The year in which Mendeleev formulated the periodic law. D. Mendeleev's periodic law, its modern formulation. What is its difference from the one given by D.I. Mendeleev? Explain what caused such a change in the wording of the law? What is zak
Periodic law- the basic law of chemistry - was discovered in 1869 year DI. Mendeleev. At that time, the atom was still considered indivisible and nothing was known about its internal structure.
Atomic masses(then - atomic weights) and the chemical properties of the elements were taken as the basis Periodic law D.I. Mendeleev. DI. Mendeleev, arranging 63 elements known at that time in the order of increasing their atomic masses, received natural (natural) number of chemical elements, where he noted the periodic recurrence of chemical properties. For example, a typical non-metal fluorine F repeated for the elements chlorine Cl, bromine Br, iodine I, typical metal properties lithium Li - the elements sodium Na and potassium K etc.
For some elements D.I. Mendeleev did not find chemical analogues (in aluminum Al and silicon Si, for example), in the Sioux of the fact that at that time such analogs were not yet known. In the table they were intended empty spaces, but based on periodic repeatability the scientist predicted their chemical properties). After the discovery of the corresponding elements of prediction by D.I. Mendeleev was completely confirmed (analogue of aluminum - gallium Ga, silicon analog - germanium Ge).
The periodic law as formulated by D.I. Mendeleev is presented as follows: in periodic dependence on the value of the atomic weights of elements, there are the properties of simple bodies, as well as the shapes and properties of compounds of elements.
The modern formulation of the Periodic Law of D.I. Mendeleev sounds like this: the properties of the elements are periodically dependent on the ordinal number.
Periodic law of D.I. Mendeleev became the basis for the creation of scientists Periodic table of chemical elements... She is presented 7 periods and 8 in groups.
Periods horizontal rows of the table are called, which are divided into small and large. 2 elements (1st period) or 8 elements (2nd, 3rd periods) are in small periods, and in large periods there are 18 elements (4th, 5th periods) or 32 elements (6th period), the 7th period is still incomplete. Every period begins with a typical metal from Ends with a typical non-metal and noble gas.
By groups elements are called vertical columns. Each group is represented by two subgroups - the main and collateral... A subgroup is a set of elements that are complete chemical analogs; often the elements of a subgroup have the highest oxidation state corresponding to the group number. For example, the highest oxidation state (+ II) corresponds to elements of the subgroup beryllium and zinc(main and secondary subgroups of group II), and elements of the subgroup nitrogen and vanadium(V group) corresponds to the highest oxidation state (+ V).
The chemical properties of elements in the main subgroups can vary from non-metallic to metallic (in the main subgroup of group V, nitrogen is a non-metal, and bismuth is a metal) - over a wide range. The properties of elements in secondary subgroups change, but not so dramatically; for example, elements of the side group IV of group - zirconium, titanium, hafnium- are very similar in their properties (especially zirconium and hafnium).
In the Periodic Table in Group I (Li - Fr), II (Mg - Ra) and III (In, Tl) typical metals are located. Non-metals are located in groups VII (F - At), VI (O - Te), V (N - As), IV (C, Si) and III (B). Some elements of the main groups ( Be, Al, Ge, Sb, Po), as well as many elements of side groups can exhibit both metallic and non-metallic properties. This phenomenon is called amphotericity.
For some main groups, groups are used 
new names: VIII (Not - Rn) - noble gases, VII (F - At) - halogens, IV (O - Ro) - chalcogenes, II (Ca - Ra) - alkaline earth metals, I (Li - Fr) - alkali metals.
The form of the Periodic System, which was proposed by D.I. Mendeleev, was named short-period, or classical... In modern chemistry, another form is increasingly used - long-period, in which all periods - small and large - are stretched out in long rows, starting with an alkali metal and ending with a noble gas.
Periodic law of D.I. Mendeleev and the Periodic Table of Elements by D.I. Mendeleev became the basis of modern chemistry.
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As a result of successful mastering of the material in this chapter, the student should:
know
- modern formulation of the periodic law;
- connection between the structure of the periodic system and the energy sequence of sublevels in many-electron atoms;
- definitions of the concepts "period", "group", "5-elements", "p-elements", "D- elements "," / -elements "," ionization energy "," electron affinity "," electronegativity "," van der Waals radius "," clarke ";
- the basic law of geochemistry;
be able to
Describe the structure of the periodic table in accordance with Klechkovsky's rules;
own
Ideas about the periodic nature of changes in the properties of atoms and the chemical properties of elements, about the features of the long-period version of the periodic system; about the relationship between the prevalence of chemical elements with their position in the periodic system, about macro- and microelements in the lithosphere and living matter.
Modern formulation of the periodic law
Periodic law - the most general law of chemistry was discovered by Dmitry Ivanovich Mendeleev in 1869. At that time, the structure of the atom was not yet known. DI Mendeleev made his discovery based on the regular change in the properties of elements with an increase in atomic masses.
After the discovery of the structure of atoms, it became clear that their properties are determined by the structure of the electron shells, which depends on the total number of electrons in the atom. The number of electrons in an atom is equal to the charge of its nucleus. Therefore, the modern formulation of the periodic law is as follows.
The properties of chemical elements and the simple and complex substances formed by them are periodically dependent on the charge of the nucleus of their atoms.
The significance of the periodic law lies in the fact that it is the main tool for systematizing and classifying chemical information, a very important means of interpreting and interpreting chemical information, a powerful tool for predicting the properties of chemical compounds and a means of directed search for compounds with predetermined properties.
The periodic law does not have a mathematical expression in the form of equations, it is reflected in the table, which is called the periodic system of chemical elements. There are many variations of the periodic table tables. The most widespread are the long-period and short-period versions, which are placed on the first and second color inserts of the book. The main structural unit of the periodic system is the period.
Period numbered is called a sequence of chemical elements arranged in the order of increasing charge of the atomic nucleus, which begins with ^ -elements and ends with ^ -elements.
In this definition NS - period number equal to the main quantum number for the upper energy level in the atoms of all elements of this period. In atoms s-elements 5-sublevels are completed, in atoms p-elements - respectively p-sublevels. An exception to the above definition is the first period in which there are no p-elements, since at the first energy level (n = 1) there is only 15-nodal level. The periodic table also contains d-elements for which the ^ -sublevels are completed, and / -elements, for which / -sub-levels are completed.
In 1871 Mendeleev's periodic law was formulated. By this time, 63 elements were known to science, and Dmitry Ivanovich Mendeleev ordered them on the basis of relative atomic mass. The modern periodic table has expanded significantly.
History
In 1869, while working on a chemistry textbook, Dmitry Mendeleev faced the problem of systematizing the material accumulated over many years by various scientists - his predecessors and contemporaries. Even before Mendeleev's work, attempts were made to systematize the elements, which served as prerequisites for the development of the periodic system.
Rice. 1. Mendeleev D.I ..
Element classification searches are summarized in the table.
Mendeleev ordered the elements according to their relative atomic mass, arranging them in ascending order. There are nineteen horizontal and six vertical rows in total. This was the first edition of the periodic table of the elements. This is the beginning of the history of the discovery of the periodic law.
It took the scientist almost three years to create a new, more perfect table. Six columns of elements turned into horizontal periods, each of which began with an alkali metal and ended with a non-metal (inert gases were not yet known). The horizontal rows formed eight vertical groups.
Unlike his colleagues, Mendeleev used two criteria for the distribution of elements:
- atomic mass;
- Chemical properties.
It turned out that there is a pattern between these two criteria. After a certain number of elements with increasing atomic mass, the properties begin to repeat themselves.
Rice. 2. The table compiled by Mendeleev.
Initially, the theory was not expressed mathematically and could not be fully confirmed experimentally. The physical meaning of the law became clear only after the creation of the atomic model. The idea is to repeat the structure of the electron shells with a sequential increase in the charges of the nuclei, which is reflected in the chemical and physical properties of the elements.
Law
Having established the periodicity of changes in properties with an increase in atomic mass, Mendeleev in 1871 formulated the periodic law, which became fundamental in chemical science.
Dmitry Ivanovich determined that the properties of simple substances are periodically dependent on the relative atomic masses.
The science of the 19th century did not have modern knowledge about the elements, therefore the modern formulation of the law is somewhat different from Mendeleev's. However, the essence remains the same.
With the further development of science, the structure of the atom was studied, which influenced the formulation of the periodic law. According to the modern periodic law, the properties of chemical elements depend on the charges of atomic nuclei.
table
Since the time of Mendeleev, the table he created has significantly changed and began to reflect almost all the functions and characteristics of the elements. The ability to use the table is essential for further study of chemistry. The modern table is presented in three forms:
- short - periods occupy two lines, and hydrogen is often referred to as group 7;
- long - isotopes and radioactive elements are taken out of the table;
- extra-long - each period occupies a separate line.
Rice. 3. Long modern table.
The short table is the most obsolete version that was canceled in 1989, but is still used in many textbooks. The long and extra long shapes are internationally recognized and used all over the world. Despite the established forms, scientists continue to improve the periodic system, offering the latest options.
What have we learned?
Mendeleev's periodic law and periodic system were formulated in 1871. Mendeleev identified the regularities of the properties of elements and ordered them on the basis of the relative atomic mass. As the mass increased, the properties of the elements changed and then repeated. Subsequently, the table was supplemented, and the law was adjusted in accordance with modern knowledge.
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The properties of chemical elements and their compounds are in periodic dependence on the value of the charge of the nuclei of their atoms, which is expressed in the periodic recurrence of the structure of the outer valence electron shell.
And now, more than 130 years after the discovery of the periodic law, we can return to the words of Dmitry Ivanovich, taken as the motto of our lesson: "The future does not threaten the periodic law with destruction, but only the superstructure and development are promised." How many chemical elements have been discovered at the moment? And this is far from the limit.
The graphical representation of the periodic law is the periodic table of chemical elements. This is a short synopsis of the entire chemistry of the elements and their compounds.
Changes in properties in the periodic table with an increase in the value of atomic weights in the period (from left to right):
1. Metallic properties decrease
2. Non-metallic properties increase
3. The properties of higher oxides and hydroxides vary from basic through amphoteric to acidic.
4. The valence of elements in the formulas of higher oxides increases from I to VII, and in the formulas of volatile hydrogen compounds decreases from IV to I.
Basic principles of constructing the periodic system.
| Basic principles of constructing the periodic system. Comparison attribute | D.I. Mendeleev | State of the art |
| 1. How is the sequence of elements by numbers established? (What is the basis of the PS?) 2. The principle of combining elements into groups. 3. The principle of combining elements into periods. | The elements are arranged in order of increasing relative atomic masses. However, there are exceptions. Qualitative trait. The similarity of the properties of simple substances and complex ones of the same type. The set of elements as the relative atomic mass increases from one alkali metal to another. | The elements are arranged as the charge of the nuclei of their atoms grows. There are no exceptions. Quantitative trait. The similarity of the structure of the outer shell. The periodic recurrence of the structure of the outer shell determines the similarity of chemical properties. Each new period begins with the appearance of a new electron layer with one electron. And this is always an alkali metal. |
The periodic table is a graphic representation of the periodic law. It contains 7 periods and 8 groups.
1. Serial number of a chemical element- the number given to the element when it is numbered. Shows the total number of electrons in an atom and the number of protons in the nucleus, determines the charge of the nucleus of an atom of a given chemical element.
2. Period- chemical elements arranged in a line (only 7 periods). The period determines the number of energy levels in the atom.
Small periods (1 - 3) include only s- and p-elements (elements of the main subgroups) and consist of one line; large (4 - 7) include not only s- and p-elements (elements of the main subgroups), but also d- and f-elements (elements of secondary subgroups) and consist of two lines.
3. Groups- chemical elements arranged in a column (there are only 8 groups). The group determines the number of electrons at the outer level for the elements of the main subgroups, as well as the number of valence electrons in the atom of a chemical element.
Main subgroup (A)- includes elements of large and small periods (only s- and p-elements).
Side subgroup (B)- includes elements of only large periods (only d- or f-elements).
