On the correlation of the laws of periodicity of element nuclei. The difference between the classical and modern formulation of Mendeleev's periodic law. Periodic properties of elements

Periodic law D.I. Mendeleev:Properties of simple bodies, as well as shapes and properties of compoundsdifferences of elements are periodically dependent onthe values ​​of the atomic weights of elements. (The properties of elements are periodically dependent on the charge of the atoms of their nuclei).

Periodic table of elements. Series of elements within which properties change sequentially, such as the series of eight elements from lithium to neon or from sodium to argon, Mendeleev called periods. If we write these two periods one below the other so that sodium is under lithium and argon is under neon, we get the following arrangement of elements:

With this arrangement, elements that are similar in their properties and have the same valency, for example, lithium and sodium, beryllium and magnesium, etc., fall into the vertical columns.

Having divided all the elements into periods and placing one period under another so that elements similar in properties and type of compounds formed were located under each other, Mendeleev compiled a table that he called the periodic system of elements by groups and series.

The meaning of the periodic systemWe. The periodic table of elements had a great influence on the subsequent development of chemistry. Not only was it the first natural classification chemical elements, which showed that they form a coherent system and are in close connection with each other, but also became a powerful tool for further research.

7. Periodic changes in the properties of chemical elements. Atomic and ionic radii. Ionization energy. Electron affinity. Electronegativity.

The dependence of atomic radii on the charge of the nucleus of an atom Z is periodic. Within one period, as Z increases, there is a tendency for the size of the atom to decrease, which is especially clearly observed in short periods

With the beginning of the construction of a new electronic layer, more distant from the nucleus, i.e., during the transition to the next period, atomic radii increase (compare, for example, the radii of fluorine and sodium atoms). As a result, within a subgroup, with increasing nuclear charge, the sizes of atoms increase.

The loss of electron atoms leads to a decrease in its effective size, and the addition of excess electrons leads to an increase. Therefore, the radius of a positively charged ion (cation) is always smaller, and the radius of a negatively charged non (anion) is always greater than the radius of the corresponding electrically neutral atom.

Within one subgroup, the radii of ions of the same charge increase with increasing nuclear charge. This pattern is explained by an increase in the number of electronic layers and the growing distance of outer electrons from the nucleus.

The most characteristic chemical property of metals is the ability of their atoms to easily give up external electrons and transform into positively charged ions, while non-metals, on the contrary, are characterized by the ability to add electrons to form negative ions. To remove an electron from an atom and transform the latter into a positive ion, it is necessary to expend some energy, called ionization energy.

Ionization energy can be determined by bombarding atoms with electrons accelerated in an electric field. The lowest field voltage at which the electron speed becomes sufficient to ionize atoms is called the ionization potential of the atoms of a given element and is expressed in volts. With the expenditure of sufficient energy, two, three or more electrons can be removed from an atom. Therefore, they speak of the first ionization potential (the energy of the removal of the first electron from the atom) and the second ionization potential (the energy of the removal of the second electron)

As noted above, atoms can not only donate, but also gain electrons. The energy released when an electron attaches to a free atom is called the atom's electron affinity. Electron affinity, like ionization energy, is usually expressed in electron volts. Thus, the electron affinity of the hydrogen atom is 0.75 eV, oxygen - 1.47 eV, fluorine - 3.52 eV.

The electron affinities of metal atoms are typically close to zero or negative; It follows from this that for atoms of most metals the addition of electrons is energetically unfavorable. The electron affinity of nonmetal atoms is always positive and the greater, the closer the nonmetal is located to the noble gas in the periodic table; this indicates an increase in non-metallic properties as the end of the period approaches.

As a result of successfully mastering 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 multielectron atoms;
• definitions of the concepts “period”, “group”, “5-elements”, “p-elements”, "d- elements", "/-elements", "ionization energy", "electron affinity", "electronegativity", "van der Waals radius", "clark";
• basic law of geochemistry;

be able to

Describe the structure of the periodic table in accordance with Klechkovsky's rules;

own

Concepts about the periodic nature of changes in the properties of atoms and chemical properties elements, about the features of the long-period version of the periodic system; about the connection between the prevalence of chemical elements and their position in the periodic table, 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. D.I. Mendeleev made his discovery based on the natural change in the properties of elements with increasing atomic masses.

After the discovery of the structure of atoms, it became clear that their properties are determined by the structure electronic 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 they form periodically depend on the charge of the nucleus of their atoms.

The significance of the periodic law is that it is the main tool for systematizing and classifying chemical information, very important means interpretation, interpretation of chemical information, a powerful tool for predicting properties chemical compounds and a means of targeted search for compounds with predetermined properties.

The periodic law does not have a mathematical expression in the form of equations; it is reflected in a table called periodic system of chemical elements. There are many variations of periodic table tables. The most widely used are the long-period and short-period versions, placed on the first and second color inserts of the book. The main structural unit of the periodic system is the period.

Period number n is a sequence of chemical elements arranged in order of increasing charge of the atomic nucleus, which begins with ^-elements and ends with ^-elements.

In this definition p - period number equal to the principal quantum number for the upper energy level in the atoms of all elements of this period. In atoms s-elements 5-sublevels are being completed, in atoms p-elements - respectively p-sublevels. The exception to the above definition is the first period, which has no p-elements, since in the first energy level (n = 1) there is only a 15-level. The periodic table also contains d-elements, for which ^-sublevels are completed, and /-elements, for which /-sublevels are being completed.

The periodic law of chemical elements is a fundamental law of nature that establishes the periodicity of changes in the properties of chemical elements as the charges of the nuclei of their atoms increase. The date of discovery of the law is considered to be March 1 (February 17, old style) 1869, when D. I. Mendeleev completed the development of the “Experience of a system of elements based on their atomic weight and chemical similarity.” The scientist first used the term “periodic law” (“law of periodicity”) at the end of 1870. According to Mendeleev, “three types of data” contributed to the discovery of the periodic law. Firstly, there is enough availability large number known elements (63); secondly, satisfactory knowledge of the properties of most of them; thirdly, the fact that the atomic weights of many elements were determined with good accuracy, thanks to which chemical elements could be arranged in a natural series in accordance with the increase in their atomic weights. Mendeleev considered the decisive condition for the discovery of the law to be the comparison of all elements according to their atomic weights (previously only chemically similar elements were compared).

The classical formulation of the periodic law, given by Mendeleev in July 1871, stated: “The properties of the elements, and therefore the properties of the simple and complex bodies they form, are periodically dependent on their atomic weight.” This formulation remained in force for more than 40 years, but the periodic law remained only a statement of facts and had no physical basis. It became possible only in the mid-1910s, when the nuclear-planetary model of the atom was developed (see Atom) and it was established that serial number element in the periodic table is numerically equal to the charge of the nucleus of its atom. As a result, the physical formulation of the periodic law became possible: “Properties of elements and the simple and complex substances are periodically dependent on the nuclear charges (Z) of their atoms.” It is still widely used today. The essence of the periodic law can be expressed in other words: “The configurations of the outer electron shells of atoms are periodically repeated as Z increases”; This is a kind of “electronic” formulation of the law.

An essential feature of the periodic law is that, unlike some other fundamental laws of nature (for example, the law universal gravity or the law of equivalence of mass and energy), it does not have a quantitative expression, that is, it cannot be written in the form of any mathematical formula or equation. Meanwhile, Mendeleev himself and other scientists tried to look for a mathematical expression of the law. Various patterns of construction can be quantitatively expressed in the form of formulas and equations electronic configurations atoms depending on the values ​​of the principal and orbital quantum numbers. As for the periodic law, it has a clear graphical reflection in the form of a periodic system of chemical elements, represented mainly various types tables.

The periodic law is a universal law for the entire Universe, manifesting itself wherever material structures of the atomic type exist. However, it is not only the configurations of atoms that periodically change as Z increases. It turned out that the structure and properties atomic nuclei also change periodically, although the character itself periodic change here it is much more complicated than in the case of atoms: in the nuclei there is a regular construction of proton and neutron shells. Nuclei in which these shells are filled (they contain 2, 8, 20, 50, 82, 126 protons or neutrons) are called “magic” and are considered as a kind of boundaries of the periods of the periodic system of atomic nuclei.

Alchemists also tried to find a law of nature on the basis of which it would be possible to systematize chemical elements. But they lacked reliable and detailed information about the elements. By the middle of the 19th century. knowledge about chemical elements became sufficient, and the number of elements increased so much that a natural need arose in science to classify them. The first attempts to classify elements into metals and non-metals turned out to be unsuccessful. The predecessors of D.I. Mendeleev (I.V. Debereiner, J.A. Newlands, L.Yu. Meyer) did a lot to prepare for the discovery of the periodic law, but were unable to comprehend the truth. Dmitry Ivanovich established a connection between the mass of elements and their properties.

Dmitry Ivanovich was born in Tobolsk. He was the seventeenth child in the family. After graduating from high school in his hometown, Dmitry Ivanovich entered the Main Pedagogical Institute in St. Petersburg, after which he went on a two-year scientific trip abroad with a gold medal. After returning, he was invited to St. Petersburg University. When Mendeleev began giving lectures on chemistry, he did not find anything that could be recommended to students as a teaching aid. And he decided to write new book– “Fundamentals of Chemistry.”

The discovery of the periodic law was preceded by 15 years of hard work. On March 1, 1869, Dmitry Ivanovich intended to leave St. Petersburg for the provinces on business.

The periodic law was discovered based on a characteristic of the atom - relative atomic mass .

Mendeleev arranged the chemical elements in increasing order of their atomic masses and noticed that the properties of the elements are repeated after a certain interval - a period, Dmitry Ivanovich arranged the periods one below the other., so that similar elements were located under each other - on the same vertical, this is how the structure was built periodic table elements.

March 1, 1869 Formulation of the periodic law by D.I. Mendeleev.

Properties simple substances, as well as the forms and properties of compounds of elements are periodically dependent on the atomic weights of the elements.

Unfortunately, at first there were very few supporters of the periodic law, even among Russian scientists. There are many opponents, especially in Germany and England.
The discovery of the periodic law is a brilliant example of scientific foresight: in 1870, Dmitry Ivanovich predicted the existence of three then unknown elements, which he named ekasilicon, ekaaluminum and ekaboron. He was able to correctly predict the most important properties of new elements. And then, 5 years later, in 1875, the French scientist P.E. Lecoq de Boisbaudran, who knew nothing about the work of Dmitry Ivanovich, discovered a new metal, calling it gallium. In a number of properties and the method of discovery, gallium coincided with eka-aluminum predicted by Mendeleev. But his weight turned out to be less than predicted. Despite this, Dmitry Ivanovich sent a letter to France, insisting on his prediction.
The scientific world was stunned that Mendeleev's prediction of the properties ekaaluminum turned out to be so accurate. From this moment on, the periodic law begins to take hold in chemistry.
In 1879, L. Nilsson discovered scandium in Sweden, which embodied what Dmitry Ivanovich predicted ekabor .
In 1886, K. Winkler discovered germanium in Germany, which turned out to be ecasilicium .

But the genius of Dmitry Ivanovich Mendeleev and his discoveries are not only these predictions!

In four places of the periodic table, D.I. Mendeleev arranged the elements not in the order of increasing atomic masses:

Back at the end of the 19th century, D.I. Mendeleev wrote that, apparently, the atom consists of other smaller particles. After his death in 1907, it was proven that the atom consists of elementary particles. The theory of atomic structure confirmed that Mendeleev was right; rearrangements of these elements not in accordance with the increase in atomic masses are completely justified.

Modern formulation of the periodic law.

The properties of chemical elements and their compounds are periodically dependent on the magnitude of the charge of the nuclei of their atoms, expressed in the periodic repeatability 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: “To the periodic law, the future does not threaten destruction, but only superstructure and development are promised.” How many chemical elements have been discovered in at the moment? And this is far from the limit.

A graphic representation of the periodic law is the periodic system of chemical elements. This is a brief summary of the entire chemistry of elements and their compounds.

Changes in properties in the periodic table with increasing atomic weights in the period (from left to right):

1. Metallic properties are reduced

2. Non-metallic properties increase

3. The properties of higher oxides and hydroxides change from basic through amphoteric to acidic.

4. The valence of elements in the formulas of higher oxides increases from ItoVII, and in the formulas of volatile hydrogen compounds decreases from IV toI.