3.5. Periodic Classification of Elements: Periodic Properties

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The Periodic Classification of Elements, also known as the Periodic Table, is an essential tool for the study of Chemistry. It organizes all known chemical elements according to their properties and atomic structures, allowing scientists to predict the behavior of an element and its possible chemical combinations. For the student preparing for the Enem, understanding this classification is essential, as questions about the periodic properties of elements are frequently addressed in the test.

Elements in the Periodic Table are arranged in horizontal rows called periods and vertical columns called groups. Elements in the same group share similar chemical properties. For example, Group 1 (excluding Hydrogen) is known as the alkali metals and includes elements such as Lithium, Sodium and Potassium, which are highly reactive.

Periodic properties are characteristics that repeat in a regular and predictable way as we move along the Periodic Table. They are mainly determined by the electronic structure of the atoms of the elements. The main periodic properties are: atomic radius, ionization energy, electron affinity and electronegativity.

The atomic radius is the distance from the nucleus to the outermost shell of the atom. As we move from left to right across a period, the atomic radius generally decreases. This is because the added electrons are in the same energy shell, but the number of protons in the nucleus increases, more strongly attracting electrons to the nucleus. As we go down a group, the atomic radius increases, as electrons are being added to new energy shells, farther from the nucleus.

The ionization energy is the energy required to remove an electron from an atom in the gaseous state. It increases from left to right across a period as the atomic radius decreases, making it more difficult to remove electrons. Ionization energy decreases as we go down a group because the atomic radius increases, making it easier to remove electrons.

The electronic affinity is the energy released when an atom in the gaseous state gains an electron. It increases from left to right across a period as the atomic radius decreases, making the atom more likely to gain electrons. Electron affinity generally decreases down a group as the atomic radius increases, making the atom less likely to gain electrons.

The electronegativity is the measure of an atom's ability to attract electrons in a chemical bond. It increases from left to right in a period as the atomic radius decreases. Electronegativity generally decreases as we go down a group as the atomic radius increases.

In summary, the study of the Periodic Classification of Elements and periodic properties is fundamental to the understanding of Chemistry. This knowledge will allow the student to predict the behavior of elements and their combinations, which is essential for solving complex chemical problems. Therefore, dedicate yourself to this topic to ensure a good performance in the Enem Chemistry test.

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343.6. Periodic Classification of Elements: Electronegativity