3.3. Periodic Classification of Elements: Organization of elements in the periodic table

The Periodic Classification of Chemical Elements is an essential tool for studies in chemistry. It is a graphical representation where the chemical elements are organized by their atomic number, electron configuration and related chemical properties. This organization makes the periodic table an invaluable resource for predicting the behavior of chemical elements, including those yet to be discovered.

The current periodic table, called the Long Periodic Table, was proposed by Glenn T. Seaborg in 1945 and made official by the International Union of Pure and Applied Chemistry (IUPAC) in 1957. It is divided into periods (horizontal lines) and groups ( vertical columns).

The periods represent the number of shells that the atoms of the elements have. In the periodic table there are 7 periods, which indicate the number of energy levels an atom has. Each period starts with an alkaline element (group 1) and ends with a noble gas (group 18).

The groups, in turn, are 18 and represent the number of electrons in the valence layer (last layer) of the atoms of the elements. Elements in the same group have similar chemical properties due to the same electron configuration in their valence shell.

The periodic table is divided into four blocks: s, p, d, and f, which correspond to the energy sublevel being filled with electrons. The s block contains groups 1 (alkali metals) and 2 (alkaline earth metals). The p block contains groups 13 through 18, which include representative metals, semimetals, nonmetals, and noble gases. The d-block contains groups 3 through 12, which are the transition metals. And the f-block is not included in the groups, but is composed of the lanthanides and actinides, known as internal transition elements.

Elements are also classified into metals, semimetals, and nonmetals. Metals are the majority of elements, are good conductors of heat and electricity, have a metallic luster, and are malleable and ductile. Non-metals have opposite properties, are poor conductors of heat and electricity, lack metallic luster and are brittle. Semi-metals or metalloids have intermediate properties between metals and non-metals.

In addition, the periodic table also presents the chemical series, which are sets of elements with similar properties. The main ones are: alkali metals (group 1), alkaline earth metals (group 2), chalcogens (group 16), halogens (group 17) and noble gases (group 18).

Understanding the organization of the periodic table and the properties of the elements is essential to solve chemistry questions in ENEM and other entrance exams. The periodic table is a powerful tool that allows you to predict the chemical behavior of elements, their reactions, compound formation, among other important aspects of chemistry.

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