A lot of different things and objects, living and non-living bodies of nature surround us. And they all have their own composition, structure, properties. The living creatures undergo complex biochemical reactions that accompany life processes. Inanimate bodies perform various functions in the 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 many tiny structural particles called atoms of chemical elements. So small that the naked eye does not consider them. What are chemical elements? What characteristics do they possess and how did they become aware of their existence? Let's try to figure it out.
The concept of chemical elements
In the conventional sense, chemical elements are just a graphic representation of atoms. The particles that make up everything in the universe. That is, the question "what are chemical elements" can give such an answer. These are complex small structures, the totality of all isotopes of atoms, united by a common name, having their own graphic designation (symbol).
To date, 118 elements are known that are discovered both in vivo and synthetically through nuclear reactions and radioactive decays of the nuclei of other atoms. Each of them has a set of characteristics, its location in the general system, the history of discovery and name, and also plays a 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 the construction of molecules, simple and complex compounds, and therefore chemical interactions.
Discovery story
The very understanding of what chemical elements came only in the 17th century thanks to the work of Boyle. It was he who first spoke about this concept and gave him the following definition. These are indivisible small simple substances that make up everything around, including all complex ones.
Prior to this work, the views of the alchemists dominated, recognizing the theory of the four elements - Empidocles and Aristotle, as well as discovering the "combustible principles" (sulfur) and the "metal principles" (mercury).
Almost the entire 18th century, the completely erroneous theory of phlogiston was spread. However, 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 his first attempt to systematize all the elements known at that time, distributing them into four groups: metals, radicals, earths, non-metals.
The next big step in understanding what chemical elements are is Dalton. He owes the merit of discovering atomic mass. Based on this, it distributes part of the known chemical elements in order of increasing atomic mass.
Stably intensive development of science and technology allows us 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 D. I. Mendeleev - science became aware of the existence of 63 elements. The work of the Russian scientist became the first complete and forever entrenched classification of these particles.
The structure of chemical elements at that time was not established. It was believed that the atom is indivisible, that it is the smallest unit. With the discovery of the phenomenon of radioactivity, it was proved that it is divided into structural parts. Almost everyone at the same time exists in the form of several natural isotopes (similar particles, but with a different number of neutron structures, from which the atomic mass changes). Thus, by the middle of the last century, it was possible to achieve order in the definition of the concept of a chemical element.
Mendeleev’s chemical elements system
The scientist based the difference in atomic mass and was able to ingeniously arrange all known chemical elements in ascending order. However, the whole depth and genius of his scientific thinking and foresight consisted in the fact that Mendeleev left empty places in his system, open cells for still unknown elements that, according to the scientist, will be open in the future.
And everything turned out exactly as he said. Mendeleev’s chemical elements filled all empty cells over time. 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 officially confirmed.
The system of chemical elements itself is displayed graphically in a table in which the elements are arranged according to the hierarchy of their properties, nuclear charges and structural features of the electron shells of their atoms. So, there are periods (7 pieces) - horizontal rows, groups (8 pieces) - vertical, subgroups (main and secondary within each group). Most often, two rows of families — lanthanides and actinides — are carried separately to the lower layers of the table.
Mendeleev’s periodic system contains all the necessary information about chemical elements (serial number, mass number, name, sometimes the last layers of the electronic structure).
Item Names
The right to give a name is granted 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 (Mendelian, Rutherfordium, Copernicia, and others).
Often, elements are named after cities and countries (ruthenium, germanium, dubnium, France, europium and others). Even mythical heroes (prometheus) serve as a promise. The phenomenon is also common when a particular name is given according to the properties manifested 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 one of the following. Example: calcium (Ca) - Calcium, boron (B) - Boron.
Characterization of atoms of chemical elements
Each representative of the periodic system has its own characteristics both in the structure and in the properties shown. The characteristic of a chemical element is composed of an analysis of the composition of its nucleus and electronic layers, as well as of the definition of a simple substance formed by it and complex compounds.
The composition of the nucleus of atoms of chemical elements includes several particles - nucleons:
- protons, determining its positive charge (p +1 ), as well as part of the atomic mass;
- neutrons affecting the mass number of an element and not having a charge (n 0 ).
Another type 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 in orbitals (s, p, d and f), which form sublevels and levels (electronic layers).
The atomic mass of an element is composed of protons and neutrons, the combination of which is called the "mass number". The number of protons is determined very simply - it is equal to the ordinal number of the element in the system. And since the atom as a whole is an electrically neutral system, that is, having no 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 the periodic system. Indeed, almost everything is described in the cell: the serial number, which means electrons and protons, atomic mass (the average value of all existing isotopes of a given element). It can be seen in what period the structure is located (which means that electrons will be located on so many layers). You can also predict the number of negative particles at the last energy level for 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 protons from the mass number, that is, the serial number. Thus, it is possible to obtain and compose a whole electron-graphic formula for each chemical element, which will accurately reflect its structure and show possible oxidation states and manifest properties.
The distribution of elements in nature
A whole science is engaged in the study of this question - cosmochemistry. The data show that the distribution of elements on our planet repeats the same patterns in the universe. The main source of nuclei of light, heavy and medium atoms are nuclear reactions that occur in the bowels of stars - nucleosynthesis. Thanks to these processes, the Universe and outer space supplied our planet with all the available chemical elements.
In total, out of 118 known representatives in natural sources, 89 were discovered by people. These are the fundamental, most widespread atoms. Chemical elements were also synthesized artificially, by neutron bombardment of nuclei (nucleosynthesis in laboratory conditions).
The simplest substances of such elements as nitrogen, oxygen, hydrogen are considered the most numerous. Carbon is a part of all organic substances, which means it also occupies a leading position.
Classification by the electronic structure of atoms
One of the most common classifications of all chemical elements of a system is their distribution based on electronic structure. According to how many energy levels are included in the atomic shell and which of them contains the last valence electrons, four groups of elements can be distinguished.
S-elements
These are those in which the s-orbital is filled last. 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 that form the main subgroups from the third to the eighth group, relating to 3,4,5,6 periods. Among them, both metal and typical non-metallic elements are found by properties.
d-elements and f-elements
These are transition metals from 4 to 7 a large period. Only 32 items. Simple substances can exhibit both acidic and basic properties (oxidizing and reducing). Also amphoteric, that is, dual.
The f-family includes lanthanides and actinides, in which the latter electrons are located on f-orbitals.
Substances formed by elements: simple
Also, all classes of chemical elements are able to exist in the form of simple or complex compounds. So, it is considered to be simple that those that are formed from the same structure in different numbers. For example, O 2 is oxygen or oxygen, and O 3 is ozone. This phenomenon is called allotropy.
Simple chemical elements forming the compounds of the same name are characteristic of each representative of the periodic system. But not all of them are the same in terms of their properties. So, there are simple substances metals and non-metals. The first form the main subgroups with group 1-3 and all secondary subgroups in the table. Non-metals form the main subgroups of 4-7 groups. The eighth main includes special elements - noble or inert gases.
Among all the simple elements discovered today, under ordinary conditions, 11 gases, 2 liquid substances (bromine and mercury) are known, all the rest are solid.
Complex compounds
It is customary to include all those that consist of two or more chemical elements. There are many examples, because more than 2 million chemical compounds are known! These are salts, oxides, bases and acids, complex complexes, all organic substances.