A lot of different things and objects, living andthe inanimate bodies of nature surrounds us. And they all have their composition, structure, properties. The most complex biochemical reactions accompanying vital processes take place in living beings. Inanimate bodies perform various functions in the nature and life of biomass and have a complex molecular and atomic composition.
Но все вместе объекты планеты имеют общую peculiarity: they consist of a set of the smallest 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 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 understanding of the chemical elements -This is just a graphic display of atoms. The particles that make up everything that exists in the universe. That is, the question "what are chemical elements" can be given such an answer. These are complex small structures, sets of all isotopes of atoms, united by a common name, having their own graphic designation (symbol).
Today, 118 elements are knownwhich are open both in natural conditions 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 the name, and also plays 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 building molecules, simple and complex compounds, and therefore chemical interactions.
History of discovery
The very understanding of what chemicalelements came only in the XVII 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 alchemists dominated, recognizing the theory of four elements - Empidocles and Aristotle, as well as discovering the "combustible principles" (sulfur) and "metallic principles" (mercury).
Virtually the entire 18th century was spread.completely erroneous phlogiston theory. However, at the end of this period, Antoine Laurent Lavoisier proves that it is untenable. He repeats Boyle’s formulation, but at the same time complements 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 whatchemical elements, makes dalton. He is credited with the discovery of atomic mass. Based on this, he distributes a part of the known chemical elements in the order of increasing their atomic mass.
Stable intensive development of science and technologyallows you 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 Mendeleev - science became aware of the existence of 63 elements. The work of the Russian scientist was the first complete and permanently fixed classification of these particles.
The structure of the chemical elements at that timehas not been established. It was believed that the atom is indivisible, it is the smallest unit. With the discovery of the phenomenon of radioactivity, it was proved that it is divided into structural parts. Practically each of them exists in the form of several natural isotopes (of 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.
The system of chemical elements of the Mendeleev
The basis of the scientist put the difference in atomic massand managed in a brilliant way to arrange all the known chemical elements in order of increasing. However, the whole depth and genius of his scientific thinking and foresight lay in the fact that Mendeleev left empty spaces in his system, open cells for still unknown elements that, according to the scientist, will be discovered in the future.
And everything turned out exactly as he said.Over time, the chemical elements of the Mendeleev filled all the empty cells. Each predicted structure 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 chemical element system itselfdisplayed graphically by 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 (the main and secondary within each group). Most often, two rows of families — the lanthanides and actinides — are placed separately in the lower layers of the table.
Periodic system of Mendeleev contains all the necessary information about the chemical elements (serial number, mass number, name, sometimes the last layers of the electronic structure).
Item Names
The right to give a name is given tothe person who made the discovery of this chemical element. Many are named after planets (uranium, plutonium, neptunium). Another was given the name in honor of the great scientists (mendelevium, rutherford, copernium and others).
Often the elements are named after cities and countries(ruthenium, germanium, dubnium, francium, europium, and others). The promise even serves mythical heroes (promethium). Also common is the phenomenon when a particular name is given by the properties shown by simple and complex substances of a given element (hydrogen, oxygen, carbon).
Names are written in Latin, but in ourThere is a Russian translation of the country 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.
Characterization of atoms of chemical elements
Each representative of the periodic system hasits features both in structure and in the manifested properties. The characteristic of a chemical element consists of the analysis of the composition of its core and electronic layers, as well as 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 that determine its positive charge (p+1), as well as part of the atomic mass;
- neutrons that affect the mass number of an element and have no charge (n0).
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 on orbitals (s, p, d, and f), which form sublevels and levels (electron layers).
The atomic mass of the element consists of protons andneutrons, 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 electrically neutral, that is, having no charge at all, the number of negative electrons is always equal to the number of positive proton particles.
Thus, the chemical characteristicelement can be given by its position in the periodic system. Indeed, almost everything is described in the cell: the sequence 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 (it 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 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 ifsubtract from the mass number of protons, that is, the sequence number. Thus, it is possible to obtain and compose a whole electronic graphical 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 deals with the 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 nuclei of light, heavy and medium atoms are nuclear reactions occurring in the interior of stars - nucleosynthesis. Thanks to these processes, the Universe and outer space provided our planet with all the available chemical elements.
Всего из известных 118 представителей в natural sources of humans were found 89. These are the fundamental, most common atoms. Chemical elements were also synthesized artificially, by bombarding nuclei with neutrons (nucleosynthesis in the laboratory).
Simple substances of such elements as nitrogen, oxygen, hydrogen are considered to be the most numerous. Carbon is a component of all organic substances, and therefore also occupies a leading position.
Classification by the electronic structure of atoms
One of the most common classifications of allchemical elements of the system - is their distribution on the basis of electronic structure. According to how many energy levels are part of the shell of an atom and which of them contains the last valence electrons, four groups of elements can be distinguished.
S-elements
Это такие, у которых последней заполняется s-orbital. Elements of the first group of the main subgroup (or alkali metals) belong to this family. 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, belonging to 3,4,5,6 periods. Among them, by their properties, there are both metals and typical non-metallic elements.
d-elements and f-elements
These are transition metals from 4th to 7th big period.Only 32 elements. 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 last electrons are located on f-orbitals.
Substances formed by elements: simple
Also all classes of chemical elements are capableexist as simple or complex compounds. So, it is considered to be simple those that are formed from the same structure in different quantities. For example, O2 - oxygen or oxygen, and O3 - ozone. This phenomenon is called allotropy.
Simple chemical elements that formcompounds of the same name are characteristic of each representative of the periodic system. But not all of them are identical in their properties. So, there are simple substances metals and non-metals. The first ones form the main subgroups with 1-3 groups and all secondary subgroups in the table. Non-metals form the main subgroups of 4-7 groups. In the eighth main special elements - noble or inert gases.
Among all the simple elements currently open, under normal conditions, 11 gases, 2 liquid substances (bromine and mercury) are known, all the rest are solid.
Complex connections
These are usually attributed to all that areof two or more chemical elements. There are lots of examples, because there are more than 2 million known chemical compounds! These are salts, oxides, bases and acids, complex complex compounds, all organic substances.
