The discovery of the periodic law of elements and the establishment and perfection of the periodic table of elements The periodic law of elements refers to the law that the properties of elements change periodically with the increase of atomic number. The periodic law of elements is one of the important basic theories in natural science, especially in chemistry. Its discovery is a great achievement of natural science, which has greatly promoted the development of chemistry and even the whole natural science. The establishment and development of the periodic law of elements and the periodic table of elements have made it what it is now, which is not smooth sailing, but has experienced fierce struggle between dialectics and metaphysics. Since 166 1, British chemist Boyle has published the book Suspicious Chemist. Since the concept of elements was put forward and chemistry was established as a science, metaphysics has occupied a dominant position in people's minds for a whole century and a half, and the actual information provided at that time was not sufficient. It was not until 1800 that 28 elements were discovered, and the dialectical relationship between elements could not be revealed. Chemists have to regard various chemical elements as independent and irrelevant, study them in isolation and separation, and engage in the simple accumulation of chemical elements. Later, with the development of production, science has also made great progress. The metaphysical view of nature has been opened one gap after another by a series of important discoveries in natural science, making it riddled with holes. The traditional concept that dozens of elements are isolated and unrelated to each other has also begun to arouse people's doubts. 18 15, prout put forward the hypothesis that "hydrogen atoms make up all elements", indicating that elements are not absolutely irrelevant. At that time, it was thought that the atomic weight of hydrogen was 1, which could not explain some atomic weights with decimals such as Cl (relative atomic mass is 35.5), so prout's view was not accepted by contemporary people. However, he thinks that the ideas related to elements are valuable and have a positive impact on future work. In the decades after prout, with the development of production practice, especially when people applied electricity to chemistry and discovered the method of electrolysis, people observed the spectra of various elements with spectral analysis instruments, and constantly discovered some new chemical elements, recognized their basic chemical properties, and revealed that there were more and more perceptual substances among elements. By 1869, 63 kinds of elements have been known and a lot of information about their physical and chemical properties has been accumulated. Therefore, people urgently need to sort out and summarize these perceptual materials. While looking for the internal relationship between the properties of elements, various elements classification theories are put forward. 1829, DEBAI Lai Na (3) divided 15 of the 54 elements at that time into five groups according to similarity, and put forward the "three-element group" hypothesis (4). People think that the three elements in a group not only have similar properties, but also have regular atomic weights. The atomic weight of the intermediate element is equal to the arithmetic average of the atomic weights of the two elements before and after. This is the first time to clearly put forward the relationship between atomic weight and element properties. 1826, the ancient capital made a spiral diagram on the cylinder. Arranging the elements on the helix in the order of increasing atomic weight, it is found that all the elements with similar properties are on the same vertical line. This is the first time to put forward the concept of cycle. 1864, German Meyer (5) published a list of six elements. In the table, he grouped six kinds and six kinds of elements with private properties in order of increasing relative atomic weight. But the six-element list did not include many elements, which was less than half of the known elements at that time. 1865, Englishman Newlands [6] arranged the known elements in order of relative atomic mass from small to large, and found that the eighth element was similar to the first element in nature, just like an octave syllable. He called this law "octave", but because he didn't fully estimate that there might be errors in the determination of relative atomic mass at that time, he mechanically followed the law of relative atomic mass from small to large. Therefore, the elements of his "octave" arrangement are confused in many places, which can not correctly reveal the internal relations between elements. By 1869, 63 kinds of chemical elements had been discovered, including 48 kinds of metals and 5 kinds of nonmetals 15, accounting for two thirds of the natural elements. On the basis of predecessors' work, Russian chemist Mendeleev has carefully studied the colors, boiling points, specific gravity, hardness, conductivity, magnetism, thermal conductivity and atomic weight of various elements. He wrote the names, atomic weights, oxides and various physical and chemical properties of 63 elements known at that time on the cards of each element. When sorting out these cards, he not only pays attention to the atomic weight of elements, but also attaches great importance to the properties of elements and their relationship with other elements. 1February, 869, Mendeleev arranged 63 elements into several rows in the order of increasing atomic weight, and aligned the elements with similar properties in each row left and right. When the position arranged in the order of atomic weight conflicts with the order of elements, he changes the position according to the properties of elements, or leaves a vacancy to make the properties of each horizontal row of chemical elements similar, and the changes of each vertical row of chemical elements also change periodically. 1869, the paper "Dependence of Element Properties on Atomic Weight" was put forward at the Russian Physical Chemistry Conference, and the periodic law of elements was discovered and the periodic table of elements was established. The paper includes the following contents: (1) If the elements are arranged according to the size of atomic weight, their properties show obvious periodicity. The size of atomic weight determines the characteristics of elements, just as the size of particles determines the properties of complex substances. Therefore, for example, similar compounds of S and Te, compounds of Cl and I, etc. , but also showed extremely obvious differences. ⑶ We should expect to find many unknown simple materials, such as Al-like and Si-like elements, with atomic weights between 65 and 67. (4) Knowing the atomic weight of a similar element of an element, we can sometimes correct the atomic weight of that element. Almost at the same time as Mendeleev, Meyer also proposed a similar periodic law of elements and arranged the elements in a table. It is pointed out that "the nature of elements is a function of atomic weight", and the atomic volume curve is drawn with the atomic weight of elements as the abscissa and the atomic volume as the ordinate. As a result, similar elements occupy similar positions on this curve, showing the functional relationship between atomic volume and atomic weight of each element. Although the periodic law of elements has been revealed by Mendeleev and published internationally, it has not been fully understood. Even the tutor Zining laughed at him for doing nothing. In people's indifference and ridicule, 187 1 year, Mendeleev improved and enriched the periodic table he formulated in 1869. Today, he published the article ⑼ Isoperiodic Dependence of Chemical Elements, which, like Meyer, divided the elements into eight groups, the main group and the sub-group. At the same time, he rearranged some elements (Os, Ir, Pt, Au; Te, me; Ni, CO), and revised the atomic weights of a series of elements (Sn, La, Ce, T, V, etc.). Finally, corresponding to the vacancy in the periodic table, Mendeleev predicted the existence and properties of new elements: aluminum-like, boron-like, silicon-like. Four years later, Abu Lang discovered gallium, which confirmed Mendeleev's prediction of aluminum-like. Four years later, Nelson discovered scandium and confirmed Mendeleev's prediction of boron-like. Seven years later, Winkler discovered germanium and confirmed Mendeleev's prediction of silicon-like. In the face of the fact that there is a lot of iron, the periodic law of elements is recognized. The success of Mendeleev's work caused a shock in the scientific community. In order to commemorate his achievements, people call the periodic law and periodic table of elements Mendeleev's periodic law and periodic table of elements. However, due to the limitation of the times, Mendeleev's law of internal relations of elements is not preliminary, and he failed to recognize the basic reasons for the periodic changes of element properties. However, it should be pointed out that Mendeleev's periodic law of elements and the periodic table of elements based on it are not perfect and there are still many problems. For example, is there an element between H and Li? Why should tellurium (128) and iodine (127) be reversed? How many rare earth elements are there? How should their positions be arranged in the table? What is the reason why the properties of elements are periodic with the increase of atomic weight? Wait a minute. When these problems have not been solved, the periodic law has encountered a severe test. Remsay discovered the inert gas argon in 1894. The atomic weight of argon is 39.9. It should be between potassium (39. 1) and calcium (40. 1), but there is no room left here. This new discovery contradicts what has been established. At that time, some people still advocated putting argon before potassium, and even some people doubted the correctness of the facts in the face of this new contradiction, thinking that argon and helium discovered later were not chemical elements, but gas mixtures, in an attempt to solve the contradiction between argon and potassium in atomic weight. 1895, Remsey discovered another inert gas helium on the earth. Because the properties of argon and helium are very similar and very different from those of other elements found in the periodic table, people assume that helium and argon may be another group of elements, which adds a new "O" family to the periodic table. The new vacancy promotes the development of other inert gas elements. Remsay discovered krypton, neon and xenon in 1898, and Donna discovered radon in 1900. These new scientific achievements gradually improved the periodic law. Another development of the periodic law is that after Rutherford put forward nuclear models in 19 1, Moseler used the experimental method of X-ray to determine the number of positive charges-atomic number in 19 13, and discovered the law of atomic number. It is pointed out that the real basis of periodic law is not atomic weight, but the nuclear charge number of element atoms. This is an important development of the periodic law, which relates the periodicity of the change of element properties to the nuclear charge number of element atoms. Some contradictions that are not arranged according to atomic weight are solved, such as cobalt (39. 1) and nickel (58.7), tellurium (127.3) and iodine (126.9), argon (39.9) and potassium (39./kloc-). It also solves the problem that there can be no other elements between hydrogen and helium. The inconsistency between atomic weight and atomic number was later solved by the discovery of isotopes. The third development of periodic law is that Bohr quoted quantum theory in 19 13, and concluded that the distribution of electrons in atoms has a layered structure. 19 16 sommerfeld put forward the theory of orbital stratification and quoted the concept of quantitative orientation of orbits in electromagnetic fields. 1925, Pauli put forward the incompatibility principle that two electrons cannot be in the same quantum state, stipulated the maximum number of electrons in each layer, and established that the state of each electron in an atom is described by four quantum numbers, but there cannot be two electrons with the same four quantum numbers in the same atom. The development of quantum mechanics further clarifies the layered structure of electrons in atoms. This reveals that the properties of elements change periodically because the electronic shell structure of atoms changes periodically. Generally speaking, when we talk about the periodic law, we always point out the periodicity of the change of element properties according to the periodic direction. But as early as 1887, Bazarov pointed out that in the family of the periodic table of elements, the atomic weights of elements are periodically changing. 19 15 years, in a series of works such as the second periodic phenomenon, billion studied the periodic changes of some properties of elements in the same periodic table. It has deepened our understanding of the periodic table of elements and the periodic law. In recent decades, a large number of super-axis elements have gained fame, and the periodic table of elements has gained fresh content. In a word, since the birth of 1869, the periodic law and the periodic table of elements have never been fixed or complete, but have been constantly revised, enriched and developed with the deepening of practice, and there is a process of gradual improvement. Even today's periodic table (⑿) is not perfect, and it is impossible to stay at the same level forever. With the progress of society and science and technology, the periodic law of elements will be more perfect and enriched. References:

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