An atom is the smallest particle of a chemical substance that can retain its properties. The word "atom" comes from the ancient Greek "atomos", meaning "indivisible". Depending on how many and what particles are in an atom, a chemical element can be determined.
Briefly about the structure of the atom
How can you briefly list the basic information about is a particle with one nucleus, which is positively charged. Around this nucleus is a negatively charged cloud of electrons. Each atom in its normal state is neutral. The size of this particle can be entirely determined by the size of the electron cloud that surrounds the nucleus.
The nucleus itself, in turn, also consists of smaller particles - protons and neutrons. Protons are positively charged. Neutrons do not carry any charge. However, protons and neutrons are combined into one category and are called nucleons. If basic information about the structure of the atom is needed briefly, then this information can be limited to the listed data.
First information about the atom
The ancient Greeks suspected that matter could consist of small particles. They believed that everything that exists is made of atoms. However, such a view was purely philosophical in nature and cannot be interpreted scientifically.
The first to obtain basic information about the structure of the atom was an English scientist. It was this researcher who was able to discover that two chemical elements can enter into different ratios, and each such combination will represent a new substance. For example, eight parts of the element oxygen give rise to carbon dioxide. Four parts oxygen is carbon monoxide.
In 1803, Dalton discovered the so-called law of multiple ratios in chemistry. Using indirect measurements (since not a single atom could then be examined under the microscopes of that time), Dalton made a conclusion about the relative weight of atoms.
Rutherford's research
Almost a century later, basic information about the structure of atoms was confirmed by another English chemist - the Scientist proposed a model of the electron shell of the smallest particles.
At that time, Rutherford's "Planetary Model of the Atom" was one of the most important steps that chemistry could take. Basic information about the structure of the atom indicated that it was similar to the solar system: electron particles rotate around the nucleus in strictly defined orbits, just as planets do.
Electronic shell of atoms and formulas of atoms of chemical elements
The electron shell of each atom contains exactly as many electrons as there are protons in its nucleus. This is why the atom is neutral. In 1913, another scientist obtained basic information about the structure of the atom. Niels Bohr's formula was similar to that obtained by Rutherford. According to his concept, electrons also revolve around the nucleus located at the center. Bohr refined Rutherford's theory and brought harmony to its facts.
Even then, formulas for some chemical substances were compiled. For example, schematically the structure of the nitrogen atom is denoted as 1s 2 2s 2 2p 3, the structure of the sodium atom is expressed by the formula 1s 2 2s 2 2p 6 3s 1. Through these formulas you can see how many electrons move in each of the orbitals of a particular chemical substance.
Schrödinger model
However, later this atomic model also became outdated. Basic information about the structure of the atom, known to science today, largely became available thanks to the research of the Austrian physicist
He proposed a new model of its structure - a wave model. By this time, scientists had already proven that the electron is endowed not only with the nature of a particle, but also has the properties of a wave.
However, the Schrödinger and Rutherford model also has general provisions. Their theories are similar in that electrons exist at certain levels.
Such levels are also called electronic layers. Using the level number, the electron energy can be characterized. The higher the layer, the more energy it has. All levels are counted from bottom to top, so the level number corresponds to its energy. Each of the layers in the electron shell of an atom has its own sublevels. In this case, the first level may have one sublevel, the second - two, the third - three, and so on (see the above electronic formulas for nitrogen and sodium).
Even smaller particles
At the moment, of course, even smaller particles have been discovered than the electron, proton and neutron. It is known that the proton consists of quarks. There are even smaller particles of the universe - for example, the neutrino, which is a hundred times smaller in size than a quark and a billion times smaller than a proton.
A neutrino is such a small particle that it is 10 septillion times smaller than, for example, a tyrannosaurus rex. The tyrannosaurus itself is as many times smaller in size than the entire observable Universe.
Basic information about the structure of the atom: radioactivity
It has always been known that no chemical reaction can transform one element into another. But in the process of radioactive radiation this happens spontaneously.
Radioactivity is the ability of atomic nuclei to transform into other nuclei - more stable ones. When people received basic information about the structure of atoms, isotopes, to a certain extent, could serve as the embodiment of the dreams of medieval alchemists.
As isotopes decay, radioactive radiation is emitted. This phenomenon was first discovered by Becquerel. The main type of radioactive radiation is alpha decay. When it occurs, an alpha particle is released. There is also beta decay, in which a beta particle is ejected from the nucleus of an atom.
Natural and artificial isotopes
Currently, about 40 natural isotopes are known. Most of them are located in three categories: uranium-radium, thorium and actinium. All these isotopes can be found in nature - in rocks, soil, air. But besides them, about a thousand artificially derived isotopes are also known, which are produced in nuclear reactors. Many of these isotopes are used in medicine, especially in diagnostics..
Proportions within an atom
If we imagine an atom whose dimensions are comparable to the dimensions of an international sports stadium, then we can visually obtain the following proportions. The electrons of an atom in such a “stadium” will be located at the very top of the stands. Each one will be smaller than the head of a pin. Then the core will be located in the center of this field, and its size will be no larger than the size of a pea.
Sometimes people ask what an atom actually looks like. In fact, it literally does not look like anything - not for the reason that the microscopes used in science are not good enough. The dimensions of an atom are in those areas where the concept of “visibility” simply does not exist.
Atoms are very small in size. But how small are these sizes really? The fact is that the smallest grain of salt, barely visible to the human eye, contains about one quintillion atoms.
If we imagine an atom of such a size that could fit in a human hand, then next to it there would be viruses 300 meters long. Bacteria would be 3 km long, and the thickness of a human hair would be 150 km. In a supine position, he would be able to go beyond the boundaries of the earth's atmosphere. And if such proportions were valid, then a human hair could reach the Moon in length. This is such a complex and interesting atom, which scientists continue to study to this day.
> How many atoms are there in the Universe?
Find out, how many atoms are in the universe: how it was calculated, the size of the visible Universe, the history of birth and development with photos, the number of stars, mass, research.
Surely everyone knows that the Universe is a large-scale place. According to general estimates, only 93 billion light years open before us (“Visible Universe”). This is a huge number, especially if we do not forget that this is only the part that is accessible to our devices. And, given such volumes, it would not be strange to assume that the amount of the substance should also be significant.
It is interesting to start studying the issue on a tiny scale. After all, our Universe contains 120-300 sextillion stars (1.2 or 3 x 10 23). If we increase everything to the atomic level, then these numbers seem simply unthinkable. How many atoms are there in the Universe?
According to calculations, it turns out that the Universe is filled with 10 78 -10 82 atoms. But even these indicators do not reflect exactly how much substance it contains. It was mentioned above that we can comprehend 46 billion light years in any direction, which means that we cannot see the whole picture. In addition, the Universe is constantly expanding, which moves objects away from us.
Not long ago, a German supercomputer produced a result indicating that there are 500 billion galaxies in sight. If we turn to conservative sources, we get 300 billion. One galaxy can accommodate 400 billion stars, so the total number in the Universe can reach 1.2 x 10 23 – 100 sextillion.
The average weight of a star is 10 35 grams. Total weight – 10 58 grams. Calculations show that each gram contains 10 24 protons or the same number of hydrogen atoms (one hydrogen contains one proton). In total we get 10 82 hydrogen.
We take the visible Universe as a basis, within which this amount should be distributed evenly (over 300 million light years). But on a smaller scale, matter will create clumps of luminous matter, which we all know about.
To summarize, most of the atoms of the Universe are concentrated in stars, creating galaxies, which unite into clusters, which in turn form superclusters and complete all this with the formation of the Great Wall. This is with magnification. If you go in the opposite direction and take a smaller scale, then the clusters are filled with clouds with dust, gas and other matter.
Matter tends to spread isotropically. That is, all celestial areas are the same and each contains the same amount. Space is saturated with a wave of powerful isotropic radiation, equated to 2.725 K (slightly above absolute zero).
The cosmological principle states about a homogeneous Universe. Based on it, it can be argued that the laws of physics will be equally valid anywhere in the Universe and should not be violated on a large scale. This idea is also fueled by observations demonstrating the evolution of the universe's structure after the Big Bang.
Researchers agree that most matter was formed at the time of the Big Bang, and expansion does not add new matter. The mechanisms of the last 13.7 billion years are expansion and dispersion of the main masses.
But the theory is complicated by Einstein's mass-energy equivalence, which emerges from general relativity (adding mass gradually increases the amount of energy).
However, the density of the Universe remains stable. Modern reaches 9.9 x 10 30 grams per cm 3. 68.3% of dark energy, 26.8% of dark matter and 4.9% of luminous matter are concentrated here. It turns out that the density is one hydrogen atom per 4 m 3.
Scientists still cannot decipher the properties, so it is impossible to say for sure whether they are distributed evenly or form dense clumps. But it is believed that dark matter slows down expansion, but dark energy accelerates it.
All numbers given regarding the number of atoms in the Universe are rough estimates. Don't forget the main idea: we are talking about calculations of the visible Universe.
DEFINITION
Atom– the smallest chemical particle.
The variety of chemical compounds is due to the different combinations of atoms of chemical elements into molecules and non-molecular substances. The ability of an atom to enter into chemical compounds, its chemical and physical properties are determined by the structure of the atom. In this regard, for chemistry, the internal structure of the atom and, first of all, the structure of its electronic shell are of paramount importance.
Atomic structure models
At the beginning of the 19th century, D. Dalton revived the atomic theory, relying on the fundamental laws of chemistry known by that time (constancy of composition, multiple ratios and equivalents). The first experiments were carried out to study the structure of matter. However, despite the discoveries made (atoms of the same element have the same properties, and atoms of other elements have different properties, the concept of atomic mass was introduced), the atom was considered indivisible.
After obtaining experimental evidence (late 19th - early 20th century) of the complexity of the structure of the atom (photoelectric effect, cathode and x-rays, radioactivity), it was found that the atom consists of negatively and positively charged particles that interact with each other.
These discoveries gave impetus to the creation of the first models of atomic structure. One of the first models was proposed J. Thomson(1904) (Fig. 1): the atom was imagined as a “sea of positive electricity” with electrons oscillating in it.
After experiments with α-particles, in 1911. Rutherford proposed the so-called planetary model atomic structure (Fig. 1), similar to the structure of the solar system. According to the planetary model, at the center of the atom there is a very small nucleus with a charge Z e, the dimensions of which are approximately 1,000,000 times smaller than the dimensions of the atom itself. The nucleus contains almost the entire mass of the atom and has a positive charge. Electrons move around the nucleus in orbits, the number of which is determined by the charge of the nucleus. The external trajectory of the electrons determines the external dimensions of the atom. The diameter of an atom is 10 -8 cm, while the diameter of the nucleus is much smaller -10 -12 cm.
Rice. 1 Models of atomic structure according to Thomson and Rutherford
Experiments on studying atomic spectra have shown the imperfection of the planetary model of the structure of the atom, since this model contradicts the line structure of atomic spectra. Based on Rutherford's model, Einstein's doctrine of light quanta and Planck's quantum theory of radiation Niels Bohr (1913) formulated postulates, which consists theory of atomic structure(Fig. 2): an electron can rotate around the nucleus not in any, but only in some specific orbits (stationary), moving along such an orbit it does not emit electromagnetic energy, radiation (absorption or emission of a quantum of electromagnetic energy) occurs during a transition (jump-like) electron from one orbit to another.
Rice. 2. Model of the structure of the atom according to N. Bohr
The accumulated experimental material characterizing the structure of the atom has shown that the properties of electrons, as well as other micro-objects, cannot be described on the basis of the concepts of classical mechanics. Microparticles obey the laws of quantum mechanics, which became the basis for the creation modern model of atomic structure.
The main theses of quantum mechanics:
- energy is emitted and absorbed by bodies in separate portions - quanta, therefore, the energy of particles changes abruptly;
- electrons and other microparticles have a dual nature - they exhibit the properties of both particles and waves (wave-particle duality);
— quantum mechanics denies the presence of certain orbits for microparticles (for moving electrons it is impossible to determine the exact position, since they move in space near the nucleus, you can only determine the probability of finding an electron in different parts of space).
The space near the nucleus in which the probability of finding an electron is quite high (90%) is called orbital.
Quantum numbers. Pauli's principle. Klechkovsky's rules
The state of an electron in an atom can be described using four quantum numbers.
n– main quantum number. Characterizes the total energy reserve of an electron in an atom and the number of the energy level. n takes on integer values from 1 to ∞. The electron has the lowest energy when n=1; with increasing n – energy. The state of an atom when its electrons are at such energy levels that their total energy is minimal is called ground state. States with higher values are called excited. Energy levels are indicated by Arabic numerals according to the value of n. Electrons can be arranged in seven levels, therefore, n actually exists from 1 to 7. The main quantum number determines the size of the electron cloud and determines the average radius of an electron in an atom.
l– orbital quantum number. Characterizes the energy reserve of electrons in the sublevel and the shape of the orbital (Table 1). Accepts integer values from 0 to n-1. l depends on n. If n=1, then l=0, which means that there is a 1st sublevel at the 1st level.
m e– magnetic quantum number. Characterizes the orientation of the orbital in space. Accepts integer values from –l through 0 to +l. Thus, when l=1 (p-orbital), m e takes on the values -1, 0, 1 and the orientation of the orbital can be different (Fig. 3).
Rice. 3. One of the possible orientations in space of the p-orbital
s– spin quantum number. Characterizes the electron's own rotation around its axis. Accepts values -1/2(↓) and +1/2(). Two electrons in the same orbital have antiparallel spins.
The state of electrons in atoms is determined Pauli principle: an atom cannot have two electrons with the same set of all quantum numbers. The sequence of filling the orbitals with electrons is determined Klechkovsky rules: the orbitals are filled with electrons in increasing order of the sum (n+l) for these orbitals, if the sum (n+l) is the same, then the orbital with the smaller n value is filled first.
However, an atom usually contains not one, but several electrons, and to take into account their interaction with each other, the concept of effective nuclear charge is used - an electron in the outer level is subject to a charge that is less than the charge of the nucleus, as a result of which the internal electrons screen the external ones.
Basic characteristics of an atom: atomic radius (covalent, metallic, van der Waals, ionic), electron affinity, ionization potential, magnetic moment.
Electronic formulas of atoms
All the electrons of an atom form its electron shell. The structure of the electron shell is depicted electronic formula, which shows the distribution of electrons across energy levels and sublevels. The number of electrons in a sublevel is indicated by a number, which is written to the upper right of the letter indicating the sublevel. For example, a hydrogen atom has one electron, which is located in the s-sublevel of the 1st energy level: 1s 1. The electronic formula of helium containing two electrons is written as follows: 1s 2.
For elements of the second period, electrons fill the 2nd energy level, which can contain no more than 8 electrons. First, electrons fill the s-sublevel, then the p-sublevel. For example:
5 B 1s 2 2s 2 2p 1
Relationship between the electronic structure of the atom and the position of the element in the Periodic Table
The electronic formula of an element is determined by its position in the Periodic Table D.I. Mendeleev. Thus, the period number corresponds to In elements of the second period, electrons fill the 2nd energy level, which can contain no more than 8 electrons. First, electrons fill In elements of the second period, electrons fill the 2nd energy level, which can contain no more than 8 electrons. First, electrons fill the s-sublevel, then the p-sublevel. For example:
5 B 1s 2 2s 2 2p 1
In atoms of some elements, the phenomenon of electron “leap” from the outer energy level to the penultimate one is observed. Electron leakage occurs in atoms of copper, chromium, palladium and some other elements. For example:
24 Cr 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1
an energy level that can contain no more than 8 electrons. First, electrons fill the s-sublevel, then the p-sublevel. For example:
5 B 1s 2 2s 2 2p 1
The group number for elements of the main subgroups is equal to the number of electrons in the outer energy level; such electrons are called valence electrons (they participate in the formation of a chemical bond). Valence electrons for elements of side subgroups can be electrons of the outer energy level and the d-sublevel of the penultimate level. The group number of elements of secondary subgroups III-VII groups, as well as for Fe, Ru, Os, corresponds to the total number of electrons in the s-sublevel of the outer energy level and the d-sublevel of the penultimate level
Tasks:
Draw the electronic formulas of the phosphorus, rubidium and zirconium atoms. Indicate the valence electrons.
Answer:
15 P 1s 2 2s 2 2p 6 3s 2 3p 3 Valence electrons 3s 2 3p 3
37 Rb 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 5s 1 Valence electrons 5s 1
40 Zr 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 2 5s 2 Valence electrons 4d 2 5s 2
The desire for a state with the lowest energy is a general property of matter. You probably know about mountain avalanches and rockfalls. Their energy is so great that it can sweep away bridges, houses and other large and durable structures. The reason for this formidable natural phenomenon is that the mass of snow or stones tends to occupy the state with the lowest energy, and the potential energy of the physical body at the foot of the mountain is less than at the slope or top.
Atoms form bonds with each other for the same reason: the total energy of connected atoms is less than the energy of the same atoms in a free state. This is a very happy circumstance for you and me - after all, if there was no gain in energy when combining atoms into molecules, then the Universe would be filled only with atoms of elements, and the appearance of simple and complex molecules necessary for the existence of life would be impossible.
However, atoms cannot bond with each other randomly. Each atom is capable of bonding with a specific number of other atoms, and the bonded atoms are located in space in a strictly defined manner. The reason for these limitations should be sought in the properties of the electron shells of atoms, or more precisely, in the properties external electron shells with which atoms interact with each other.
The completed outer electron shell has less (i.e., more favorable for the atom) energy than the incomplete one. According to the octet rule, a completed shell contains 8 electrons:
These are the outer electron shells of noble gas atoms, with the exception of helium (n = 1) , whose complete shell consists of two s electrons (1s 2 ) just because p -there is no sublevel at the 1st level.
The outer shells of all elements, except for noble gases, are INCOMPLETE and in the process of chemical interaction they are COMPLETED whenever possible.
For such “completion” to occur, the atoms must either transfer electrons to each other or make them available for common use. This forces the atoms to be close to each other, i.e. be linked by a chemical bond.
There are several terms for types of chemical bonding: covalent, polar covalent, ionic, metallic, donor-acceptor, hydrogen and some others. However, as we will see, all methods of binding particles of matter to each other have a common nature - this is the provision of their own electrons for common use (more strictly - socialization electrons), which is often supplemented by electrostatic interaction between unlike charges that arise during electron transitions. Sometimes the forces of attraction between individual particles can be purely electrostatic. This is not only the attraction between ions, but also various intermolecular interactions.
In the process of the development of science, chemistry was faced with the problem of calculating the amount of substance for carrying out reactions and the substances obtained in their course.
Today, for such calculations of chemical reactions between substances and mixtures, the value of the relative atomic mass included in the periodic table of chemical elements by D. I. Mendeleev is used.
Chemical processes and the influence of the proportion of an element in substances on the course of the reaction
Modern science, by the definition of “relative atomic mass of a chemical element,” means how many times the mass of an atom of a given chemical element is greater than one twelfth of a carbon atom.
With the advent of the era of chemistry, the need for precise determinations of the course of a chemical reaction and its results grew.
Therefore, chemists constantly tried to solve the problem of the exact masses of interacting elements in a substance. One of the best solutions at that time was to bind to the lightest element. And the weight of its atom was taken as one.
The historical course of counting matter
Hydrogen was initially used, then oxygen. But this method of calculation turned out to be inaccurate. The reason for this was the presence of isotopes with masses of 17 and 18 in oxygen.
Therefore, having a mixture of isotopes technically produced a number other than sixteen. Today, the relative atomic mass of an element is calculated based on the weight of the carbon atom taken as a basis, in a ratio of 1/12.
Dalton laid the foundations for the relative atomic mass of an element
Only some time later, in the 19th century, Dalton proposed to carry out calculations using the lightest chemical element - hydrogen. At lectures to his students, he demonstrated on figures carved from wood how atoms are connected. For other elements, he used data previously obtained by other scientists.
According to Lavoisier's experiments, water contains fifteen percent hydrogen and eighty-five percent oxygen. With this data, Dalton calculated that the relative atomic mass of the element that makes up water, in this case oxygen, is 5.67. The error in his calculations stems from the fact that he believed incorrectly regarding the number of hydrogen atoms in a water molecule.
In his opinion, there was one hydrogen atom for every oxygen atom. Using the data of the chemist Austin that ammonia contains 20 percent hydrogen and 80 percent nitrogen, he calculated the relative atomic mass of nitrogen. With this result, he came to an interesting conclusion. It turned out that the relative atomic mass (the formula of ammonia was mistakenly taken with one molecule of hydrogen and nitrogen) was four. In his calculations, the scientist relied on Mendeleev’s periodic system. According to the analysis, he calculated that the relative atomic mass of carbon is 4.4, instead of the previously accepted twelve.
Despite his serious mistakes, it was Dalton who was the first to create a table of some elements. It underwent repeated changes during the scientist’s lifetime.
The isotopic component of a substance affects the relative atomic weight accuracy value
When considering the atomic masses of elements, you will notice that the accuracy for each element is different. For example, for lithium it is four-digit, and for fluorine it is eight-digit.
The problem is that the isotopic component of each element is different and not constant. For example, ordinary water contains three types of hydrogen isotopes. These include, in addition to ordinary hydrogen, deuterium and tritium.
The relative atomic mass of hydrogen isotopes is two and three, respectively. “Heavy” water (formed by deuterium and tritium) evaporates less easily. Therefore, there are fewer isotopes of water in the vapor state than in the liquid state.
Selectivity of living organisms to different isotopes
Living organisms have a selective property towards carbon. To build organic molecules, carbon with a relative atomic mass of twelve is used. Therefore, substances of organic origin, as well as a number of minerals such as coal and oil, contain less isotopic content than inorganic materials.
Microorganisms that process and accumulate sulfur leave behind the sulfur isotope 32. In areas where bacteria do not process, the proportion of sulfur isotope is 34, that is, much higher. It is on the basis of the ratio of sulfur in soil rocks that geologists come to a conclusion about the nature of the origin of the layer - whether it has a magmatic or sedimentary nature.
Of all the chemical elements, only one has no isotopes - fluorine. Therefore, its relative atomic mass is more accurate than other elements.
Existence of unstable substances in nature
For some elements, the relative mass is indicated in square brackets. As you can see, these are the elements located after uranium. The fact is that they do not have stable isotopes and decay with the release of radioactive radiation. Therefore, the most stable isotope is indicated in parentheses.
Over time, it became clear that it was possible to obtain a stable isotope from some of them under artificial conditions. It was necessary to change the atomic masses of some transuranium elements in the periodic table.
In the process of synthesizing new isotopes and measuring their lifespan, it was sometimes possible to discover nuclides with half-lives millions of times longer.
Science does not stand still; new elements, laws, and relationships between various processes in chemistry and nature are constantly being discovered. Therefore, what form chemistry and Mendeleev’s periodic system of chemical elements will appear in in the future, a hundred years from now, is vague and uncertain. But I would like to believe that the works of chemists accumulated over the past centuries will serve new, more advanced knowledge of our descendants.
