical model of the atom. Rutherford's experiments

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 were 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 surrounding bodies consist of tiny particles was made back in ancient times. Thinkers of that time imagined the atom as the smallest and indivisible particle of any substance. They argued that there is nothing in the Universe smaller in size than an atom. Such views were held by the great ancient Greek scientists and philosophers - Democritus, Lucretius, Epicurus. The hypotheses of these thinkers are today 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 in 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 bright minds of that time had the idea of ​​​​the indivisibility of the atom, which came from antiquity.

Studies of 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 of their internal structure remained open. The end of the 18th century was marked by such a significant event in the 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 curtain on 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 scientists during this period prepared fertile ground for the discoveries of the 20th century.

Thomson's experiments

English physicist John Thomson proved in 1897 that atoms contain electrons with a negative charge. At this stage, the false ideas that the atom is the limit of divisibility of any substance were completely destroyed. How did Thomson manage to prove the existence of electrons? In his experiments, the scientist placed electrodes in highly rarefied gases and passed an electric current. As a result, cathode rays appeared. Thomson carefully studied their features and discovered that they are a stream of charged particles that move at enormous speed. The scientist was able to calculate the mass of these particles and their charge. He also found out that they cannot be converted into neutral particles, since electric charge is the basis of their nature. So Thomson was also the creator of the world's first model of the structure of the atom. According to it, 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. John Thomson's experiments 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 was unable 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 the atom contained particles that were positively charged. Rutherford saw that when rays passed through a gas or through a thin metal plate, a small number of particles sharply deviated from the trajectory of motion. They were literally thrown back. The scientist guessed that this behavior was explained by collisions with positively charged particles. Such experiments allowed the physicist to create a model of the structure of the Rutherford atom.

Planetary model

Now the scientist’s ideas were somewhat different from the assumptions made by John Thomson. Their atomic models also became different. allowed him to create a completely new theory in this area. The scientist's discoveries were crucial for the further development of physics. Rutherford's model describes an atom as having a nucleus located at 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 scientist’s discovery helped explain the reason for the deflection 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, Rutherford's model, in which the atom moves around the nucleus in an orbit, was called planetary.

Works of Niels Bohr

Two years later, Danish physicist Niels Bohr tried to combine ideas about the structure of the atom with the quantum properties of light. The scientist used Rutherford's nuclear model of the atom as the basis for his new theory. According to Bohr, atoms rotate around the nucleus in circular orbits. This 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 expenditure of energy to maintain the spatial electromagnetic field arising from 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 intra-atomic conditions. Therefore, the scientist set himself the task of deducing new laws that would be valid in the world of 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 states that the atom has in which it does not change its energy, while the 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. Moreover, if an 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 made it possible to obtain an excellent explanation for the existence of a line spectrum. Around the same time, physicists Hertz and Frank, who lived in Germany, confirmed Niels Bohr's teaching about the existence of stationary, stable states of the atom and the possibility of changing the values ​​of atomic energy.

Collaboration between two scientists

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

Atomic structure

Units of charge, mass and energy in atomic physics.

So, the charge of any particle always contains an integer number of elementary charges. For a particle of atomic size, this integer number will also be small. In view of this, in atomic physics it is convenient to take the elementary charge e = 1.60 10-19 C as a unit of electric charge. In atomic physics, a unit of mass is taken to be 1/12 of the mass of an atom of the carbon isotope 12C. The atomic mass of this isotope is 12, and the molar mass M = 12 10-3 kg/mol. Therefore, the atomic mass unit (a.m.u.) is equal to

An atomic mass unit can also be defined as the mass of an atom of an element with atomic mass 1. Therefore, the mass of an atom (more precisely, its average value), expressed in atomic mass units, is equal to the atomic mass of the element.

Note that an element with an atomic mass equal to one does not exist in nature. The atomic mass of hydrogen is close to unity, but slightly greater: it is equal to 1.008. So, the mass of the lightest atom is 1.008 a. eat.

The unit of energy adopted in atomic physics is the energy acquired by a particle with charge e (for example, an electron) when passing through a potential difference of 1 V. This unit is called the electronvolt and is denoted eV. The energy acquired by a charge during movement in an electric field is equal to the product of the charge and the potential difference between the starting and ending points of the path, therefore
1 eV=1.6 10-19 C 1V=1.6 10-19J.
From the definition of electronvolt it follows that an electron accelerated by a potential difference U [V] has an energy numerically equal to U [eV]. An ion with a charge of 2e, having passed through the same potential difference, acquires an energy of 2U [eV], etc.

The energy of not only charged but also neutral particles can be measured in electronvolts. For example, let’s express in electron volts the energy of an oxygen atom (m=16 amu) moving at a speed v=103 m/s:

Units that are multiples of the electronvolt are also used:
1 keV=103 eV, 1 MeV=106 eV, 1 GeV=109 eV, 1 TeV=1012 eV.

Rutherford-Bohr model of the atom.

All matter consists of elementary particles. But matter does not consist directly of elementary particles. The building blocks or elements from which all matter is built are atoms. Until 1912, scientists represented the atom as a positively charged ball containing negatively charged electrons. The design, similar to a cupcake with electron raisins, was proposed by the Thomsons' namesakes, Joseph John and William Lord Kelvin.

In general, the positive and negative charges in such an atom are compensated and the atom is electrically neutral. It was assumed that the entire mass of an atom was concentrated in electrons. Since an electron is much lighter than an atom, even the simplest atoms must contain thousands of electrons.

In 1909, Rutherford commissioned the then young physicist Marsden to study the scattering of alpha rays as they passed through thin metal plates. Most elementary particles experienced minor deflections after passing through the plates. However, Marsden was able to detect very strongly deviated particles. True, there were very few of them, but it was surprising that they existed at all. Of course, Marsden might have imagined it. To register alpha particles, a spinthariscope was used - a small transparent screen coated with a special fluorescent substance. When an elementary particle hits such a screen, weak plowing occurs. The flash is very small and weak. It is observed under a microscope. For the eye to notice it, a person must get used to the darkness. To do this, before he starts working, that is, registering and counting flashes, he must sit for half an hour in complete darkness. It is natural, therefore, to assume that Marsden might have been mistaken.

Rutherford asks Marsden to repeat the experiments, but this time specifically monitor the particles that have received a large deviation up to 90°.

When, a few days later, Marsden entered Rutherford's office and said, “there are such particles,” Rutherford dropped the phone in surprise. Rutherford, although he suggested that Marsden conduct these experiments, did not himself expect such a result.

Rutherford later recalled: " it was the most incredible event of my life. It was almost as incredible as shooting a 15-inch shell at a piece of tissue paper and having the shell come back and hit you.".

The experiments were rechecked again, but this time Geiger joined the experiments. The phenomenon was experimentally studied and the experimental materials were published in the same year. However, the meaning of the results was mysterious. Thomson's atom could not stop an alpha particle flying at high speed.

In 1911, Rutherford published his article “The Scattering of Alpha and Beta Particles by Matter and the Structure of the Atom,” in which he proposed his famous planetary model of the atom.

A small, very massive positively charged nucleus, from which the alpha particle bounced in the experiments described, is located at the center of the Rutherford atom. Light negatively charged electrons revolve around the nucleus. Most of the space inside an atom is filled with emptiness. Overall, the model is very similar to our Solar System.

To Rutherford's great regret, the article was met with silence. Rutherford, of course, understood why. His atom was short-lived. An electron, rotating around a nucleus, must emit electromagnetic waves and lose energy as a result. At the same time, its speed would have to slow down, and it would have to fall onto the core. However, experience shows that almost all atoms in nature are stable.

Niels Bohr corrected the situation.

Bohr's theory

Bohr's postulates are similar in nature to Kepler's laws, of which there are also three. Both are guessed patterns obtained on the basis of experimental facts. It was perhaps even more difficult for Kepler. How, for example, can one arrive at the result that (formula)? Only after Newton formulated the laws of mechanics did Kepler's laws become possible to explain.

The main flaw in Rutherford's model was that an electron moving in a circular orbit around a nucleus should emit electromagnetic waves, but the evidence suggests that it does not. Scientists, including Rutherford, could not explain this contradiction. Bohr could not do this either. He simply sided with the facts: since electrons do not emit, then this is how it should be. This is how the first postulate appeared. In total, as we have already said, there are three of them.

Bohr's postulates

1. Electrons move in an atom in stationary orbits, while they do not emit or absorb energy.

2. Stationary orbits will be those for which the angular momentum of the electron mvr is equal to an integer multiple.

, where k = 1, 2, 3, 4...

3. When moving from one orbit to another, an electron emits or absorbs energy in the form of a photon.

Being in more distant orbits, an electron has more energy, therefore, moving to an orbit closer to the nucleus, it emits one photon with the energy

When an atom absorbs a photon, the electron can rise to a higher level.

Dimensions of a hydrogen atom

An electron, rotating around a nucleus, experiences a force of Coulomb attraction towards it:

where is the charge of the atomic nucleus with atomic number Z.

This force, in accordance with Newton’s second law, must be equal, therefore: or .

Bohr's second postulate tells us that the radius of the orbit cannot be arbitrary, but must obey the equation:

where we will denote the kth stationary orbit. From here we get

.

We have obtained the radius of the kth stationary orbit of an atom with serial number Z. For hydrogen Z=1. Let us find the radius of the first (k = 1) innermost orbit in which the electron has a minimum amount of energy.

Consequently, the diameter of the hydrogen atom is approximately , which is in good agreement with experimental data.

Let's find the energy of the electron in the kth orbit.

Its energy consists of the kinetic energy of motion in orbit and the potential electrostatic energy of interaction with the nucleus.

>> Structure of the atom. Rutherford's experiments

Chapter 12. ATOMIC PHYSICS

The discovery of the complex structure of the atom is the most important stage in the development of modern physics, which left its mark on all its further development. In the process of creating a quantitative theory of the structure of the atom, which made it possible to explain atomic spectra, new laws of motion of microparticles were discovered - the laws of quantum mechanics.

§ 93 STRUCTURE OF THE ATOM. RUTHERFORD'S EXPERIMENTS

Thomson's model. Scientists did not immediately come to the correct ideas about the structure of the atom. The first model of the atom was proposed by the English physicist J. J. Thomson, who discovered the electron. According to Thomson, the positive charge of an atom occupies the entire volume of the atom and is distributed in this volume with a constant density. The simplest atom - the hydrogen atom - is a positively charged ball with a radius of about 10 -8 cm, inside of which there is an electron. More complex atoms have several electrons in a positively charged ball, so that the atom is like a cupcake in which the electrons act as raisins.

However, Thomson's model of the atom turned out to be in complete contradiction with the properties of the atom already known by that time, the main one of which was stability.

Rutherford's experiments. 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’s mass is in its positively charged part.

To experimentally study the distribution of positive charge, and therefore mass, inside an atom, Ernest Rutherford proposed in 1906 to use probing of the atom using -particles. These particles arise from the decay of radium and some other elements. Their mass is approximately 8000 times the mass of an electron, and their positive charge is equal in magnitude to twice the electron charge. These are nothing more than fully ionized helium atoms. The speed of -particles is very high: it is 1/15 the speed of light.

Rutherford bombarded the atoms of heavy elements with these particles. Due to their low mass, electrons cannot noticeably change the trajectory of a particle, just as a pebble weighing several tens of grams when colliding with a car cannot significantly change its speed.

Rutherford Ernest (1871 - 1937)- great English physicist, native of New Zealand. With his experimental discoveries he laid the foundations of the modern doctrine of the structure of the atom and radioactivity. He was the first to study the composition of radioactive substances. He discovered the atomic nucleus and for the first time carried out the artificial transformation of atomic nuclei. All the experiments he carried out were of a fundamental nature and were distinguished by exceptional simplicity and clarity.

Scattering (change in direction of movement) of -particles can only be caused by the positively charged part of the atom. Thus, from the scattering of -particles, it is possible to determine the nature of the distribution of positive charge and mass inside the atom. The scheme of Rutherford's experiments is shown in Figure 12.1.

A radioactive drug, such as radium, was placed inside a lead cylinder l, along which a narrow channel was drilled. A beam of particles from the channel fell onto thin foil 2 made of the material under study (gold, copper, etc.). After scattering, the 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 through microscope 4. The entire device was placed in a vessel from which the air was evacuated.

With a good vacuum inside the device and in the absence of foil, a light circle appeared on the screen, consisting of scintillations caused by a thin beam of particles. But when foil was placed in the path of the beam, the particles, due to scattering, were distributed on the screen over a circle of a larger area.

By modifying the experimental setup, Rutherford tried to detect the deflection of β-particles at large angles. To do this, he surrounded the foil with scintillation screens and determined the number of flashes on each screen. Quite unexpectedly, it turned out that a small number of -particles (about one in two thousand) were deflected at angles greater than 90°. Rutherford later admitted that, having proposed to his students to conduct an experiment to observe the scattering of β-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 shell at a piece of tissue paper and the shell came back and hit you.”

In fact, it was impossible to predict this result on the basis of Thomson's model. When distributed throughout an atom, a positive charge cannot create a strong enough electric field to throw the particle back. The maximum repulsive force can be determined by Coulomb's law:

where q is the charge of the particle; q is the positive charge of the atom; R is its radius; k - proportionality coefficient. 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 force that repels the particles.

Determination of the size of the atomic nucleus.Rutherford realized that the -particle could be thrown back only if the positive charge of the atom and its mass were concentrated in a very small region of space. This is how Rutherford came to the idea of ​​the existence of an atomic nucleus - a small body in which almost all the mass and all the positive charge of the atom are concentrated.

Figure 12.2 shows the trajectories of alpha particles flying at various distances from the nucleus.

By counting the number of -particles scattered at different angles, Rutherford was able to estimate the size of the nucleus. It turned out that the core has a diameter of the order of 10 -12 -10 -13 cm (the diameters are different for different nuclei). The size of the atom itself is 10 -8 cm, i.e. 10-100 thousand times larger than the size of the nucleus. Subsequently, it was possible to determine the charge of the nucleus. Provided that the charge of the electron is taken as one, the charge of the nucleus is exactly equal to the number of a given chemical element in the periodic table of D.I. Mendeleev.

Planetary model of the atom. Based on his experiments, Rutherford created a planetary model of the atom. At the center of the atom is a positively charged nucleus, in which almost the entire mass of the atom is concentrated. In general, the atom is neutral. Therefore, the number of intra-atomic electrons, like the charge of the nucleus, is equal to the atomic number of the element in the periodic table. It is clear that electrons cannot be at rest inside an atom, since they would fall onto the nucleus. They move around the core, just as the planets orbit the Sun. This nature of electron motion is determined by the action of Coulomb attractive forces from the nucleus.

In a hydrogen atom, only one electron orbits the nucleus. The nucleus of a hydrogen atom has a positive charge equal in magnitude to the charge of an electron, and a mass approximately 1836.1 times greater than the mass of the electron. This nucleus was called a proton and began to be considered as an elementary particle. The size of a hydrogen atom is the radius of the orbit of its electron (Fig. 12.3).

A simple and visual planetary model of the atom has a direct experimental basis. It seems absolutely necessary to explain experiments on the scattering of -particles. But on the basis of this model it is impossible to explain the fact of the existence of an atom, its stability. After all, the movement of electrons in orbits occurs with acceleration, and quite considerable. According to Maxwell's laws of electrodynamics, an accelerating charge should emit electromagnetic waves with a frequency equal to the frequency of its revolution around the nucleus. Radiation is accompanied by a loss of energy. Losing energy, the electrons must approach the nucleus, just as a satellite approaches the Earth when braking in the upper layers of the atmosphere. As rigorous calculations based on Newtonian mechanics and Maxwellian electrodynamics show, an electron must fall onto the nucleus in a negligibly short time (about 10-8 s). The atom must cease to exist.

In reality, nothing like this happens. Atoms are stable and in an unexcited state can exist indefinitely, without emitting electromagnetic waves at all.

The conclusion, which is inconsistent with experience, about the inevitable death of the atom due to the loss of energy through radiation, is the result of applying the laws of classical physics to the phenomena occurring inside the atom. It follows that the laws of classical physics are not applicable to such phenomena.

Rutherford created a planetary model of the atom: electrons orbit around the nucleus, just as planets orbit around the Sun. This model is simple, justified experimentally, but does not explain the stability of the volume.

1. Why do negatively charged particles of an atom not have a noticeable effect on the scattering of -particles!

2. Why could not -particles be scattered at large angles if the positive charge of the atom was distributed throughout its entire volume!

3. Why the planetary model of the atom does not agree with the laws of classical physics!

Myakishev G. Ya., Physics. 11th grade: educational. for general education institutions: basic and profile. levels / G. Ya. Myakishev, B. V. Bukhovtsev, V. M. Charugin; edited by V. I. Nikolaeva, N. A. Parfentieva. - 17th ed., revised. and additional - M.: Education, 2008. - 399 p.: ill.

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The topic of this lesson is “Models of atoms. Rutherford's experience." Here we will learn how scientists studied the complex structure of atoms, how they found an explanation for this theory, and where the knowledge gained is applied today. We will also look at how Rutherford's experiment can be used to study the model of the atom.

In the previous lesson, we discussed that radioactivity produces different types of radiation: a-, b-, and g-rays. A tool appeared with which it was possible to study the structure of the atom.

After it became clear that the atom also has a complex structure, is somehow structured in a special way, it was necessary to investigate the very structure of the atom, explain how it is structured, what it consists of. And so scientists began this study.

The first ideas about the complex structure were expressed Thomson, who discovered the electron in 1897. In 1903, Thomson first proposed a model of the atom. According to Thomson's theory, the atom was a ball with a positive charge “smeared” throughout its entire volume. And inside, like floating elements, there were electrons. In general, according to Thomson, the atom was electrically neutral, that is, the charge of such an atom was equal to 0. The negative charges of the electrons compensated for the positive charge of the atom itself. The size of the atom was approximately 10 -10 m. Thomson's model was called “pudding with raisins”: the “pudding” itself is the positively charged “body” of the atom, and the “raisins” are the electrons (Fig. 1).

Rice. 1. Thomson's model of the atom (“raisin pudding”)

The first reliable experiment to determine the structure of the atom was carried out E. Rutherford. Today we know for sure that the atom is a structure reminiscent of a planetary solar system. At the center is a massive body around which the planets revolve. This model of the atom is called the planetary model.

Let's turn to Rutherford's experimental diagram (Fig. 2) and discuss the results that led to the creation of the planetary model.

Rice. 2. Scheme of Rutherford's experiment

Radium was placed inside a lead cylinder with a narrow hole. Using a diaphragm, a narrow beam of a-particles was created, which, flying through the opening of the diaphragm, hit a screen coated with a special composition; when hit, a micro-flash occurred. This glow when particles hit the screen is called a “scintillation flash.” Such flashes were observed on the surface of the screen using a microscope. Subsequently, as long as there was no gold plate in the circuit, all the particles that flew out of the cylinder hit one point. When a very thin gold plate was placed inside the screen in the path of flying a-particles, completely incomprehensible things began to be observed. As soon as the gold plate was placed, the a-particles began to deflect. Particles were noticed that deviated from their initial linear motion and already ended up at completely different points on this screen.

Moreover, when the screen was made almost closed, it turned out that there were particles that were somehow flying in the opposite direction. They deviate at an angle of 90° or more. These observations were analyzed by Rutherford, and the following rather interesting thing emerged.

First of all, Thomson's theory failed here. According to Thomson's theory, an atom is a ball 10 -10 m in size, in which the positive charge is smeared and there is an electron. So, electrons are very small particles; they cannot interfere with a-particles flying at a decent speed. The speed of a-particles in this case was about 10,000 km/s.

Imagine a situation where a truck collides with a toy car. It is clear that the truck will not even notice such a car. We can give this as an analogy of the collision of an electron with an a-particle. This means that it was necessary to conclude that the atom is structured differently, not as Thomson claimed. And, apparently, in the gold atom there is an object more massive than the a-particle, which has a positive charge.

Let's look at another picture that characterizes the scattering of a-particles on that massive particle, the presence of which Rutherford predicted in the atom (Fig. 3).

Rice. 3. Alpha particle scattering Based on the results of the experiments, it could be said that there is a massive positively charged object in the atom. An a-particle colliding with this large particle can be reflected back. Those particles that fly nearby are deflected at different angles. The farther an a-particle flies from this object, the smaller the angle they are deflected. This phenomenon is called " a-particle scattering».

Rutherford called the large particle that is inside an atom a nucleus. And he even appreciated its size. According to Rutherford, the size of the nucleus was 10 -14 -10 -15 m. This object was very, very small in size compared to an atom. The atom has a size of the order of 10 -10 m. Moreover, almost the entire mass of the atom was concentrated in the nucleus. And it is around the nucleus that electrons revolve.

this implies planetary model Rutherford, which states that the atom is a massive positively charged nucleus around which electrons revolve in their orbits (Fig. 4). In general, the atom is electrically neutral, that is, the charge of the atom is zero. If an atom has an excess or deficiency of electrons, it is called an ion.

Rice. 4. Planetary model of the atom

Of course, there were other theories of interest. Today, the generally accepted one, with some reservations, which we will discuss later, is the planetary model of the atom proposed by Ernest Rutherford.

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