thoughts about the nature of the surroundings began to visit humanity long before the heyday of modern civilization.First, people have speculated about the existence of some higher force, which they believed all being predetermined.But pretty soon, philosophers and clerics began to think about the fact of what, in fact, is the very fabric of existence.Theories have been set, but in historical perspective has become dominant atomic.
What is the atom in chemistry?This, as well as all related topics will be discussed in this article.We hope that in it you will find the answers to all your questions.
founder of the atomic theory
How to start the first lesson of chemistry?The structure of the atom - is the main theme.You might remember that the word "atom" is translated from Greek as "indivisible."Now, many historians believe that the first proposed the theory, some talk about the tiny particles that make up all things, Democritus.He lived in the fifth century BC.
unfortunately, this outstanding thinker virtually nothing is known.Has not reached us no written source of those times.And because of the ideas of the greatest scholars of his time, we have to learn only from the writings of Aristotle, Plato and other Greek thinkers.
So our theme - "The structure of the atom."In chemistry, not all had high ratings, but many remember that all the findings of the ancient scholars were built solely on inferences.Democritus was no exception.
How reasoned Democritus?
His logic was very simple, but at the same genius.Imagine that you have the sharpest knife in the world.You take an apple, for example, and then begin to cut it: on the two halves into quarters, divide them again ... In a word, sooner or later you will get a meager thickness of the slices, then what they have to share will be impossible.Here it is indivisible atom.In chemistry, this assertion is considered true almost until the end of the 19th century.
From Democritus to modern concepts
should be noted that from the ancient Greek ideas about the microworld survived only one word "atom".Now every schoolchild knows that the world around us is made up of much more fundamental and fine particles.In addition, from the perspective of modern science, the theory of Democritus was nothing more than a purely hypothetical computation is not supported by absolutely no evidence.However, in those days there were no electron microscopes, so to prove their case in other ways from the thinker would not have happened.
first suspicions that Democritus actually right there at the chemists.They quickly discovered that many substances in the course of the reactions break down into simpler components.In addition, it brought severe chemical regularities of these processes.So, they noticed that the water required for the eight mass fraction of oxygen and one - hydrogen (Avogadro's law).
In the Middle Ages, any materialistic doctrine, including the theory of Democritus, distribution and development could not get at all.And only in the XVIII century, scientists have once again returned to the atomic theory.By the time the chemist Lavoisier, our great Lomonosov and talented English physicist D. Dalton (which we will discuss separately), has convincingly demonstrated to their colleagues the reality of atoms.It should be stressed that even in the enlightened 18th century atomic theory for a long time many outstanding minds of that time seriously considered.
Whatever it was, but even the great scientists have not yet put forward theories about the structure of the atom, since he was considered one and indivisible particle, the basis of everything.
Unfortunately, chemical experiments could not clearly prove the reality of the transformation atoms of some substances into others.Yet the fundamental science in the study of the structure of atoms was precisely chemistry.Atoms and molecules have been studied for a long time, a brilliant Russian scientist, without which it is impossible to imagine modern science.
Doctrine Mendeleev
huge role in the development of the atomic doctrine played Mendeleev, who in 1869 created his brilliant periodic system.For the first time the scientific community was represented by a theory which not only rejected, but also reasonable complement all the assumptions of the materialists.Already in the 19th century, scientists were able to prove the existence of electrons.These findings led the best minds of the 20th century to seriously study the atom.In chemistry this time, it was also marked by a plurality of openings.
But the doctrine of the periodic valuable not only that.It is still unclear exactly how atoms are formed of various chemical elements.But the great Russian scientist was able to prove conclusively that they are all, without exception, are closely related to each other.
Opening Dalton
But to be able to interpret the multiple disparate data could only John Dalton, whose name is forever imprinted in the open his own law.Typically, only a scientist investigated the behavior of gases, but the range of interests he was much wider.In 1808 he began publishing his new fundamental work.
It Dalton suggested that each chemical element has a specific atom.But scientists, like Democritus many centuries before him, still believed that they are completely inseparable.In its many drafts diagrammatic drawings, in which atoms are presented in the form of simple pellets.This idea originated more than 2,500 years ago, lasted almost to the present day!However, only relatively recently it has been discovered really deep structure of the atom.Chemistry (Grade 9 in particular) even today is largely guided by the ideas that were first voiced in the 18th century.
Experimental confirmation of the divisibility of atoms
However, until the end of the 19th century almost all scientists believed that the atom - the limit beyond which there is nothing.They thought that the basis of all creation is exactly it.This was facilitated by a variety of experiments: anyway, but changes only the molecule, while the rate with the atoms of the material did not occur absolutely nothing that could not be explained simply chemistry.The structure of carbon atoms, for example, remains completely unchanged even in different allotropic states.
In short, for a long time there was absolutely no experimental data that even indirectly confirmed the suspicions of some scientists that there are some more fundamental particles.Only in the 19th century (not least thanks to the experience Curies) it was shown that under certain conditions the atoms of one element can be transformed into the other.These findings formed the basis of modern ideas about the world around us.
Raisins and puddings
In 1897, George. Thomson, English physicist, it was found that any atom has a certain amount of negatively charged particles, which he called the "electronic".Already in 1904, the scientist created the first atomic model, which is better known under the designation "plum pudding".The name is quite accurately reflects the essence.According to Thomson's theory, the atom in chemistry - is a "vessel" with uniformly distributed therein charge and electrons.
Note that this model was in circulation even in the 20th century.Later it turned out that it was absolutely wrong.Still, it was the first deliberate attempt to man (and on a scientific basis) to recreate the surrounding microcosm, offering a model of the atom, quite simple and clear.
experiments Curie
It is believed that the couple Pierre and Marie Curie marked the beginning of atomic physics.Of course, the contribution of these men of genius, actually sacrificed their health and life can not be underestimated, but their experiences were far more fundamental.Almost simultaneously with Rutherford they proved that an atom - is much more complex and heterogeneous structure.The phenomenon of radioactivity, they investigated it and talked about it.
At the beginning of 1898 Marie published the first article devoted to radiation.Soon, Marie and Pierre Curie have shown that a mixture of chlorides of uranium and radium are beginning to emerge other substances, which doubted the existence of the official chemistry.The structure of the atom has since begun to explore in earnest.
«Planetary" approach
finally decided to make Rutherford bombarded atoms of heavy metals α-particles (fully ionized helium).The scientist immediately suggested that light electrons can not be able to change the trajectory of the particles.Accordingly, the dispersion may cause only some heavier components that may be contained in the nucleus of the atom.Immediately, we note that the original Rutherford did not claim to change the theory of the "pudding".This model of the atom was considered impeccable.
Therefore result that almost all particles with no problems took place through a thin layer of silver, he was not surprised.That's just it soon became clear that some of the helium atoms were deflected just 30 °.It was not what they said at the time chemistry.The composition of the atom by Thomson assumed uniform distribution of electrons.But this is clearly contrary to the observed phenomena.
extremely rare, but some particles flew at an angle, even 180 °.Rutherford was in deep perplexity.It is sharply contradicted the "pudding", a charge which was supposed to be (according to Thomson's theory) is distributed evenly.Therefore, unevenly charged sites that would repel the ionized helium, were absent.
What conclusions came to Rutherford?
These circumstances prompted scientists to think that the atom is almost empty and only the center focus some education with a positive charge - the kernel.So there was the planetary model of the atom, which postulates the following:
- As we have already said, in the central part of the kernel is located, and its volume (relative to the size of the atom itself) is negligible.
- Almost all atomic mass, as well as all the positive charge are found in the nucleus.
- electrons revolve around him.It is important that their number is equal to the positive charge.
Paradoxes theory
Everything was good, but the model of the atom does not explain their incredible resilience.It should be remembered that the electrons move in orbits with great acceleration.By all the laws of electrodynamics an object over time, should lose its charge.If you take into account the postulates of Newton and Maxwell, the electrons have all crumble to the core, like hail on the ground.
Of course, in reality, nothing happens.Every atom is not only quite resistant, but can be quite indefinitely, with no radiation from it will not go.This discrepancy is explained by the fact that to the microworld we try to apply the laws, which are valid only in respect of classical mechanics.They, as it turned out, to the phenomena of the atomic scale do not apply at all.And because of the atom (Chemistry, Grade 11) textbook authors try to explain as much as possible in simple words.
Doctrine
Bohr, Danish physicist Niels Bohr has been proven that in the microcosm can not be subject to the same laws, regulations which are valid for macroscopic objects.It was his idea that the microcosm of "guided" solely by quantum laws.Of course, then there was no quantum theory itself, but Bohr actually became its forefather, expressing his thoughts in the form of three postulates that "saved" atom bound to be killed if he "lived" according to the theory of Rutherford.It is this theory Dane became the basis of quantum mechanics all.
Bohr's postulates
- first one reads any atomic system can be located only in specific nuclear states, and each of them is characterized by a definite value of energy (E).If the stationary state of the atom (quiet), then it can not radiate.
- second postulate suggests that the emission of light energy occurs only when a transition from a higher energy in a more moderate.Accordingly, the energy released is equal to the difference value between two stationary states.
atomic model of Niels Bohr
This semiclassical theory scientist proposed in 1913.It is noteworthy that in its foundation he laid planetary model of Rutherford, who shortly before he described the atom of matter.We have already said that contrary to classical mechanics calculations Rutherford: on the basis of it, it was assumed that with time the electron was sure to fall on the surface of the atom.
to "bypass" this contradiction, the scientist has introduced a special admission.Its essence lies in the fact that radiate energy (that was to lead to their downfall) electrons can only moving in any particular orbits.At movement of the other paths alleged chemical atoms remain in a passive state.According to Bohr's theory such orbits are those quantitative point movement which was equal to Planck's constant.
quantum theory of atomic structure
As we have said, today in the course of the quantum theory of atomic structure.Chemistry recent years guided solely by her.It is based on four fundamental axioms.
1. First, the duality (wave-particle nature) of the electron.Simply put, it behaves this particle, and as a material object (corpuscle), and as a wave.As it has a specific particle charge and mass.The ability of the electrons to the diffraction in common with classical waves.The length of the wave itself (λ) and the particle velocity (v) can be connected to each other by special de Broglie relation: λ = h / mv.As you might guess, m - mass of the electron.
2. coordinates and velocities of the particles to measure with absolute precision is absolutely impossible.The more accurately determine the coordinates, the greater the uncertainty in the speed.As, however, and vice versa.This phenomenon is called the Heisenberg uncertainty which can be expressed as the following equation: Δx ∙ m ∙ Δv & gt;ћ / 2.Delta X (△ x) expresses the uncertainty of the position coordinates in space.Accordingly, the delta V (Δv) displays the speed error.
3. Contrary to previous popular belief, the electrons do not pass through the strictly defined orbits, like a train on rails.Quantum theory says that an electron can be anywhere in space, but the probability of this is different for each segment.
That part of the space directly around the atomic nucleus in which the probability is maximum, called orbitals.Modern chemistry structure of electron shells of atoms studies from this point of view.Of course, the schools are taught the proper distribution of the electrons through the levels, but, apparently, in reality they differ quite differently.
4. The nucleus of an atom consists of nucleons (protons and neutrons).The serial number of the element in the periodic table indicates the number of protons in its nucleus, and the sum of protons and neutrons is equal to the atomic mass.That explains the structure of the atomic nucleus of modern chemistry.
founders of quantum mechanics
note the scientists who made the greatest contribution to the development of this important sector: the French physicist Louis de Broglie, Heisenberg German, Austrian, Schrodinger, the Englishman Dirac.All of these people were later awarded the Nobel Prize.
How far in this plan went chemistry?The structure of the atom, most of those years chemists believed simple enough: many only in 1947 finally recognized the reality of the existence of elementary particles.
Some conclusions
Generally, when you create a quantum theory has not been without mathematicians, since all of these processes can only be calculated using complex calculations.But the main difficulty is not the point.Those processes, which are described by this theory, available not only to our senses, for all the modern scientific technology, but also imagination.
No one even approximately can not imagine the processes in microcosm, as they did not like all the phenomena that we observe in the macrocosm.Just think: the latest discoveries give reason to assume that the quarks, neutrinos and other fundamental particles exist in the nine (!) Dimension.
