A chemical element is a type of atom with a certain value of the positive charge of the nucleus and a certain set of properties.
Currently, 112 chemical elements are known. Some elements have been used by man since ancient times, others were discovered in nature in the 18th - 20th centuries. About 20 elements do not exist in nature, they are obtained artificially using nuclear reactions.
All elements have names and symbols. The symbol of an element is its designation by the first letter or the first two letters of the Latin name of the chemical element.
The great Russian chemist D.I. Mendeleev established that there is a regular relationship between all chemical elements, which he called the periodic law (1869). A visual representation of this law is the well-known table - the Periodic system of chemical elements of D.I. Mendeleev. It contains symbols, names and the most important characteristics of the elements.
Note. The symbols of many chemical elements are understandable, because their Russian and Latin names are consonant, for example Ca - calcium (Calzium), Na - sodium (Natrium), etc. But for some elements, Russian and Latin names are very different, for example, Fe - iron (Ferrum), Au - gold (Aurum), Ag - silver (Argentum), O - oxygen (Oxigenium), H - hydrogen (Hidrogenium), C - carbon (Carboneum), etc. The reference book, which is recommended for use in the study of chemistry (Stas N.F. Handbook of General and Inorganic Chemistry), contains two forms of the Periodic System (8-cell and 18-cell) and a table with Russian, Latin, English, German and French names chemical elements.
If the number of chemical elements is 112, and the element is a type of atom, then there must be 112 types of atom. In reality, this is not so. It has been found that almost every chemical element is a collection of several isotopes. Isotopes are atoms that have the same nuclear charge, but a different number of neutrons in the nucleus. Isotopes are denoted by chemical element symbols with an index at the top left that indicates the mass number. The mass number of an atom (isotope) is the sum of protons and neutrons contained in the nucleus of an atom, for example: 35 Cl, 37 Cl, 29 Mg, 29 Mg, 29 Mg, etc.
The mass of the nucleus of an atom (isotope) is always somewhat less than the mass number. The decrease in mass during the formation of atomic nuclei ( mass defect) is explained by the fact that in the nuclei of atoms there are huge forces of attraction between protons and neutrons. The emergence of these forces is accompanied by a mass defect according to Einstein's theory of relativity.
The mass number of any isotope is an integer, but the atomic mass of an element is not. This is explained by the fact that the atomic mass of an element is the average value of the atomic masses of its isotopes, taking into account their abundance in nature.
Example 1 Calculate the atomic mass of ... which has .... an isotope
3. Simple substances and compounds
Simple substances are substances that contain atoms of the same chemical element.
A simple substance and a chemical element are not identical concepts, although such an identification is sometimes mistakenly made. Historically, simple substances are called the same as chemical elements, but these are not the same thing. For example, they say: 1) water (H 2 O) contains oxygen; 2) we breathe oxygen. In the first case, we are talking about the chemical element oxygen, and in the second, about the substance O 2, which is in the air.
If the concepts of "chemical element" and "simple substance" were identical concepts, then there would be as many simple substances as there are chemical elements (112), but in reality there are several hundred of them. This is explained by the fact that many elements form not one, but several simple substances. This phenomenon is called allotropy. Different simple substances formed by the same chemical element are called allotropic modifications(modifications) of this substance. They differ in the composition of molecules (O 2, O 3), crystal structure (diamond, graphite), or both (white phosphorus - P 4 molecules, red - polymeric substance).
Substances that contain atoms of various chemical elements are called complex. Compounds are called chemical compounds. They are subdivided into organic (they are studied organic chemistry) and inorganic.
Inorganic compounds are diverse in composition and properties. In chemical practice, most often one has to deal with four classes of inorganic compounds: oxides, bases, acids and salts. These classes of inorganic compounds are called the most important or basic. Each class of the most important compounds, in turn, is subdivided into groups of substances with similar properties. The next chapter of this manual is devoted to the classification, properties and nomenclature of inorganic compounds.
It takes only one sheet, but this sheet contains a huge amount of information. Each cell of the table contains the international symbol of the element, its name (in our tables - in Russian), its serial number, relative atomic mass (for unstable elements - mass number). As a rule, the belonging of elements to a particular family is highlighted in color, and the structure of the electron shells of atoms is also given. Some firms produce colorful tables, in which each cell contains a photograph of the corresponding simple substance, the structure of the most stable crystal lattice, provides information about the use of this element. The design of cells with radioactive elements is interestingly solved. So, in one table, in place of radium, there is a photograph of Marie Curie's working journal, open on the page where the entry about the discovery of a new element first appeared.
The original series of fifteen color postcards was produced by the association of French chemists. It contains photographs of postage stamps issued in many countries of the world. Each stamp is dedicated to another chemical element. And, of course, a portrait of the creator of the periodic system of elements, D.I. Mendeleev, and a photograph of the first handwritten sketch of his table, take pride of place. On the stamps there are portraits of scientists who discovered the elements, the minerals from which these elements are mined, their crystal lattices, structural formulas compounds ... And when the owner of this philatelic collection, a professor of chemistry from the University of Dijon, Jean Tiroufle, could not find a suitable stamp, he cleverly got out of the situation, resorting to allegory. So, in place of gallium is placed French stamp with a singing rooster. And this is no accident. The element gallium was predicted by Mendeleev (as eka-aluminum) and discovered in 1875 by the French chemist Paul Emile Lecoq de Boisbaudran, who named it after his homeland (Gallia is the Latin name for France). The symbol of France is a rooster (in French - le coq), so in the name of the element its discoverer implicitly perpetuated his surname as well!
Even Mendeleev said that the table of elements was the fruit not only of his own work, but also of the efforts of many chemists, among whom he especially noted the “strengtheners of the periodic law” who discovered the elements he predicted. To create a modern table, it took many years of hard work of thousands and thousands of chemists and physicists. If Mendeleev were alive now, looking at the modern table of elements, he could well repeat the words of the English chemist J. W. Mellor, the author of the classic 16-volume encyclopedia on inorganic and theoretical chemistry. Having finished in 1937, after 15 years of work, his work, he wrote with gratitude on title page: “Dedicated to the privates of a huge army of chemists. Their names are forgotten, their works remain"...
Now few people know the names of those who proposed the modern scale of atomic masses, for the first time divided the mythical element "didim" into praseodymium and neodymium, synthesized technetium and found traces of it in the earth's crust - in a word, all those who, by their work, made at least a small contribution to element table. But the table is in front of us, and the amount of information it contains is enormous. Its beginning extends deep into the centuries, in ancient times, when the Greek philosopher Leucippus and his famous student Democritus formulated the first ideas about atoms.
Latin word element ( elementum) was used by ancient authors (Cicero, Ovid, Horace), and in many respects in the same sense as its modern meaning - as part of something (an element of speech, an element of education, etc.). The origin of the name of this word is interesting. In ancient times, the saying was widespread: “As words are made up of letters, so the body is made up of elements.” Hence the probable origin of this word: by the name of a number of consonant letters in the Latin alphabet: l, m, n, t ("el" - "em" - "en" - "tum").
Close in meaning to the Romans was the word principle in meaning " component", "Start". The ancient Roman philosopher Titus Lucretius Car in his poem On the nature of things frequently used the term principle(translated as "original"). In this sense, it is very close to the modern "chemical" concept of an element:
As for the beginnings, they have even more
means for different things to arise from them,
There is none of the things available to our eyes,
So that it consists of completely homogeneous beginnings ...
The origins of things are carried away by their own weight
Or pushing others...
(About the nature of things. Titus Lucretius Car)
The doctrine that all substances are made up of tiny particles is called the atomistic theory. The guesses of the ancients, based only on reflection, are not so far, in principle, from modern ideas: there is a limited number of different types of atoms (i.e. elements) that can combine with each other in different ways, giving a huge variety of substances with different properties. And the process of restructuring the mutual arrangement of atoms is the essence of a chemical reaction. The concept of atoms, elements - greatest achievement human mind. The laureate spoke very figuratively about this Nobel Prize in physics Richard Feynman: “If, as a result of some kind of world catastrophe, all the accumulated scientific knowledge would be destroyed and only one phrase would pass to the coming generations of living beings, then what statement, composed of the least number of words, would bring most information? I believe it is - atomic hypothesis(you can call it not a hypothesis, but a fact, but this does not change anything): all bodies are made of atoms - small bodies that are in constant motion, attract at a short distance, but repel if one of them is pressed closer to the other. In this one phrase ... contains incredible amount of information about the world, you just have to put a little imagination and a little consideration into it.
Atoms of the same kind make up a chemical element. Back in the 17th century. Robert Boyle, and in the next century - M.V. Lomonosov and A.L. Lavoisier clearly formulated the concept of "element" as a simple substance that cannot be decomposed into its constituent parts by chemical methods. The modern definition of a chemical element is very concise: an element is a collection of atoms with a certain nuclear charge Z. Core charge is equal to the number protons in it; it is it that determines the essence of a chemical element, its individuality and difference from all other elements. Therefore, it should be recognized that a colorless light gas consisting of H 2 molecules and positively charged H + cations in aqueous solutions acids, and anions H - in melts of lithium hydride LiH, and protons in physical accelerators or in the depths of the Sun, and "cold" neutral atoms H in interstellar spaces - all this is the element hydrogen ( Z= 1). Moreover, heavy varieties hydrogen- deuterium (D) and tritium (T), containing, in addition to one proton, one or two neutrons, as well as artificially obtained superheavy atoms 4 H and 5 H, also belong to the element hydrogen.
In total, 90 different elements were found in nature, and more than 20 were obtained artificially. In nature, chemical elements are part of simple and complex substances. Simple substances are formed by atoms of the same chemical element, while complex substances contain atoms of two or more elements.
Very figuratively about the difference between the concepts of an element and a simple substance, the American chemist Alexander Smith, the author of one of the best textbooks inorganic chemistry of the early 20th century: “It will be correct if we talk about the element iron and the element sulfur in iron sulfide; but the chemist will never say that this compound contains simple substances: iron and sulfur. If he had said this, then we would have understood him in such a way that the given material is not a compound, but a mixture; we would expect parts of this material to be magnetic, like iron, while other parts are yellow and soluble in carbon disulfide – which is not the case.”
But even simple substances, it turns out, are not so “simple”: most elements can form several simple bodies. According to the definition given in the Chemical Encyclopedia, a simple substance is a form of existence of a chemical element that differs in the number of atoms in molecules (for example, oxygen O 2 and ozone O 3), the type of crystal lattice (for example, modifications of carbon - graphite, diamond, carbine) or other properties. So hydrogen gas at room temperature contains two simple substances - two varieties of hydrogen (orthohydrogen and parahydrogen); they differ mutual arrangement nuclear spins ( cm. MOMENTS OF ATOMS AND NUCLEI) and hydrogen can be divided into two simple substances that differ in their physical properties (for example, heat capacities). And even gases such as H 2 , D 2 , T 2 , HD, HT, DT should be considered different simple substances, since each gas contains atoms of only one element - hydrogen, and their properties vary greatly. Several simple substances form O 2 molecules: two varieties of gaseous oxygen (they are called singlet and triplet, they differ in electronic structure and reactivity), and at least four (!) varieties of solid oxygen (in general, the presence of several crystalline modifications for one element - the rule rather than the exception). And then there is ozone... It is not surprising that the number of known simple substances is many times greater than the number of known elements.
In Russian, the same terms are usually used to designate both elements and simple substances. This is not very difficult for chemists, since it is almost always clear from the context what is at stake. So, saying "copper coin", "smelting copper from ores", "high electrical conductivity of copper", always mean metallic copper - a simple substance. Speaking about the small distribution of copper in nature, they do not mean a metal at all (native copper is an exceptionally rare mineral), but an element of copper, the atoms of which can be included in various minerals. Claiming that "copper occupies a place in the periodic table between nickel and zinc", the chemist also does not mean pieces of metal in the cells of the table, but the element copper as a combination of its atoms with a nuclear charge Z = 29.
Different terms for an element and the simple substances it forms are rare. In addition to deuterium and tritium, carbon should be mentioned. Carbon is “birthing coal”, but it is not coal itself, but a chemical element. Carbon is found in ocean water and the atmosphere, in the body of humans and animals, and in many minerals. The core of the pencil and the decoration on the ring are made of simple substances - graphite and diamond. Now other simple substances formed by the element carbon are also known - lonsdaleite, carbyne, various fullerenes, nanotubes (fullerenes and nanotubes are often combined under the same name "fullerite").
The concept of a simple substance, like many other basic concepts of chemistry, is somewhat arbitrary. After all, the "iron" nail is not made of iron at all, but of low-carbon steel containing a small amount of carbon. A gold coin contains at least 10% copper or silver (pure gold is very soft). And even the purest semiconductor silicon contains negligible amounts of atoms of other elements. The number of relatively pure simple substances that surround us in everyday life is small: aluminum and copper in wires, tungsten, molybdenum, krypton in electric light bulbs, hydrogen and helium in balloons, silver, gold, platinum, palladium in high-grade jewelry and coins, mercury in thermometer, tin on a tin can, chrome and nickel on metal products, sulfur for plant pest control, zinc in electric batteries...
Atoms (or rather nuclei) of any chemical element are built from a whole number of the simplest "bricks" - the nuclei of hydrogen atoms (protons) and uncharged neutrons. The number of protons determines which particular element the given nucleus belongs to. But the number of protons in the nuclei of atoms of a given element can be different (the sum of protons and neutrons in the nucleus is called the mass number). Varieties of atoms of a given element, differing in the number of neutrons in the nucleus and, therefore, in mass, are called isotopes. This term was proposed in 1910 by the English chemist Frederick Soddy, who derived it from the Greek words isos - equal, identical and topos - place, i.e. occupying the same cell in the periodic table. Different isotopes of a given element are named in the same way as the element itself with the addition of a mass number: chlorine-35, chlorine-37. The isotopes are designated by the symbols of the corresponding element, indicating the mass number at the top left: 35 Cl, 37 Cl, etc. A specific nucleus (or atom) with a certain mass number is called a nuclide (from the Latin nucleus - nucleus). Therefore, the following statement will be correct: natural chlorine is represented by two isotopes, oxygen by three (nuclides 16 O, 17 O and 18 O), sulfur by four, titanium by five, calcium by six, molybdenum by seven, cadmium by eight, xenon by nine , and the record belongs to tin - it has ten isotopes (nuclides from 112 Sn to 124 Sn, with the exception of 113 Sn, 121 Sn and 123 Sn. Some elements in nature are represented by only one nuclide - these are 9 Be, 19 F, 23 Na, 27 Al , 31 P, 45 Sc, 59 Co, 75 As, 89 Y, 93 Nb, 103 Rh, 127 I, 133 Cs, 141 Pr, 159 Tb, 165 Ho, 169 Tm, 197 Au, 209 Bi (only stable, that is, non-radioactive nuclides.) It is noteworthy that all the so-called "single elements" are represented by nuclides with an odd mass number.
In Soddy's time, isotopes were the name given to the various radioactive varieties of atoms of a given element. At the same time, the belonging of a particular nuclide to a given element was often unknown, and many of them had their own names, for example, RaA (nuclide 218 Po), RaB (214 Pb), RaC (214 Bi), RaC "(214 Po), RaC" " (210 Tl), RaD (210 Pb), RaE (210 Bi), two "mesothorium": MsTh 1 (nuclide 228 Ra) and MsTh 2 (nuclide 228 Ac) "radiothorium" RdTh (nuclide 228 Th), gaseous isotopes of radon - "emanation" (from the Latin emanatio– outflow): emanation of radium RaEm (nuclide 222 Rn), actinium AcEm (nuclide 219 Rn) and thorium ThEm (nuclide 220 Rn), etc. Some of these names are still occasionally used in radiochemistry. Currently, different names are generally accepted only for hydrogen isotopes - protium (1 H), deuterium (2 H or D), tritium (3 H or T). This happens because hydrogen is one of the most important elements, and its different isotopes very much - several times - differ in mass and therefore have not only different physical properties but also different reactivity. For example, deuterium and its compounds are generally less reactive and react more slowly than the light isotope (kinetic isotope effect). Currently, about 280 stable and more than 2000 radioactive isotopes of chemical elements are known.
Ilya Leenson
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All the matter around us that we see is made up of various atoms. Atoms differ from each other in structure, size and mass. There are more than 100 types of different atoms, more than 20 types of atoms were obtained by man and are not found in nature, as they are unstable and decay into simpler atoms.
However, even atoms belonging to the same species can differ slightly from each other. Therefore, there is such a thing as a chemical element - these are atoms of the same type. They all have the same nuclear charge, that is, the same number of protons.
Each chemical element has a name and designation in the form of one or two letters from the Latin name of this element. For example, the chemical element hydrogen is denoted by the letter H (from the Latin name Hydrogenium), chlorine - Cl (from Chlorum), carbon - C (from Carboneum), gold - Au (from Aurum), copper - Cu (from Cuprum), oxygen - O (from Oxigeium).
The existing chemical elements are listed in the Periodic Table of Mendeleev. Often they talk about it as a system (periodic system), because there are certain strict rules by which this or that element is placed in its cell of the table. Regular changes in the properties of elements are observed in the rows and columns of the periodic table. Thus, each element in the table has its own number.
The atoms of chemical elements do not change as a result of chemical reactions. The set of substances formed by atoms changes, but not themselves. For example, if as a result of a chemical reaction carbonic acid (H 2 CO 3) decomposed into water (H 2 O) and carbon dioxide (CO 2), then no new atoms were formed. Only the connections between them have changed.
Thus, an atom can be defined as the smallest chemically indivisible particle of matter.
Hydrogen is the most abundant element in the universe, followed by helium. These are the simplest chemical elements. The remaining chemical elements account for about 0.1% of all atoms. However, the atoms of other chemical elements have a greater mass than the atoms of hydrogen and helium. Therefore, if we express the content of the remaining chemical elements in the Universe in mass percent, then they will account for 2% of the mass of the entire substance of the Universe.
On Earth, the abundance of chemical elements is very different, if we consider the entire Universe. The Earth is dominated by oxygen (O) and silicon (Si). They account for about 75% of the mass of the Earth. Next come aluminum (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), magnesium (Mg), hydrogen (H) and many other elements in descending order.
IN chemical reactions transformations of one substance 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. How hundreds of thousands are formed when you add the letters of the alphabet different words, 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 different types 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 more atoms hydrogen and oxygen. 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 accessible to 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 System of chemical elements. How is the Periodic Table of chemical elements arranged? Figure 58 shows the short-term variant 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 – universal reference 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. In this variant Periodic System 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 Characteristics of an element in the Periodic TableThe 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 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.We draw conclusions from 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
