The sequence of atoms according to the increase in the charge of the nucleus and the filling of the outer electron shell with electrons.

The periodic system has seven periods. The first period, containing 2 elements, as well as the second and third, with 8 elements each, are called small. Other periods with 18 or more elements - big. The seventh period is over. The eighth period is not completed. The number of the period to which a chemical element belongs is determined by the number of its electron shells (energy levels).

Each period (with the exception of the first) begins with a typical metal ( , Na , , , , ) and ends with a noble gas ( , , , Xe , , ), which is preceded by a typical non-metal .

In the first period, in addition to helium, there is only one element - hydrogen, combining properties typical of both metals and (to a greater extent) non-metals. These elements are filled with electrons 1 s-subshell.

The elements of the second and third periods are filled sequentially s- and R-subshells. For elements of small periods, it is characteristic enough rapid increase electronegativity with increasing nuclear charges, weakening of metallic properties and strengthening of non-metallic ones.

The fourth and fifth periods contain decades of transitional d-elements (from scandium to zinc and from yttrium to cadmium), in which, after filling the external s-subshells are filled, according to the Klechkovsky rule, d-subshell of the previous energy level.

1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p 6f 7d 7f ...

In the sixth and seventh periods, saturation occurs 4 f- and 5 f-subshells, as a result of which they contain 14 more elements compared to the 4th and 5th periods (lanthanides in the sixth and actinides in the seventh period).

Due to the difference in periods in length and other features, there are different ways their relative position in the periodic table. In the short period version, small periods contain one row elements, large ones have two rows. In the long-term version, all periods consist of one series. The series of lanthanides and actinides are usually written separately at the bottom of the table.

Elements of the same period have similar atomic masses, but different physical and chemical properties, unlike elements of the same period.

Period - a row of the periodic system of chemical elements, a sequence of atoms in order of increasing nuclear charge and filling the outer electron shell with electrons.

The periodic system has seven periods. The first period, containing 2 elements, as well as the second and third, with 8 elements each, are called small. The remaining periods with 18 or more elements are large. The seventh period is not completed. The number of the period to which a chemical element belongs is determined by the number of its electron shells.

Each period begins with a typical metal and ends with a noble gas preceded by a typical non-metal.

In the first period, in addition to helium, there is only one element - hydrogen, which combines properties typical of both metals and non-metals. For these elements, the 1s subshell is filled with electrons.

The elements of the second and third periods have successive filling of s- and p-subshells. Elements of small periods are characterized by a fairly rapid increase in electronegativity with increasing nuclear charges, a weakening of metallic properties and an increase in non-metallic ones.

The fourth and fifth periods contain decades of transition d-elements, in which, after filling the outer s-subshell with electrons, the d-subshell of the previous energy level is filled, according to the Klechkovsky rule.

1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p 6f 7d 7f ...

In the sixth and seventh periods, the 4f- and 5f-subshells are saturated, as a result of which they contain 14 more elements compared to the 4th and 5th periods.

Due to the difference in periods in length and other features, there are different ways of their relative position in the periodic system. In the short-period version, small periods contain one row of elements each, large ones have two rows each. In the long-term version, all periods consist of one series. The series of lanthanides and actinides are usually written separately at the bottom of the table.

Elements of the same period have similar atomic masses, but different physical and chemical properties, unlike elements of the same group. With an increase in the nuclear charge of elements of the same period, the atomic radius decreases and the number of valence electrons increases, as a result of which the metallic and non-metallic properties of the elements are weakened, the reducing and oxidizing properties of the substances they form are weakened.

The fourth period of the periodic system includes elements of the fourth row (or fourth period) of the periodic system of chemical elements. The structure of the periodic table is based on lines to illustrate repeating (periodic) ... ... Wikipedia

The fifth period of the periodic system includes elements of the fifth row (or fifth period) of the periodic system of chemical elements. The structure of the periodic table is based on lines to illustrate recurring (periodic) trends in ... ... Wikipedia

The seventh period of the periodic system includes the elements of the seventh row (or the seventh period) of the periodic system of chemical elements. The structure of the periodic table is based on rows to illustrate repeating (periodic) trends ... Wikipedia

The sixth period of the periodic system includes the elements of the sixth row (or the sixth period) of the periodic system of chemical elements. The structure of the periodic table is based on lines to illustrate recurring (periodic) trends in ... ... Wikipedia

The first period of the periodic system includes the elements of the first row (or the first period) of the periodic system of chemical elements. The structure of the periodic table is based on lines to illustrate recurring (periodic) trends in ... ... Wikipedia

The second period of the periodic system includes elements of the second row (or second period) of the periodic system of chemical elements. The structure of the periodic table is based on rows to illustrate recurring (periodic) trends in ... Wikipedia

The third period of the periodic system includes elements of the third row (or third period) of the periodic system of chemical elements. The structure of the periodic table is based on rows to illustrate repeating (periodic) trends ... Wikipedia

Includes hypothetical chemical elements belonging to an additional eighth row (or period) of the periodic system. The systematized names of these elements are transferred to IUPAC for use. None of these elements has yet been ... ... Wikipedia

Period is a row of the periodic system of chemical elements, the sequence of atoms in order of increasing nuclear charge and filling the outer electron shell with electrons. The periodic system has seven periods. The first period containing 2 elements ... Wikipedia

The short form of the periodic table is based on the parallelism of the oxidation states of the elements of the main and secondary subgroups: for example, the maximum oxidation state of vanadium is +5, like that of phosphorus and arsenic, the maximum oxidation state of chromium is +6 ... Wikipedia

Books

• S. Yu. Witte. Collected works and documentary materials. In 5 volumes. Volume 3. Book 2, S. Yu. Witte. The second book of the third volume of the publication includes the most important documentary materials, official notes, publications and articles on the monetary reform and the monetary system in Russia, which amounted to ...
• Periodical press and censorship of the Russian Empire in 1865-1905. The system of administrative penalties, . The book examines the censorship policy of the Russian government in relation to the periodical press at a time when the role of the latter in the life of society was becoming increasingly influential.…

Period - a row of the periodic system of chemical elements, a sequence of atoms in order of increasing nuclear charge and filling the outer electron shell with electrons.

The periodic system has seven periods. The first period, containing 2 elements, as well as the second and third, with 8 elements each, are called small. The remaining periods with 18 or more elements are large. The seventh period is not completed. The number of the period to which a chemical element belongs is determined by the number of its electron shells (energy levels).

The charge number of the atomic nucleus (synonyms: atomic number, atomic number, ordinal number of a chemical element) is the number of protons in the atomic nucleus. The charge number is equal to the charge of the nucleus in units of elementary charge and at the same time is equal to the ordinal number of the chemical element corresponding to the nucleus in the periodic table.

The group of the periodic system of chemical elements is a sequence of atoms in increasing nuclear charge that have the same electronic structure.

In the short period version of the periodic system, the groups are divided into subgroups - the main (or subgroups A), starting with elements of the first and second periods, and side (subgroups B), containing d-elements. Subgroups are also named after the element with the smallest nuclear charge (usually the element of the second period for the main subgroups and the element of the fourth period for the secondary subgroups). Elements of the same subgroup have similar chemical properties.

what is a period in chemistry

1. Period is a row of the periodic system of chemical elements, the sequence of atoms in order of increasing nuclear charge and filling the outer electron shell with electrons.

   The periodic system has seven periods. The first period, containing 2 elements, as well as the second and third, with 8 elements each, are called small. The remaining periods with 18 or more elements are large. The seventh period is not completed. The number of the period to which a chemical element belongs is determined by the number of its electron shells (energy levels).

   
   

   Each period (except the first) begins with a typical metal (Li, Na, K, Rb, Cs, Fr) and ends with a noble gas (He, Ne, Ar, Kr, Xe, Rn), preceded by a typical non-metal.

   Dawn#769;double number#769; atomic nucleus (synonyms: atomic number, atomic number, ordinal number of a chemical element) the number of protons in the atomic nucleus. The charge number is equal to the charge of the nucleus in units of elementary charge and at the same time is equal to the ordinal number of the chemical element corresponding to the nucleus in the periodic table.

   The group of the periodic system of chemical elements is a sequence of atoms in ascending order of the charge of the nucleus, which have the same electronic structure.

   The group number is determined by the number of electrons on the outer shell of the atom (valence electrons) and, as a rule, corresponds to the highest valency of the atom.

   In the short period version of the periodic system, the groups are divided into main subgroups (or subgroups A), starting with elements of the first and second periods, and secondary (subgroups B), containing d-elements. Subgroups are also named after the element with the smallest nuclear charge (usually the element of the second period for the main subgroups and the element of the fourth period for the secondary subgroups). Elements of the same subgroup have similar chemical properties.

   With an increase in the nuclear charge of the elements of the same group, due to an increase in the number of electron shells, atomic radii increase, as a result of which there is a decrease in electronegativity, an increase in the metallic and weakening of the non-metallic properties of the elements, an increase in the reduction and weakening of the oxidizing properties of the substances they form.

2. Horizontal lines in the table. Mendeleev
3. Horizontal line (that sho zleva) tab. Mendelev

Evolution of the Periodic Table of Chemical Elements

The idea introduced by Mendeleev about the place of an element in the system turned out to be special and important for the evolution of the periodic system of chemical elements; the position of the element is determined by the period and group numbers. Based on this idea, Mendeleev came to the conclusion that it was necessary to change the then accepted atomic weights of some elements (U, In, Ce and its analogues), which was the first practical use P. s. e., and also for the first time predicted the existence and basic properties of several unknown elements, which corresponded to the empty cells of P. s. e. A classic example is the prediction of "ekaaluminum" (the future Ga, discovered by P. Lecoq de Boisbaudran in 1875), "ecabor" (Sc, discovered by the Swedish scientist L. Nilsson in 1879) and "ecasilicium" (Ge, discovered by the German scientist K. Winkler in 1886). In addition, Mendeleev predicted the existence of analogues of manganese (future Tc and Re), tellurium (Po), iodine (At), cesium (Fr), barium (Ra), tantalum (Pa).

In many ways, it represented an empirical generalization of facts, since the physical meaning of the periodic law was unclear and there was no explanation for the reasons for the periodic change in the properties of elements depending on the increase in atomic weights.

up to the physical substantiation of the periodic law and the development of the theory of P. s. e. many facts could not be explained. So, unexpected was the discovery at the end of the 19th century. inert gases, which seemed to find no place in P. s. e.; this difficulty was eliminated thanks to inclusion in P. of page. e. independent zero group (subsequently VIIIa-subgroup). The discovery of many "radio elements" at the beginning of the 20th century. led to the contradiction between necessity of their placement in P. of page. e. and its structure (for more than 30 such elements, there were 7 "vacant" places in the sixth and seventh periods). This contradiction was overcome as a result of the discovery of isotopes. Finally, the value of the atomic weight (atomic mass) as a parameter that determines the properties of elements gradually lost its significance.

The structure of the periodic system of chemical elements.

Modern (1975) P. s. e. covers 106 chemical elements; of these, all transuranium (Z = 93-106), as well as elements with Z = 43 (Tc), 61 (Pm), 85 (At) and 87 (Fr) were obtained artificially. For the entire history of P. s. e. a large number (several hundred) of variants of its graphic image, mainly in the form of tables; images are also known in the form of various geometric figures (spatial and planar), analytical curves (for example, spirals), etc. The most widespread are three forms of P.

e .: short, proposed by Mendeleev (Fig. 2) and received universal recognition (in its modern form it is given in the illustration); long (Fig. 3); staircase (Fig. 4). The long form was also developed by Mendeleev, and in an improved form it was proposed in 1905 by A. Werner. The ladder form was proposed by the English scientist T. Bailey (1882), the Danish scientist J. Thomsen (1895) and improved by N. Bohr (1921). Each of the three forms has advantages and disadvantages. The fundamental principle of constructing P. s. e. is the division of all chemical elements into groups and periods. Each group, in turn, is divided into the main (a) and secondary (b) subgroups. Each subgroup contains elements that have similar chemical properties. The elements of the a- and b-subgroups in each group, as a rule, show a certain chemical similarity among themselves, mainly in higher oxidation states, which, as a rule, correspond to the group number. A period is a set of elements starting with an alkali metal and ending with an inert gas (a special case is the first period); Each period contains a strictly defined number of elements. P. s. e. consists of 8 groups and 7 periods (the seventh has not yet been completed).

First Period of the Periodic Table of the Elements

The specificity of the first period is that it contains only 2 elements: H and He. The place of H in the system is ambiguous: hydrogen exhibits properties common with alkali metals and halogens, it is placed either in the Ia- or (more preferably) in the VIIa-subgroup. Helium is the first representative of the VIIa subgroup (however for a long time Not all inert gases were combined into an independent zero group).

Second Period of the Periodic Table of the Elements

The second period (Li - Ne) contains 8 elements. It begins with the alkali metal Li, whose only oxidation state is I. Then comes Be, a metal, oxidation state II. The metallic nature of the next element B is weakly expressed (oxidation state III). The C following it is a typical non-metal, it can be both positively and negatively tetravalent. The subsequent N, O, F and Ne are non-metals, and only N has the highest oxidation state V corresponding to the group number; oxygen only in rare cases exhibits a positive valency, and for F, the oxidation state VI is known. The period is completed by the inert gas Ne.

Third Period of the Periodic Table of the Elements

The third period (Na - Ar) also contains 8 elements, the nature of the change in the properties of which is largely similar to that observed in the second period. However, Mg, unlike Be, is more metallic, as is Al compared to B, although Al is inherently amphoteric. Si, P, S, Cl, Ar are typical non-metals, but all of them (except Ar) exhibit higher degrees oxidations equal to the group number. Thus, in both periods, as Z increases, a weakening of the metallic and strengthening of the non-metallic nature of the elements is observed. Mendeleev called the elements of the second and third periods (small, in his terminology) typical. It is significant that they are among the most common in nature, and C, N and O, along with H, are the main elements of organic matter (organogens). All elements first three periods are included in subgroups a.

Modern terminology - the elements of these periods refer to the s-elements (alkali and alkaline earth metals) that make up the Ia- and IIa-subgroups (highlighted in red on the color table), and the p-elements (B - Ne, At - Ar), included in IIIa - VIIIa-subgroups (their symbols are highlighted orange). For elements of small periods with increasing serial numbers first, a decrease in atomic radii is observed, and then, when the number of electrons in the outer shell of the atom already increases significantly, their mutual repulsion leads to an increase in atomic radii. The next maximum is reached at the beginning of the next period on an alkaline element. Approximately the same regularity is typical for ionic radii.

Fourth Period of the Periodic Table of the Elements

The fourth period (K - Kr) contains 18 elements (the first large period, according to Mendeleev). After the alkali metal K and the alkaline earth Ca (s-elements), there follows a series of ten so-called transition elements (Sc - Zn), or d-elements (symbols are given in blue), which are included in subgroups b of the corresponding groups of P. s. e. Most transition elements (all of them metals) exhibit higher oxidation states equal to the group number. The exception is the triad Fe - Co - Ni, where the last two elements are maximally positively trivalent, and iron in certain conditions known in oxidation state VI. Elements starting from Ga and ending with Kr (p-elements) belong to subgroups a, and the nature of the change in their properties is the same as in the corresponding intervals Z for elements of the second and third periods. It has been established that Kr is able to form chemical compounds (mainly with F), but the oxidation state VIII is unknown for it.

Fifth Period of the Periodic Table of the Elements

The fifth period (Rb - Xe) is constructed similarly to the fourth; it also has an insert of 10 transition elements (Y - Cd), d-elements. Specific features of the period: 1) in the triad Ru - Rh - Pd, only ruthenium exhibits oxidation state VIII; 2) all elements of subgroups a show the highest oxidation states equal to the group number, including Xe; 3) I has weak metallic properties. Thus, the nature of the change in properties as Z increases for the elements of the fourth and fifth periods is more complicated, since the metallic properties are preserved in a large range of serial numbers.

Sixth Period of the Periodic Table of the Elements

The sixth period (Cs - Rn) includes 32 elements. In addition to 10 d-elements (La, Hf - Hg), it contains a set of 14 f-elements, lanthanides, from Ce to Lu (black symbols). The elements La to Lu are chemically very similar. In short form P. s. e. the lanthanides are included in the box La (because their predominant oxidation state is III) and are listed on a separate line at the bottom of the table. This technique is somewhat inconvenient, since 14 elements are, as it were, outside the table. The long and ladder forms P. of page are deprived of a similar lack. e., well reflecting the specifics of lanthanides against the background of the integral structure of P. s. e. Features of the period: 1) in the triad Os - Ir - Pt, only osmium exhibits oxidation state VIII; 2) At has a more pronounced (compared to 1) metallic character; 3) Rn, apparently (its chemistry is little studied), should be the most reactive of the inert gases.

If the periodic table seems difficult for you to understand, you are not alone! Although it can be difficult to understand its principles, learning to work with it will help in the study of natural sciences. To get started, study the structure of the table and what information can be learned from it about each chemical element. Then you can start exploring the properties of each element. And finally, using the periodic table, you can determine the number of neutrons in an atom of a particular chemical element.

Steps

Part 1

Table structure

The periodic table, or the periodic table of chemical elements, begins at the left upper corner and ends at the end of the last row of the table (lower right corner). The elements in the table are arranged from left to right in ascending order of their atomic number. The atomic number tells you how many protons are in one atom. In addition, as the atomic number increases, so does the atomic mass. Thus, by the location of an element in the periodic table, you can determine its atomic mass.

1. As you can see, each next element contains one more proton than the element that precedes it. This is obvious when you look at the atomic numbers. Atomic numbers increase by one as you move from left to right. Since the elements are arranged in groups, some table cells remain empty.

   • For example, the first row of the table contains hydrogen, which has atomic number 1, and helium, which has atomic number 2. However, they are on opposite ends because they belong to different groups.

2. Learn about groups that include elements with similar physical and chemical properties. The elements of each group are located in the corresponding vertical column. As a rule, they are indicated by the same color, which helps to identify elements with similar physical and chemical properties and predict their behavior. All elements of a particular group have the same number of electrons in the outer shell.

   • Hydrogen can be attributed both to the group of alkali metals and to the group of halogens. In some tables it is indicated in both groups.
   • In most cases, the groups are numbered from 1 to 18, and the numbers are placed at the top or bottom of the table. Numbers can be given in Roman (eg IA) or Arabic (eg 1A or 1) numerals.
   • When moving along the column from top to bottom, they say that you are "browsing the group".

3. Find out why the table contains empty cells. Elements are ordered not only according to their atomic number, but also according to groups (elements of the same group have similar physical and chemical properties). This makes it easier to understand how an element behaves. However, as the atomic number increases, elements that fall into the corresponding group are not always found, so there are empty cells in the table.

   • For example, the first 3 rows have empty cells, since transition metals are found only from atomic number 21.
   • Elements with atomic numbers from 57 to 102 belong to the rare earth elements, and they are usually placed in a separate subgroup in the lower right corner of the table.

4. Each row of the table represents a period. All elements of the same period have the same number of atomic orbitals in which electrons are located in atoms. The number of orbitals corresponds to the period number. The table contains 7 rows, that is, 7 periods.

   • For example, the atoms of the elements of the first period have one orbital, and the atoms of the elements of the seventh period have 7 orbitals.
   • As a rule, periods are indicated by numbers from 1 to 7 on the left of the table.
   • As you move along a line from left to right, you are said to be "scanning through a period".

5. Learn to distinguish between metals, metalloids and non-metals. You will better understand the properties of an element if you can determine what type it belongs to. For convenience, in most tables, metals, metalloids and non-metals are indicated by different colors. Metals are on the left, and non-metals are on the right side of the table. Metalloids are located between them.

   Part 2

   Element designations

   1. Each element is designated by one or two Latin letters. As a rule, the element symbol is given capital letters in the center of the corresponding cell. A symbol is an abbreviated name for an element that is the same in most languages. When doing experiments and working with chemical equations, the symbols of the elements are commonly used, so it is useful to remember them.

      • Typically, element symbols are shorthand for their Latin name, although for some, especially recently discovered elements, they are derived from the common name. For example, helium is denoted by the symbol He, which is close to the common name in most languages. At the same time, iron is designated as Fe, which is an abbreviation of its Latin name.

   2. Pay attention to the full name of the element, if it is given in the table. This "name" of the element is used in normal texts. For example, "helium" and "carbon" are the names of the elements. Usually, though not always, the full names of the elements are given under their chemical symbol.

      • Sometimes the names of the elements are not indicated in the table and only their chemical symbols are given.

   3. Find the atomic number. Usually the atomic number of an element is located at the top of the corresponding cell, in the middle or in the corner. It can also appear below the symbol or element name. Elements have atomic numbers from 1 to 118.

      • The atomic number is always an integer.

   4. Remember that the atomic number corresponds to the number of protons in an atom. All atoms of an element contain the same number of protons. Unlike electrons, the number of protons in the atoms of an element remains constant. Otherwise, another chemical element would have turned out!

      • The atomic number of an element can also be used to determine the number of electrons and neutrons in an atom.

   5. Usually the number of electrons is equal to the number of protons. The exception is the case when the atom is ionized. Protons have a positive charge and electrons have a negative charge. Since atoms are usually neutral, they contain the same number of electrons and protons. However, an atom can gain or lose electrons, in which case it becomes ionized.

      • Ions have electric charge. If there are more protons in the ion, then it has a positive charge, in which case a plus sign is placed after the element symbol. If an ion contains more electrons, it has a negative charge, which is indicated by a minus sign.
      • The plus and minus signs are omitted if the atom is not an ion.