In The Skeptic Chemist (1661). Boyle pointed out that neither the four elements of Aristotle nor the three principles of the alchemists could be recognized as elements. Elements, according to Boyle, are practically indecomposable bodies (substances), consisting of similar homogeneous (consisting of primary matter) corpuscles, from which all complex bodies are composed and into which they can be decomposed. Corpuscles can vary in shape, size, weight. The corpuscles from which the bodies are formed remain unchanged during the transformations of the latter.
However, Mendeleev was forced to make several permutations in the sequence of elements, distributed by increasing atomic weight, in order to maintain the periodicity of chemical properties, and also to introduce empty cells corresponding to undiscovered elements. Later (in the first decades of the 20th century) it became clear that the periodicity of chemical properties depends on the atomic number (charge of the atomic nucleus), and not on the atomic mass of the element. The latter is determined by the number of stable isotopes of the element and their natural abundance. However, the stable isotopes of an element have atomic masses grouping around a certain value, since isotopes with an excess or deficiency of neutrons in the nucleus are unstable, and with an increase in the number of protons (that is, the atomic number), the number of neutrons that together form a stable nucleus also increases. Therefore, the periodic law can also be formulated as a dependence of chemical properties on atomic mass, although this dependence is violated in several cases.
The modern understanding of a chemical element as a collection of atoms characterized by the same positive nuclear charge, equal to the element number in the Periodic Table, appeared due to the fundamental work of Henry Moseley (1915) and James Chadwick (1920).
Known chemical elements[ | ]
The synthesis of new (not found in nature) elements with an atomic number higher than that of uranium (transuranium elements) was initially carried out using multiple neutron capture by uranium nuclei under conditions of an intense neutron flux in nuclear reactors and even more intense - under conditions of a nuclear (thermonuclear) ) explosion. The subsequent chain of beta decays of neutron-rich nuclei leads to an increase in the atomic number and the appearance of daughter nuclei with the atomic number Z> 92 . Thus neptunium was discovered ( Z= 93), plutonium (94), americium (95), berkelium (97), einsteinium (99) and fermium (100). Curium (96) and californium (98) can also be synthesized (and practically obtained) in this way, but they were originally discovered by irradiating plutonium and curium with alpha particles in an accelerator. Heavier elements, beginning with mendelevium (101), are obtained only at accelerators, by irradiating actinide targets with light ions.
The right to propose a name for a new chemical element is granted to the discoverers. However, this name must satisfy certain rules. The report of a new discovery is checked over several years by independent laboratories, and, if confirmed, the International Union of Pure and Applied Chemistry (IUPAC; Eng. International Union for Pure and Applied Chemistry, IUPAC) officially approves the name of the new element.
All 118 elements known as of December 2016 have permanent names approved by IUPAC. From the moment of the discovery application to the approval of the IUPAC name, the element appears under a temporary systematic name, derived from Latin numerals that form digits in the atomic number of the element, and is indicated by a three-letter temporary symbol formed from the first letters of these numerals. For example, the 118th element, oganesson, before the official approval of the permanent name, had the temporary name of ununoctium and the symbol Uuo.
Undiscovered or unapproved elements are often named using the system used by Mendeleev - by the name of the higher homologue in the periodic table, with the addition of the prefixes "eka-" or (rarely) "dvi-", meaning the Sanskrit numerals "one" and "two" ( depending on whether the homologue is 1 or 2 periods higher). For example, before the discovery, germanium (standing in the periodic table under silicon and predicted by Mendeleev) was called eka-silicon, oganesson (ununoctium, 118) is also called eka-radon, and flerovium (ununquadium, 114) - eka-lead.
Classification [ | ]
Symbols of chemical elements[ | ]
Symbols for chemical elements are used as abbreviations for the names of elements. As a symbol, one usually takes the initial letter of the name of the element and, if necessary, adds the next or one of the following. Usually these are the initial letters of the Latin names of the elements: Cu - copper ( cuprum), Ag - silver ( argentum), Fe - iron ( ferrum), Au - gold ( aurum), Hg - ( hydrargirum). Such a system of chemical symbols was proposed in 1814 by the Swedish chemist J. Berzelius. The temporary symbols of the elements, used before the official approval of their permanent names and symbols, consist of three letters, meaning the Latin names of the three digits in the decimal notation of their atomic number (for example, ununoctium - the 118th element - had the temporary designation Uuo). The notation system for higher homologues described above (Eka-Rn, Eka-Pb, etc.) is also used.
Smaller numbers near the symbol of the element are indicated: top left - atomic mass, bottom left - serial number, top right - ion charge, bottom right - number of atoms in a molecule:
All elements following after plutonium Pu (serial number 94) in the periodic system of D. I. Mendeleev are completely absent in the earth's crust, although some of them can be formed in space during supernova explosions [ ] . The half - lives of all known isotopes of these elements are small compared to the lifetime of the Earth . Long-term searches for hypothetical natural superheavy elements have not yet yielded results.
Most of the chemical elements, except for a few of the lightest ones, arose in the Universe mainly during stellar nucleosynthesis (elements up to iron - as a result of thermonuclear fusion, heavier elements - during successive capture of neutrons by atomic nuclei and subsequent beta decay, as well as in a number of other nuclear reactions). The lightest elements (hydrogen and helium - almost completely, lithium, beryllium and boron - partially) were formed in the first three minutes after the Big Bang (primary nucleosynthesis).
One of the main sources of especially heavy elements in the Universe should be, according to calculations, neutron star mergers, with the release of significant amounts of these elements, which subsequently participate in the formation of new stars and their planets.
Chemical elements as an integral part of chemicals[ | ]
Chemical elements form about 500 simple substances. The ability of one element to exist in the form of various simple substances that differ in properties is called allotropy. In most cases, the names of simple substances coincide with the name of the corresponding elements (for example, zinc, aluminum, chlorine), however, in the case of the existence of several allotropic modifications, the names of a simple substance and element may differ, for example, oxygen (dioxygen, O 2) and ozone (O 3) ; diamond, graphite, and a number of other allotropic modifications of carbon exist alongside amorphous forms of carbon.
Under normal conditions, 11 elements exist in the form of gaseous simple substances ( , , , , , , , , , , ), 2 - liquids ( and ), the remaining elements form solids.
see also [ | ]
Chemical elements:
Links [ | ]
- Kedrov B. M. The evolution of the concept of an element in chemistry. Moscow, 1956
- Chemistry and Life (Salter Chemistry). Part 1. The concepts of chemistry. M .: Publishing house of the RCTU im. D. I. Mendeleev, 1997
- Azimov A. Brief history of chemistry. St. Petersburg, Amphora, 2002
- Bednyakov V. A. "On the origin of chemical elements" E. Ch. A. Ya., Volume 33 (2002), Part 4 pp. 914-963.
Notes [ | ]
- The team of authors. The meaning of the word "Chemical elements" in the Great Soviet Encyclopedia (indefinite) . Soviet Encyclopedia. Archived from the original on May 16, 2014.
- Atoms and chemical elements.
- Classes of inorganic substances.
- , With. 266-267.
- Discovery and Assignment of Elements with Atomic Numbers 113, 115, 117 and 118 (indefinite) .
- Around the world - Chemical elements
- Basic Concepts of Chemistry.
- Marinov, A.; Rodushkin, I.; Kolb, D.; Pape, A.; Kashiv, Y.; Brandt, R.; Gentry, R.V.; Miller, H.W. Evidence for a long-lived superheavy nucleus with atomic mass number A=292 and atomic number Z=~122 in natural Th (English) // ArXiv.org: journal. - 2008.
- Superheavy elements found in cosmic rays // Lenta.ru. - 2011.
- With the exception of traces of primordial plutonium-244, which has a half-life of 80 million years; see Plutonium#Natural plutonium.
- Hoffman, D.C.; Lawrence, F. O.; Mewherter, J. L.; Rourke, F.M. Detection of Plutonium-244 in Nature // Nature: Article. - 1971. - Iss. 234 . - P. 132-134. - DOI:10.1038/234132a0.
- Rita Cornelis, Joe Caruso, Helen Crews, Klaus Heumann. Handbook of elemental speciation II: species in the environment, food, medicine & occupational health. - John Wiley and Sons, 2005. - 768 p. - ISBN 0470855983, 9780470855980.
- Hubble discovered the first kilonova Archived August 8, 2013. // compulenta.computerra.ru
- January 30, 2009 at the Wayback Machine (unavailable link from 21-05-2013 - , ).
Literature [ | ]
- Mendeleev D. I. ,.// Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - St. Petersburg. , 1890-1907.
- Chernobelskaya G.M. Methods of teaching chemistry in high school. - M.: Humanitarian publishing center VLADOS, 2000. - 336 p. - ISBN 5-691-00492-1.
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In chemical reactions, one substance is transformed into another. To understand how this happens, you need to remember from the course of natural history and physics that substances are made up of atoms. There are a limited number of types of atoms. Atoms can be connected to each other in various ways. Just as hundreds of thousands of different words are formed when the letters of the alphabet are added together, so molecules or crystals of different substances are formed from the same atoms.
Atoms can form molecules- the smallest particles of a substance that retain its properties. For example, several substances are known that are formed from only two types of atoms - oxygen atoms and hydrogen atoms, but by different types of molecules. These substances include water, hydrogen and oxygen. The water molecule consists of three particles connected to each other. This is what atoms are.
To the oxygen atom (oxygen atoms are denoted in chemistry by the letter O) two hydrogen atoms are attached (they are denoted by the letter H).
An oxygen molecule is made up of two oxygen atoms; A hydrogen molecule is made up of two hydrogen atoms. Molecules can be formed in the course of chemical transformations, or they can decay. Thus, each water molecule breaks down into two hydrogen atoms and one oxygen atom. Two water molecules form twice as many hydrogen and oxygen atoms.
Identical atoms bond in pairs to form molecules of new substances- hydrogen and oxygen. Molecules are thus destroyed, while atoms are preserved. This is where the word "atom" came from, which means in translation from ancient Greek "indivisible".
Atoms are the smallest chemically indivisible particles of matter.
In chemical transformations, other substances are formed from the same atoms that made up the original substances. Just as microbes became available for observation with the invention of the microscope, so atoms and molecules became accessible with the invention of devices that give even greater magnification and even allow atoms and molecules to be photographed. In such photographs, atoms look like blurry spots, and molecules look like a combination of such spots. However, there are also phenomena in which atoms divide, atoms of one type turn into atoms of other types. At the same time, artificially obtained and such atoms that are not found in nature. But these phenomena are studied not by chemistry, but by another science - nuclear physics. As already mentioned, there are other substances, which include hydrogen and oxygen atoms. But, regardless of whether these atoms are included in the composition of water molecules, or in the composition of other substances, these are atoms of the same chemical element.
A chemical element is a specific type of atom How many types of atoms are there? To date, a person is reliably aware of the existence of 118 types of atoms, that is, 118 chemical elements. Of these, 90 types of atoms are found in nature, the rest are obtained artificially in laboratories.
Symbols of chemical elements
In chemistry, chemical symbols are used to designate chemical elements. It's the language of chemistry. To understand speech in any language, you need to know the letters, in chemistry in the same way. In order to understand and describe the properties of substances, and the changes that occur with them, it is first of all necessary to know the symbols of chemical elements. In the era of alchemy, the chemical elements were known much less than now. Alchemists identified them with planets, various animals, ancient deities. Currently, the notation introduced by the Swedish chemist Jöns Jakob Berzelius is used all over the world. In his system, chemical elements are denoted by the initial or one of the subsequent letters of the Latin name of a given element. For example, the element silver is denoted by the symbol - Ag (lat. Argentum). Below are the symbols, pronunciations of the symbols, and the names of the most common chemical elements. They need to be memorized!
The Russian chemist Dmitri Ivanovich Mendeleev was the first to order the variety of chemical elements, and on the basis of the Periodic Law he discovered, he compiled the Periodic Table of chemical elements. How is the Periodic Table of chemical elements arranged? Figure 58 shows a short period version of the Periodic System. The Periodic System consists of vertical columns and horizontal rows. The horizontal lines are called periods. To date, all known elements are placed in seven periods.
Periods are designated by Arabic numerals from 1 to 7. Periods 1-3 consist of one row of elements - they are called small.
Periods 4–7 consist of two rows of elements, they are called large. The vertical columns of the Periodic System are called groups of elements.
There are eight groups in total, and Roman numerals from I to VIII are used to designate them.
Allocate main and secondary subgroups. Periodic System- a universal reference book of a chemist, with its help you can get information about chemical elements. There is another type of Periodic System - long period. In the long period form of the Periodic Table, the elements are grouped differently, and are divided into 18 groups.
PeriodicSystems elements are grouped by "families", that is, in each group of elements there are elements with similar, similar properties. In this variant Periodic System, group numbers, as well as periods, are denoted by Arabic numerals. Periodic System of Chemical Elements D.I. Mendeleev
The prevalence of chemical elements in nature
Atoms of elements found in nature, distributed in it very unevenly. In space, the most common element is hydrogen, the first element in the Periodic Table. It accounts for about 93% of all atoms in the universe. About 6.9% are helium atoms - the second element of the Periodic Table.
The remaining 0.1% is accounted for by all other elements.
The abundance of chemical elements in the earth's crust differs significantly from their abundance in the universe. The earth's crust contains the most oxygen and silicon atoms. Together with aluminum and iron, they form the main compounds of the earth's crust. And iron and nickel- the main elements that make up the core of our planet.
Living organisms also consist of atoms of various chemical elements. The human body contains the most carbon, hydrogen, oxygen and nitrogen atoms.
The result of the article about Chemical elements.
- Chemical element- a certain type of atom
- To date, a person is reliably aware of the existence of 118 types of atoms, that is, 118 chemical elements. Of these, 90 types of atoms are found in nature, the rest are artificially obtained in laboratories.
- There are two versions of the Periodic Table of Chemical Elements by D.I. Mendeleev - short term and long term
- Modern chemical symbolism is formed from the Latin names of chemical elements
- Periods- horizontal lines of the Periodic System. Periods are divided into small and large
- Groups- vertical rows of the periodic table. Groups are divided into main and secondary
A chemical element is a collective term that describes a set of atoms of a simple substance, that is, one that cannot be divided into any simpler (according to the structure of their molecules) components. Imagine that you receive a piece of pure iron with a request to split it into hypothetical constituents using any device or method ever invented by chemists. However, you can't do anything, the iron will never be divided into something simpler. A simple substance - iron - corresponds to the chemical element Fe.
Theoretical definition
The experimental fact noted above can be explained using the following definition: a chemical element is an abstract collection of atoms (not molecules!) of the corresponding simple substance, i.e., atoms of the same type. If there were a way to look at each of the individual atoms in the piece of pure iron mentioned above, then they would all be the same - iron atoms. In contrast, a chemical compound, such as iron oxide, always contains at least two different kinds of atoms: iron atoms and oxygen atoms.
Terms you should know
Atomic mass: the mass of protons, neutrons and electrons that make up an atom of a chemical element.
atomic number: the number of protons in the nucleus of an element's atom.
chemical symbol: a letter or pair of Latin letters representing the designation of the given element.
Chemical compound: a substance that consists of two or more chemical elements combined with each other in a certain proportion.
Metal: An element that loses electrons in chemical reactions with other elements.
Metalloid: An element that reacts sometimes as a metal and sometimes as a non-metal.
Non-metal: an element that seeks to obtain electrons in chemical reactions with other elements.
Periodic system of chemical elements: a system for classifying chemical elements according to their atomic numbers.
synthetic element: one that is obtained artificially in the laboratory, and usually does not occur in nature.
Natural and synthetic elements
Ninety-two chemical elements occur naturally on Earth. The rest were obtained artificially in laboratories. A synthetic chemical element is typically the product of nuclear reactions in particle accelerators (devices used to increase the speed of subatomic particles such as electrons and protons) or nuclear reactors (devices used to manipulate the energy released from nuclear reactions). The first synthetic element obtained with atomic number 43 was technetium, discovered in 1937 by Italian physicists C. Perrier and E. Segre. Apart from technetium and promethium, all synthetic elements have nuclei larger than those of uranium. The last synthetic element to be named is livermorium (116), and before that was flerovium (114).
Two dozen common and important elements
| Name | Symbol | Percentage of all atoms * | Properties of chemical elements (under normal room conditions) |
|||
| In the Universe | In the earth's crust | In sea water | In the human body |
|||
| Aluminum | Al | - | 6,3 | - | - | Lightweight, silver metal |
| Calcium | Ca | - | 2,1 | - | 0,02 | Included in natural minerals, shells, bones |
| Carbon | FROM | - | - | - | 10,7 | Basis of all living organisms |
| Chlorine | Cl | - | - | 0,3 | - | poisonous gas |
| Copper | Cu | - | - | - | - | Only red metal |
| Gold | Au | - | - | - | - | Only yellow metal |
| Helium | He | 7,1 | - | - | - | Very light gas |
| Hydrogen | H | 92,8 | 2,9 | 66,2 | 60,6 | The lightest of all elements; gas |
| Iodine | I | - | - | - | - | Non-metal; used as an antiseptic |
| Iron | Fe | - | 2,1 | - | - | Magnetic metal; used for the production of iron and steel |
| Lead | Pb | - | - | - | - | Soft, heavy metal |
| Magnesium | mg | - | 2,0 | - | - | Very light metal |
| Mercury | hg | - | - | - | - | Liquid metal; one of two liquid elements |
| Nickel | Ni | - | - | - | - | Corrosion resistant metal; used in coins |
| Nitrogen | N | - | - | - | 2,4 | Gas, the main component of air |
| Oxygen | O | - | 60,1 | 33,1 | 25,7 | Gas, the second important air component |
| Phosphorus | R | - | - | - | 0,1 | Non-metal; important for plants |
| Potassium | To | - | 1.1 | - | - | Metal; important for plants; commonly referred to as "potash" |
* If the value is not specified, then the element is less than 0.1 percent.
Big bang as the root cause of the formation of matter
What chemical element was the very first in the universe? Scientists believe that the answer to this question lies in the stars and the processes by which stars are formed. The universe is believed to have originated at some point in time between 12 and 15 billion years ago. Until this moment, nothing that exists, except for energy, is conceived. But something happened that turned this energy into a huge explosion (the so-called Big Bang). In the seconds following the Big Bang, matter began to form.
The first simplest forms of matter to appear were protons and electrons. Some of them are combined into hydrogen atoms. The latter consists of one proton and one electron; it is the simplest atom that can exist.
Slowly, over long periods of time, hydrogen atoms began to gather together in certain regions of space, forming dense clouds. Hydrogen in these clouds was pulled into compact formations by gravitational forces. Eventually these clouds of hydrogen became dense enough to form stars.
Stars as chemical reactors of new elements
A star is simply a mass of matter that generates the energy of nuclear reactions. The most common of these reactions is the combination of four hydrogen atoms to form one helium atom. As soon as stars began to form, helium became the second element to appear in the universe.
As stars get older, they switch from hydrogen-helium nuclear reactions to other types. In them, helium atoms form carbon atoms. Later carbon atoms form oxygen, neon, sodium and magnesium. Still later, neon and oxygen combine with each other to form magnesium. As these reactions continue, more and more chemical elements are formed.
The first systems of chemical elements
Over 200 years ago, chemists began looking for ways to classify them. In the middle of the nineteenth century, about 50 chemical elements were known. One of the questions that chemists sought to resolve. boiled down to the following: is a chemical element a substance completely different from any other element? Or are some elements related to others in some way? Is there a common law that unites them?
Chemists have proposed various systems of chemical elements. So, for example, the English chemist William Prout in 1815 suggested that the atomic masses of all elements are multiples of the mass of the hydrogen atom, if we take it equal to one, that is, they must be integers. At that time, the atomic masses of many elements had already been calculated by J. Dalton in relation to the mass of hydrogen. However, if this is approximately the case for carbon, nitrogen, oxygen, then chlorine with a mass of 35.5 did not fit into this scheme.
The German chemist Johann Wolfgang Döbereiner (1780-1849) showed in 1829 that three elements from the so-called halogen group (chlorine, bromine and iodine) could be classified according to their relative atomic masses. The atomic weight of bromine (79.9) turned out to be almost exactly the average of the atomic weights of chlorine (35.5) and iodine (127), namely 35.5 + 127 ÷ 2 = 81.25 (close to 79.9). This was the first approach to the construction of one of the groups of chemical elements. Doberiner discovered two more such triads of elements, but he failed to formulate a general periodic law.
How did the periodic table of chemical elements appear?
Most of the early classification schemes were not very successful. Then, around 1869, almost the same discovery was made by two chemists at almost the same time. The Russian chemist Dmitri Mendeleev (1834-1907) and the German chemist Julius Lothar Meyer (1830-1895) proposed organizing elements that have similar physical and chemical properties into an ordered system of groups, series, and periods. At the same time, Mendeleev and Meyer pointed out that the properties of chemical elements are periodically repeated depending on their atomic weights.
Today, Mendeleev is generally considered to be the discoverer of the periodic law because he took one step that Meyer did not. When all the elements were located in the periodic table, some gaps appeared in it. Mendeleev predicted that these were sites for elements that had not yet been discovered.
However, he went even further. Mendeleev predicted the properties of these not yet discovered elements. He knew where they were located on the periodic table, so he could predict their properties. Remarkably, every chemical element Mendeleev predicted, the future gallium, scandium, and germanium, were discovered less than ten years after he published his periodic law.
Short form of the periodic table
There were attempts to calculate how many variants of the graphic representation of the periodic system were proposed by different scientists. It turned out to be more than 500. Moreover, 80% of the total number of options are tables, and the rest are geometric shapes, mathematical curves, etc. As a result, four types of tables have found practical application: short, semi-long, long and ladder (pyramidal). The latter was proposed by the great physicist N. Bohr.
The figure below shows the short form.
In it, the chemical elements are arranged in ascending order of their atomic numbers from left to right and from top to bottom. So, the first chemical element of the periodic table, hydrogen, has atomic number 1 because the nuclei of hydrogen atoms contain one and only one proton. Similarly, oxygen has an atomic number of 8, since the nuclei of all oxygen atoms contain 8 protons (see the figure below).
The main structural fragments of the periodic system are periods and groups of elements. In six periods, all cells are filled, the seventh is not yet completed (elements 113, 115, 117 and 118, although synthesized in laboratories, have not yet been officially registered and do not have names).
Groups are divided into main (A) and secondary (B) subgroups. The elements of the first three periods, containing one series-line each, are included exclusively in A-subgroups. The remaining four periods include two rows each.
Chemical elements in the same group tend to have similar chemical properties. So, the first group consists of alkali metals, the second - alkaline earth. Elements in the same period have properties that slowly change from an alkali metal to a noble gas. The figure below shows how one of the properties - atomic radius - changes for individual elements in the table.
Long period form of the periodic table
It is shown in the figure below and is divided in two directions, by rows and by columns. There are seven period rows, as in the short form, and 18 columns, called groups or families. In fact, the increase in the number of groups from 8 in short form to 18 in long form is obtained by placing all elements in periods starting from the 4th, not in two, but in one line.
Two different numbering systems are used for groups, as shown at the top of the table. The Roman numeral system (IA, IIA, IIB, IVB, etc.) has traditionally been popular in the US. Another system (1, 2, 3, 4, etc.) is traditionally used in Europe and was recommended for use in the USA a few years ago.
The appearance of the periodic tables in the figures above is a little misleading, as with any such published table. The reason for this is that the two groups of elements shown at the bottom of the tables should actually be located within them. The lanthanides, for example, belong to period 6 between barium (56) and hafnium (72). In addition, the actinides belong to period 7 between radium (88) and rutherfordium (104). If they were pasted into a table, it would be too wide to fit on a piece of paper or a wall chart. Therefore, it is customary to place these elements at the bottom of the table.
All the diversity of nature around us consists of combinations of a relatively small number of chemical elements. So what is the characteristic of a chemical element, and how does it differ from a simple substance?
Chemical element: history of discovery
In different historical epochs, different meanings were put into the concept of “element”. Ancient Greek philosophers considered 4 “elements” as such “elements” - heat, cold, dryness and humidity. Combining in pairs, they formed four "beginnings" of everything in the world - fire, air, water and earth.
In the 17th century, R. Boyle pointed out that all elements are of a material nature and their number can be quite large.
In 1787, the French chemist A. Lavoisier created the "Table of Simple Bodies". It included all the elements known by that time. The latter were understood as simple bodies that could not be decomposed by chemical methods into even simpler ones. Subsequently, it turned out that some complex substances were included in the table.
By the time D. I. Mendeleev discovered the periodic law, only 63 chemical elements were known. The discovery of the scientist not only led to an orderly classification of chemical elements, but also helped to predict the existence of new, not yet discovered elements.
Rice. 1. A. Lavoisier.
What is a chemical element?
A certain type of atom is called a chemical element. Currently, 118 chemical elements are known. Each element is denoted by a symbol that represents one or two letters from its Latin name. For example, the element hydrogen is denoted by the Latin letter H and the formula H 2 - the first letter of the Latin name of the element Hydrogenium. All sufficiently well studied elements have symbols and names that can be found in the main and secondary subgroups of the Periodic Table, where they are all arranged in a certain order.
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There are many types of systems, but the generally accepted is the Periodic system of chemical elements of D. I. Mendeleev, which is a graphical expression of the Periodic law of D. I. Mendeleev. Usually, the short and long forms of the Periodic Table are used.
Rice. 2. Periodic system of elements of D. I. Mendeleev.
What is the main feature by which an atom is attributed to a particular element? D. I. Mendeleev and other chemists of the 19th century considered the mass as the most stable characteristic of the atom to be the main feature of the atom, therefore the elements in the Periodic Table are arranged in ascending order of atomic mass (with a few exceptions).
According to modern concepts, the main property of an atom, relating it to a particular element, is the charge of the nucleus. Thus, a chemical element is a type of atoms characterized by a certain value (value) of the part of the chemical element - the positive charge of the nucleus.
Of all the existing 118 chemical elements, most (about 90) can be found in nature. The rest are obtained artificially using nuclear reactions. Elements 104-107 were synthesized by physicists at the Joint Institute for Nuclear Research in Dubna. Currently, work continues on the artificial production of chemical elements with higher serial numbers.
All elements are divided into metals and non-metals. More than 80 elements are metals. However, this division is conditional. Under certain conditions, some metals may exhibit non-metallic properties, and some non-metals may exhibit metallic properties.
The content of various elements in natural objects varies widely. 8 chemical elements (oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium) make up 99% of the earth's crust by mass, all the rest are less than 1%. Most chemical elements are of natural origin (95), although some of them were originally artificially derived (for example, promethium).
It is necessary to distinguish between the concepts of "simple substance" and "chemical element". A simple substance is characterized by certain chemical and physical properties. In the process of chemical transformation, a simple substance loses some of its properties and enters a new substance in the form of an element. For example, nitrogen and hydrogen, which are part of ammonia, are contained in it not in the form of simple substances, but in the form of elements.
Some elements are combined into groups, such as organogens (carbon, oxygen, hydrogen, nitrogen), alkali metals (lithium, sodium, potassium, etc.), lanthanides (lanthanum, cerium, etc.), halogens (fluorine, chlorine, bromine, etc.), inert elements (helium, neon, argon)
Rice. 3. Halogens table.
What have we learned?
When introducing a 8th grade chemistry course, it is first necessary to study the concept of a “chemical element”. at present, 118 chemical elements are known, arranged in the table of D. I. Mendeleev according to the increase in atomic mass, and having basic acidic properties.
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