Chemical Knowledge Sharing – Periodic Law of Elements

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In 1867, the Russian chemist Mendeleev, based on his analysis of a large amount of experimental data, was convinced that \"finding the relationship between the properties of elements, their similarities, and their atomic weights is the simplest and most natural approach.\" When arranging elements in order of atomic weight, he avoided the mistakes made by his predecessors in a mechanical approach, and instead made systematic adjustments based on the systematic patterns in which the properties of elements change with atomic weight. A fairly complete periodic table of elements was obtained. In February 1869, he submitted a paper on the relationship between elemental properties and atomic weights, in which he outlined the principle that elements arranged in order of their atomic weights exhibit distinct periodicity in their properties, a principle he named the law of periodicity of elements. Guided by the periodic law (and the periodic table), 11 elements including gallium were predicted and discovered. The existence of noble gases was also predicted, and elements such as neon, krypton, and xenon were discovered one after another after 1898, leading to the addition of a new group to the periodic table. By 1944, all 92 elements in nature had been discovered. The periodic law of elements is the first scientific classification system for chemical elements. It profoundly reveals the inherent connections between elements, showing that they are not isolated but exist within a well-ordered natural sequence, with systematic classification and a complete framework. The periodic law connects the complex knowledge of elements and integrates it at a new theoretical level, thereby significantly advancing the development of chemistry. Based on the periodic law, it became possible not only to predict to some extent the properties of unknown elements and compounds, but also to discover the composition and structure of atoms, which guided research on atomic structure. It has had a profound impact on the study of material structure, the utilization of atomic energy, organic chemistry, metallurgy, geochemistry, as well as social sciences. The discovery of the periodic law of elements also has profound philosophical significance. The fact that the properties of elements undergo qualitative changes due to variations in atomic weight fully demonstrates the universality of the law that quantitative changes lead to qualitative changes. Therefore, Engels commented: “Mendeleev unconsciously applied Hegel’s law of the transformation of quantity into quality, thereby accomplishing a scientific feat.” ”As our understanding of the atomic structure improved, so too did our knowledge of the periodic law of elements. The electron arrangement in the atoms of chemical elements, and the properties of these elements that result from this arrangement (such as bonding ability and reactivity), are closely related to the atomic number (the charge of the atomic nucleus). The electron configuration changes in a regular, repetitive (periodic) manner as the atomic number increases from one element to the next. The periodicity of elements is essentially a reflection of the periodic changes in the internal structure of atomic nuclei; the periodicity of atomic structure is the underlying reason for the periodicity of elemental properties. According to the periodic law of elements, a table that arranges elements in order of atomic number is called the periodic table of elements, or simply the periodic table. It is a representation of the periodic system of elements; it was first proposed by Mendeleev, and later various forms of it were developed. The long-form periodic table proposed by the Swiss chemist Werner is widely used in modern times. In the long-form periodic table, there are 7 rows corresponding to 7 periods, which contain 2, 8, 8, 18, 18, 32, and 23 elements respectively (elements 93–109 are artificially synthesized radioactive transuranic elements). Period 1 is an extremely short period, Periods 2 and 3 are short periods, Periods 4 and 5 are long periods, Period 6 is an extremely long period, and Period 7 is an unfinished period. Each cycle begins with an element that has 1 electron in its outermost shell, and ends with an element that has 8 electrons in its outermost shell (with helium being an exception). The vertical columns in the periodic table are called groups; groups I–VII are divided into main groups (denoted by A) and transition groups (denoted by B). There are also group 0 (the noble gases) and group VIII (comprising 3 columns), for a total of 16 groups. The lanthanide and actinide elements, which belong to the inner transition elements, are placed in two separate rows at the bottom of the periodic table. Based on the atomic structure characteristics of elements, the periodic table can be divided into the s-block, p-block, d-block, ds-block, and f-block. In the modern long-form periodic table, Group 0 is sometimes referred to as Group VIIIA, while Group VIII is called Group VIIIB. Around 1966, theoretical researchers proposed the hypothesis that stable islands of superheavy elements might exist, showing people the broad prospects for an extended periodic table. To this day, some scholars believe that period 8 of the periodic table may consist of elements numbered 119 to 168, among which elements 121 to 153 are superactinides. Other scholars believe that period 8 of the periodic table may consist of elements numbered 119 to 164, among which elements 121 to 155 are superactinides. Period 9 may consist of elements numbered 165 to 172. Of course, theoretical predictions must also be tested through scientific experiments in order to determine their degree of accuracy.