In 1903, the English scientist Thomson proposed a model of the atom, which was jokingly called the "bun with raisins." According to him, an atom is a sphere with a uniform positive charge, in which negatively charged electrons are interspersed like raisins.
However, further studies of the atom showed that this theory is untenable. And a few years later, another English physicist, Rutherford, conducted a series of experiments. Based on the results, he built a hypothesis about the structure of the atom, which is still recognized worldwide.
Rutherford's experience: the proposal of his model of the atom
In his experiments, Rutherford passed a beam of alpha particles through thin gold foil. Gold was chosen for its plasticity, which made it possible to create a very thin foil, almost one layer of molecules thick. Behind the foil was a special screen that was illuminated when bombarded by alpha particles falling on it. According to Thomson's theory, alpha particles should have passed through the foil unhindered, deviating quite a bit to the sides. However, it turned out that some of the particles behaved in this way, and a very small part bounced back, as if hitting something.
That is, it was found that inside the atom there is something solid and small, from which alpha particles bounced off. It was then that Rutherford proposed a planetary model of the structure of the atom. Rutherford's planetary model of the atom explained the results of both his experiments and those of his colleagues. Not offered to date best model, although some aspects of this theory are still not consistent with practice in some very narrow areas of science. But basically, the planetary model of the atom is the most useful of all. What is this model?
Planetary model of the structure of the atom
As the name implies, an atom is compared to a planet. In this case, the planet is the nucleus of an atom. And electrons revolve around the nucleus at a fairly large distance, just like satellites revolve around the planet. Only the speed of rotation of electrons is hundreds of thousands of times greater than the speed of rotation of the fastest satellite. Therefore, during its rotation, the electron creates, as it were, a cloud above the surface of the nucleus. AND existing charges electrons are repelled by the same charges formed by other electrons around other nuclei. Therefore, the atoms do not "stick together", but are located at a certain distance from each other.
And when we talk about the collision of particles, we mean that they approach each other at a sufficiently large distance and are repelled by the fields of their charges. There is no direct contact. Particles in matter are generally very far apart. If by any means it were possible to implode together the particles of any body, it would be reduced by a billion times. The earth would become smaller than an apple. So the main volume of any substance, oddly enough it sounds, is occupied by a void in which charged particles are located, kept at a distance electronic forces interactions.
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 all the 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.
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
Bohr model of a hydrogen-like atom (Z nuclear charge), where a negatively charged electron is enclosed in an atomic shell surrounding a small, positively charged atomic nucleus ... Wikipedia
Model (French modèle, Italian modello, from Latin modulus measure, measure, sample, norm), 1) a sample that serves as a standard (standard) for serial or mass reproduction (M. of a car, M. of clothes, etc.). ), as well as the type, brand of any ... ...
I Model (Model) Walter (24.1.1891, Gentin, East Prussia, 21.4.1945, near Duisburg), fascist German General Field Marshal (1944). In the army since 1909, participated in the 1st World War of 1914 18. From November 1940 he commanded the 3rd tank ... ... Great Soviet Encyclopedia
STRUCTURE OF THE ATOM- (see) built from elementary particles 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
This term has other meanings, see Atom (meanings). Helium atom Atom (from other Greek ... Wikipedia
- (1871 1937), English physicist, one of the founders of the theory of radioactivity and the structure of the atom, founder of a scientific school, foreign corresponding member of the Russian Academy of Sciences (1922) and honorary member of the USSR Academy of Sciences (1925). Born in New Zealand, after graduating from ... ... encyclopedic Dictionary
Helium atom An atom (another Greek ἄτομος indivisible) is the smallest part of a chemical element, which is the carrier of its properties. An atom is made up of atomic nucleus and the surrounding electron cloud. The nucleus of an atom consists of positively charged protons and ... ... Wikipedia
Helium atom An 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
Books
- A set of tables. Physics. Grade 11 (15 tables), . Educational album of 15 sheets. Transformer. Electromagnetic induction in modern technology. Electronic lamps. Cathode-ray tube. Semiconductors. semiconductor diode. Transistor.…
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 all the 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 was small and a significant electric charge was concentrated in it. Rutherford's calculations showed that a scattering center, positively or negatively charged, must be at least 3000 times smaller than the size of an atom, which at that time was already known and estimated to be about 10 -10 m. Since electrons were already known at that time, and their mass and charge are determined, then the scattering center, which was later called the nucleus, must have had the 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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- Eise Eisingi Planetarium
- planetary fantasy
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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
Bohr model of the atom- Bohr model of a hydrogen-like atom (Z nucleus charge), where a negatively charged electron is enclosed in an atomic shell surrounding a small, positively charged atomic nucleus ... Wikipedia
Model (in science)- Model (French modèle, Italian modello, from Latin modulus measure, measure, sample, norm), 1) a sample that serves as a standard (standard) for serial or mass reproduction (M. car, M. clothes, etc. .), as well as the type, brand of any ... ...
Model- I Model (Model) Walter (January 24, 1891, Gentin, East Prussia, April 21, 1945, near Duisburg), Nazi German General Field Marshal (1944). In the army since 1909, participated in the 1st World War of 1914 18. From November 1940 he commanded the 3rd tank ... ... Great Soviet Encyclopedia
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
Atom- This term has other meanings, see Atom (meanings). Helium atom Atom (from other Greek ... Wikipedia
Rutherford Ernest- (1871 1937), English physicist, one of the founders of the theory of radioactivity and the structure of the atom, founder of a scientific school, foreign corresponding member of the Russian Academy of Sciences (1922) and honorary member of the USSR Academy of Sciences (1925). Born in New Zealand, after graduating from ... ... encyclopedic Dictionary
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
corpuscles- 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
Books
- A set of tables. Physics. Grade 11 (15 tables), . Educational album of 15 sheets. Transformer. Electromagnetic induction in modern technology. Electronic lamps. Cathode-ray tube. Semiconductors. semiconductor diode. Transistor.…
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 an electron, and positive charge is equal in modulus to twice the electron charge. 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 apparatus 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. The maximum repulsive force 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.
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 the 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, in general, the atom does not have 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 Nagaoka's ideas, although they have something in common with contemporary view about the atomic orbital.
None of the considered models (Fig. 7) explained how the properties chemical elements associated with the structure of their atoms.
Rice. 7. Some historical models 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 made a very important conclusion: the reason for the periodic change in the properties of chemical elements is associated with the features of the electronic structure of 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 when they pass through a 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 at 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 planets solar system 1 (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 oscillation frequency electromagnetic wave: Е = 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 the 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.
The planetary model, due to its visibility and Bohr's postulates, for a 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 a hypothesis that the electron has wave properties (the first principle 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 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 through mathematical functions and does not have a 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 the 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 loop with electric shock 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 the positive and negative value of the electron spin.
The "wave-faced model" (Fig. 10) is similar to the "ring-faced" model, 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 reflecting in a simplified form certain part 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 some time, but at a new, higher theoretical level: the Perrin and Kelvin models were developed in the Rutherford and Thomson models. 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).