PERIODIC TABLE of D. I. Mendeleyev — the natural classification of chemical elements representing the fullest and comprehensive graphic expression of the periodic law opened by D. I. Mendeleyev. Item of page x. aa. reflects objectively existing interrelation between chemical elements therefore she also was called D. I. Mendeleyev natural system.
The periodic law of D. I. Mendeleyev and P. based on it of page x. aa. are of exclusively great importance for science and practice. They were a basis for opening of new chemical elements, exact determination of their combining weights (masses), development of the doctrine about a structure of atoms, establishments of geochemical laws of distribution of elements in crust and development of modern ideas of living material which structure and the related patterns are according to the periodic law. Biol, activity of elements and their contents in an organism correspond to the place, a cut they occupy page in P. x. aa. So, with increase in sequence number in a number of groups toxicity of elements increases and their contents in an organism decreases. The periodic law is bright expression of the most general dialectic laws of development of the nature. Having arisen in a subsoil of chemistry, the periodic law became the general law of modern natural sciences. Item of page x. aa. systematized a huge number of the facts separated earlier relating to chemistry and physics of elements and their connections.
Attempts of classification of chemical elements by their combining weights (masses) were made also to D. I. Mendeleyev, they are available in works of Shankurtua (A. Chancour-tois, 1862), Meyer (L. Meyer, 1864) and Nyyulendsa (J. Newlands, 1866). However any of D. I. Mendeleyev's predecessors could not realize and formulate the periodic law reflecting an interconnection between chemical elvkhment and on the basis of this law to predict existence of new, yet not known elements.
On March 1, 1869 D. I. Mendeleyev published the table «Experience of the System of Elements Based on Their Atomic Weight and Chemical Similarity». This date is considered the opening day of the periodic law and P.'s creation by the village x. aa. Over P.'s improvement by the village x. aa. D. I. Mendeleyev worked until the end of the life (1907). All chemical elements (63) known by then it arranged in ascending order of them combining weights (see) also established that in this row through certain intervals the elements similar on the chemical properties meet. On this basis D. I. Mendeleyev formulated the periodic law as follows: properties of simple bodies, and also forms and properties of connections of elements are in periodic dependence on size at. scales of elements.
Value of any true law of nature consists not only in association and an explanation of already known facts, but also in anticipation and opening of new, earlier unknown phenomena and patterns. During development of the first options P. of page x. aa. D. I. Mendeleyev found out that combining weights of 17 of 63 the elements, known in his time, are determined incorrectly and shall be corrected. More exact determination of combining weights of these elements showed that D. I. Mendeleyev was right. Using the periodic law, D. I. Mendeleyev predicted existence of a number of unknown at that time of elements, in detail specifying what properties they shall have. Afterwards all these elements were found in the nature or received artificially. Properties of three of them — the scandium, gallium and germanium discovered during lifetime of D. I. Mendeleyev almost completely matched predicted. It promoted universal acceptance of the periodic law and its statement in science.
Developing and improving a tabular form P. of page x. aa., in which elements were placed in ascending order of their combining weights (masses) (according to the initial formulation of the periodic law), D. I. Mendeleyev found out that three couples of elements shall be located in the table as it should be, the return to their combining weights (masses). Argon and potassium, cobalt and nickel, tellurium and iodine were these elements. Therefore, the main characteristic defining properties of an element is not the atomic weight (weight), but the place taken by an element in a periodic system i.e. its sequence (atomic) number in this system. Thus the formulation of the law of D. I. Mendeleyev took the following form: properties of elements are in periodic dependence on the size of their sequence (atomic) numbers. The condition of physics and chemistry at the end of 19” — the beginning of 20 centuries did not give the chance to open inner meaning of the concept «sequence number». It became available after D. I. Mendeleyev's death.
In the first quarter of 20 century the facts testimonial of complexity of an atomic structure were received (see. Atom ). On the basis of the nuclear theory of an atomic structure offered in 1911 by E. Rutherford, and these X-ray spectrums of elements it was established that sequence number of an element in P. of page x. aa. it is equal to number of positive charges of an atomic nucleus of this element and since atom in general electro-is neutral — that and to number of the electrons surrounding its kernel. In the light of these data the periodic law is formulated as follows: properties of elements, and also forms and properties of their connections are in periodic dependence on the size of positive electric charge of kernels of their atoms. It means that in a continuous number of the elements located in ascending order of the size of electric charge of kernels of their atoms, elements with similar properties will periodically repeat.
By the end of the 70th of 20 century more than 400 versions of the graphic representation of P. of page were created x. aa. From them two options are most widespread, both were for the first time offered D. I. Mendeleyev: a so-called long form of the table in which the periods were located in one line, and more compact, short form presented in this article.
In the table seven periods are located across (are designated by the Roman figures). From them I, II and III, consisting of elements of the same kind, are called small, and IV, V, VI and VII — the big periods. Each big period (except for VII) includes two horizontal rows — even (upper) and odd (lower).
In the I period there are two elements, in II and III — 8, in IV and V — 18, in VI — 32 and in VII, incomplete — 21.
Every period except for I begins an element with pronounced metallicity (alkali metal) and comes to an end with inert gas. Elements II and III of the periods D. I. Mendeleyev called typical, their properties naturally and sharply change from typical metal to inert gas.
In odd ranks of the big periods of property of elements among change the same as properties of typical elements. In even ranks of the big periods there are elements only with metallicity.
In an even number VI of the period after lanthanum 14 elements with sequence numbers 58 — 71 which received the name follow lanthanides (see); they are similar on the properties to lanthanum. In the VII period of 14 elements following actinium with sequence numbers 90 — 103 make family actinoids (see). They are also allocated separately and located, as well as lanthanides, in the bottom of the table.
By 70th 20 century all gaps in P. of page x. aa. were filled so that sequence numbers of elements formed a continuous row. D. I. Mendeleyev considered the VII period unfinished and allowed a possibility of expansion P. of page x. aa. towards heavy elements behind uranium. This his anticipation was true: The VII period was replenished with the new, artificially received, so-called transuranic elements with sequence numbers 93 — 106. Most of them is received an amer. the chemist of G. Th. Seaborg who called the 101st element mendelevium in honor of the creator of the periodic law and in acknowledgement of the leading role of this law in opening and a prediction of properties of new chemical elements.
In vertical rows of P. of page x. aa. eight groups are located. Number of group is equal to the highest oxidation level (to valency on oxygen) the elements which are in group. Exception make fluorine (its oxidation level is equal — 1), copper, silver, gold (oxidation level - f l, +2 and +3). From elements VIII of group +8 only osmium and ruthenium have oxidation level. Each group shares on a dya of subgroup — main (in the table it is located more to the right) and collateral. The main subgroup includes typical elements and similar to them on properties elements of the big periods.
Secondary subgroups make only metal elements of the big periods. On chemical properties elements of each subgroup of one group considerably differ from each other, and only the highest oxidation level is identical to all elements of this group. Thus, subgroups combine elements of this group most similar among themselves.
For all elements, except helium, neon and argon, connections with oxygen are known. In II. page x. aa. the general formulas of the highest oxides formed by elements of each group are located under each group in ascending order of oxidation level. In formulas R means an element of this group.
Elements of the main subgroups, starting with the IV group, with hydrogen form gaseous connections. The general formulas of hydrogen bonding are located under each group and belong only to elements of the main subgroups.
At elements of the main subgroups in the direction from top to down table strengthening of metallicity and easing nonmetallic is noted (so, francium is an element with the most pronounced metallicity, and fluorine — nonmetallic). Thus, the place of an element in P. of page x. aa. (sequence number) determines the sum of its properties, to-rye represent an average from properties of the next elements on a vertical and a horizontal. Nek-ry groups of elements carry special names. So, elements of the main subgroups of the I group are called alkali metals (see), the II groups — alkaline earth metals (see), the VII groups — halogens (see), the elements located behind uranium — transuranic (see. Actinoids ).
Elements, to-rye are a part of live organisms and take part in processes of a metabolism, call biogenic elements. All of them occupy an upper part of the table of D. I. Mendeleyev. It is O, C, H, N, Ca, P, K, S, Na, Cl, Mg and Fe making the ground mass of living material (more than 99%). Six of them: H, O, N, C, P, S often call organogens. These are those elements which atoms have the smallest sizes and are capable to form multiple bonds. The most important biopolymers are constructed of them: proteins (see), nucleic acids (see), polysaccharides (cm). Biogenic elements which maintenance in live organisms is not enough are called microelements (see).
The reason of frequency of change of properties of chemical elements and order of their arrangement in D. I. Mendeleyev's table was explained on the basis of the theory of an atomic structure. The space around an atomic nucleus is filled with electrons which number is equal to the size of positive charge of an atomic nucleus, i.e. sequence number of an element. Being located at various distances from a kernel, electrons form electron shells (layers), or the energy levels designated, beginning from a kernel, numbers 1, 2, 3, 4, 5, 6, 7 or letters K, L, M, N, P, Q respectively. The integer tg, designating number of energy level, is called the main quantum number. It defines energy of the electrons occupying this electronic level. The smallest energy electrons of the first energy level, the closest to an atomic nucleus have. In process of increase in number p energy of electrons increases, and durability of their communication with a kernel decreases. The number of energy levels, or electron shells, is equal in atom of this element to number of the period, in Krom there is an element. The maximum number of electrons at this energy level to N equally doubled square of the main quantum number:
N = 2n 2
Thus, on first, the energy level, next to a kernel, there can be no more than two electrons, on the second — no more than 8, on the third — no more than 18, on the fourth — no more than 32.
Each electron shell is subdivided into subshells (subtotals) to note non-equivalence of the electrons of the same cover several differing from each other in binding energy with an atomic nucleus. Each subshell is characterized by the certain size Z called by the orbital (collateral) quantum number accepting numerical values from 0 to p — 1. The number of subshells is equal to value of the main quantum number: the first cover has one subshell, the second — two, the third — three, the fourth — four. It is accepted to designate electronic subshells Latin
letters 5 (I = 0), p (I = 1), d f/= 2), / (I = 3).
Subshells, in turn, consist of orbitals. An orbital call space around an atomic nucleus, in Krom finding of an electron is the most probable. The subshell of each cover, next to an atomic nucleus, consists from one 5 orbitals; second (r-subshell) consists of three r-orbitals; third (d-podobo-lochka) contains five d-orbitals; the fourth (/-a subshell) consists of seven / - orbitals. On each orbital there can be either one, or two electrons with opposite directed spins (the so-called principle of Paulie). Spin (English spin spinning, spinning) simply can be presented as rotation of an electron around own axis clockwise or counterclockwise. The maximum number of electrons, a cut each cover contains, it is equal 2(2Z + 1): the s-subshell contains 2(2 * About + 1) = 2 electrons; r-podobo-lochka — 2(2 • 1 + 1) = 6 electrons; a d-subshell — 2(2 • 2 + 1) = 10 electrons; / - a subshell — 2(2 • 3 + + 1) = 14 electrons. Proceeding from it, find simple addition number of electrons in consecutive covers. Filling of electron shells and subshells happens according to the principle of a minimum of energy: with increase of number of electrons each following electron holds position with the smallest energy, and then — with the increasing energy. For atoms of many elements this order corresponds to the fact that at first covers with a smaller tg, and then covers with big tg are filled. Within one cover at first subshells with I = 0, and then subshells with big sizes I are filled, up to I = tg — 1. However in mnogoelekt-ronny atoms as a result of interaction of electrons at the size of the main quantum number, equal 3 (M-cover), equal 4 (iV-about-lochka) etc., states with big sizes p and small sizes I have smaller energy and states with smaller sizes tg, but with big sizes I are energetically more favorable, than. In D. I. Mendeleyev's table it is shown how subshells of each element are filled. Disturbances of ideal filling of subshells begin with potassium (sequence number 19). The nineteenth electron of potassium would have to occupy a d-subshell in the M-cover, but chemical and optical properties of potassium are similar to similar properties of lithium and sodium which the valence electron occupies respectively 5 subshell in a L-cover and 5 subshell in the M-cover. Therefore and at potassium the nineteenth electron shall be in s-podobo-lochke iV-cover. From potassium (sequence number 19) to scandium (sequence number 21) at the blank d-subshell in the LG-cover «building» of iV-oboloch-ki begins. Since scandium, filling of d-podoboloch-ki of the M-cover is resumed, a cut comes to an end at copper (sequence number 29). Further to krypton (sequence number 36) there is a normal filling of a ^-cover.......... Such energetically favorable filling элект^-ронных covers ledges happens also at other elements. Depending on what subshell is filled with electrons of the last, all elements are subdivided into four types: 5 elements (the last fills 5 subshell of an external cover), belong to 5 elements the first two elements of every period; p-elements (electrons fill a r-subshell of an external cover), belong to p-elements the last six elements of every period, except elements I and VII of the periods; d-elements (to the last it is filled with electrons of d-podobo-lochka second outside of a cover, and on an external subshell there are one or two electrons, at palladium — any); transition elements of the big periods located between s-and p-elements concern to them; and, at last, / - elements (electrons fill a subshell of the third, considering outside, covers, and on an external subshell remain two electrons), to / - to elements belong lanthanides and actinoids.
Thus, frequency of properties of elements has a talk repeatability of number of external electrons with increase in sequence number of an element. Chemical properties of elements therefore electrons, to-rye can participate in formation of chemical (valent) bonds are defined by number of external electrons, call valent (see. Valency ).
Bibliography: Vinogradov A. P. Chemical elementary composition of organisms and periodic system of D. I. Mendeleyev, Works Biogeochemical, Academy of Sciences of the USSR laboratories, t. 3, page 5, JI. — M, 1935; The Horizons of biochemistry, the lane with English, under the editorship of JT. A. Tumer-mana, page 102, M., 1964; Mendeleyev D. I. Periodic law, M., 1958; <Periodicheskiyzakon D. I. Mendeleyeva and its philosophical value, M., 1947; Shchukarevs. A. Inorganic chemistry, t. 2, page 350, M., 1974.
V. P. Mishin.