What are chemical elements? System and characteristics of chemical elements

A lot of different things and objects, the living and non-living bodies of nature surround us. And they all have their own composition, structure, properties. In living beings there are complex biochemical reactions that accompany life processes. Non-living bodies perform various functions in nature and life of biomass and have a complex molecular and atomic composition.

But all together the objects of the planet have a common feature: they consist of a set of tiny structural particles called atoms of chemical elements. So small that they can not be considered with the naked eye. What are chemical elements? What characteristics do they have and how did they become aware of their existence? Let's try to understand.

The concept of chemical elements

In the conventional sense, chemical elements are just a graphic representation of atoms. Particles, from which everything that exists in the universe is composed. That is, the answer to the question "what are chemical elements"? These are complex small structures, the aggregates of all isotopes of atoms, united by a common name, having their own graphic designation (symbol).

To date, we know of 118 elements that are open both in natural conditions and synthetically, by carrying out nuclear reactions and radioactive decays of the nuclei of other atoms. Each of them has a set of characteristics, its location in the common system, the history of discovery and name, and also performs a certain role in the nature and life of living beings. The study of these features is the science of chemistry. Chemical elements are the basis for constructing molecules, simple and complex compounds, and therefore chemical interactions.

History of the discovery

The very understanding of what chemical elements are, came only in the XVII century thanks to the work of Boyle. It was he who first talked about this concept and gave him the following definition. These are indivisible little simple substances, of which everything is composed, including all complex ones.

Prior to this work, the views of alchemists dominated, recognizing the theory of the four elements - Empidocles and Aristotle, and also discovered "combustible principles" (sulfur) and "metallic principles" (mercury).

Almost the entire XVIII century, the completely erroneous theory of phlogiston was spread. However, already at the end of this period, Antoine Laurent Lavoisier argues that it is untenable. He repeats Boyle's formulation, but at the same time supplements it with the first attempt to systematize all the elements known at that time, distributing them into four groups: metals, radicals, earth, non-metals.

The next big step in understanding what chemical elements are, Dalton does. He deserves credit for the discovery of the atomic mass. Based on this, it distributes some of the known chemical elements in order of increasing their atomic mass.

Stably intensive development of science and technology makes it possible to make a number of discoveries of new elements in the composition of natural bodies. Therefore, by 1869 - the time of the great creation of DI Mendeleyev - science became aware of the existence of 63 elements. The work of the Russian scientist became the first complete and permanently fixed classification of these particles.

At that time, the structure of the chemical elements was not established. It was believed that the atom is indivisible, that this is the smallest unit. With the discovery of the phenomenon of radioactivity, it was proved that it is divided into structural parts. Almost everyone in this case exists in the form of several natural isotopes (similar particles, but with a different number of neutron structures, from which the atomic mass varies). Thus, by the middle of the last century, it was possible to achieve order in the definition of the concept of a chemical element.

Mendeleyev's system of chemical elements

In the basis of the scientist put a difference in the atomic mass and managed to genius in the arrangement of all known chemical elements in the order of its increase. However, the depth and genius of his scientific thinking and foresight was that Mendeleev left empty places in his system, open cells for still unknown elements, which, in the scientist's opinion, will be discovered in the future.

And everything turned out exactly as he said. The chemical elements of Mendeleyev over time filled all the empty cells. Every structure predicted by scientists was discovered. And now we can safely say that the system of chemical elements is represented by 118 units. True, the last three discoveries have not yet been formally confirmed.

By itself, the system of chemical elements is displayed graphically by a table in which the elements are arranged according to the hierarchy of their properties, the nuclear charges and the structural features of the electron shells of their atoms. So, there are periods (7 pieces) - horizontal rows, groups (8 pieces) - vertical, subgroups (main and side within each group). Most often, two rows of families are produced separately into the lower layers of the table: lanthanides and actinides.

Periodic Mendeleev's system contains all the necessary information about chemical elements (serial number, mass number, name, sometimes the last layers of the electronic structure).

Names of elements

The right to give a name is given to the person who made the discovery of this chemical element. Many are named after the planets (uranium, plutonium, neptunium). Others were given the name in honor of the great scientists (Mendeleev, Rifford, Copernicus and others).

Often the elements are named after cities and countries (ruthenium, germanium, dubny, france, europium and others). Promise even serve mythical heroes (promethium). A phenomenon is also common where a given name is given on the properties exhibited by simple and complex substances of a given element (hydrogen, oxygen, carbon).

The names are written in Latin, but in our country there is also a Russian translation of them with fixed pronunciations. The symbol of each element is the first letter of the Latin word or the first and any of the following. Example: calcium (Ca) - Calcium, boron (B) - Boron.

Characteristics of atoms of chemical elements

Each representative of the periodic system has its own peculiarities both in structure and in manifested properties. The characteristic of a chemical element consists of analyzing the composition of its core and electronic layers, as well as the definition of the simple substance that it forms, and complex compounds.

The composition of the nucleus of atoms of chemical elements includes several particles - nucleons:

• Protons that determine its positive charge (p ⁺¹ ), as well as part of the atomic mass;
• Neutrons that affect the mass number of the element and do not have a charge (n ⁰ ).

Another kind of particle is electrons. They move around the nucleus and have a negative charge (e ^-1 ). Their orientation is not chaotic, but strictly ordered. They are located on orbitals (s, p, d and f), which form sublevels and levels (electronic layers).

The atomic mass of an element consists of protons and neutrons, the aggregate of which is called the "mass number". The number of protons is very simple - it is equal to the ordinal number of the element in the system. And since the atom as a whole is electrically neutral, that is, without any charge at all, the number of negative electrons is always equal to the number of positive proton particles.

Thus, the characteristic of a chemical element can be given by its position in a periodic system. After all, the cell describes almost everything: the serial number, and therefore, electrons and protons, the atomic mass (the average value of all existing isotopes of this element). It is evident in what period the structure is located (hence, on so many layers will be located electrons). It is also possible to predict the number of negative particles at the last energy level for the elements of the main subgroups - it is equal to the number of the group in which the element is located.

The number of neutrons can be calculated by subtracting the proton from the mass number, that is, the serial number. Thus, it is possible to obtain and compile an entire electronic-graphic formula for each chemical element, which will accurately reflect its structure and show possible oxidation states and manifested properties.

Distribution of elements in nature

The study of this issue is engaged in a whole science - cosmochemistry. The data show that the distribution of elements on our planet repeats the same patterns in the universe. The main source of light, heavy and medium atom nuclei are nuclear reactions occurring in the interior of stars - nucleosynthesis. Thanks to these processes, the Universe and outer space provided our planet with all available chemical elements.

In total, of the known 118 representatives in natural natural sources, 89 were discovered by humans. These are the most basic, most widespread atoms. Chemical elements were also synthesized artificially, by bombarding nuclei with neutrons (nucleosynthesis in laboratory conditions).

The simplest substances of such elements as nitrogen, oxygen, and hydrogen are considered to be the most numerous. Carbon is a part of all organic substances, and therefore also takes a leading position.

Classification of the electronic structure of atoms

One of the most common classifications of all chemical elements of the system is the distribution of them on the basis of electronic structure. By the number of energy levels included in the atomic shell and which contains the last valence electrons, four groups of elements can be distinguished.

S-Elements

These are those in which the s-orbital is filled with the latter. This family includes elements of the first group of the main subgroup (or alkali metals). Only one electron at the external level determines the similar properties of these representatives as strong reducing agents.

P-elements

Only 30 pieces. Valence electrons are located on the p-sublevel. These are the elements forming the main subgroups from the third to the eighth group, referring to 3,4,5,6 periods. Among them, the properties are found both in metals and in typical non-metallic elements.

D-elements and f-elements

These are transition metals from 4 to 7 a long period. Only 32 items. Simple substances can exhibit both acidic and basic properties (oxidative and reducing). Also amphoteric, that is, ambiguous.

The f-family includes lanthanoids and actinides, in which the last electrons are located on the f-orbitals.

Substances formed by elements: simple

Also, all classes of chemical elements can exist in the form of simple or complex compounds. So, it is common to consider those that are formed from the same structure in different numbers. For example, O ₂ is oxygen or dioxygen, and O ₃ is ozone. This phenomenon is called allotropy.

Simple chemical elements, forming the same name compounds, are typical for each representative of the periodic system. But not all of them are the same in terms of properties. So, there are simple substances, metals and nonmetals. The first form the main subgroups with group 1-3 and all the subgroups in the table. Non-metals form the main subgroups of 4-7 groups. The eighth basic includes special elements - noble or inert gases.

Among all the simple elements discovered so far, 11 gases, 2 liquid substances (bromine and mercury) are known under ordinary conditions, all the others are solid.

Complex connections

To those it is customary to refer all that consist of two or more chemical elements. Examples of mass, because chemical compounds are known more than 2 million! These are salts, oxides, bases and acids, complex complex compounds, all organic substances.