3.13. Periodic Classification of Elements: Periodic Trends

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The Periodic Classification of Elements is one of the most important topics in Chemistry, and its understanding is crucial for a good performance in the Enem test. In this chapter, we'll cover periodic trends, which are patterns that can be observed among elements as we move up the periodic table.

The periodic table is organized into periods (horizontal lines) and groups (vertical columns). The properties of elements vary according to their position in the table, and these variations are called periodic trends. The most important periodic trends to consider are: atomic radius, ionization energy, electron affinity, and electronegativity.

Atomic Radius

Atomic radius is the distance from the nucleus of an atom to its outermost electron shell. In the periodic table, atomic radius increases from top to bottom in a group, because each period represents a new shell of electrons, making the atom larger. However, the atomic radius decreases from left to right in a period, because the number of protons in the nucleus increases, attracting electrons more strongly and therefore decreasing the atomic radius.

Ionization Energy

Ionization energy is the energy required to remove an electron from an atom. Ionization energy increases from left to right across a period because the number of protons in the nucleus increases, making it more difficult to remove an electron. Ionization energy decreases from top to bottom in a group because electrons are farther from the nucleus and therefore easier to remove.

Electronic Affinity

Electronic affinity is the energy released when an atom gains an electron. Electron affinity generally increases from left to right across a period because the number of protons in the nucleus increases, making the atom more likely to gain an electron. However, electron affinity doesn't change much from top to bottom in a group.

Electronegativity

Electronegativity is a measure of how strongly an atom attracts electrons in a chemical bond. Electronegativity increases from left to right across a period because the number of protons in the nucleus increases, making the atom more likely to attract electrons. Electronegativity decreases from top to bottom in a group because electrons are further away from the nucleus and therefore less likely to be attracted.

Understanding these periodic trends is crucial to understanding how elements interact with each other and form compounds. Furthermore, these trends can help predict the behavior of elements that have not yet been fully studied. Therefore, the Periodic Classification of Elements and their periodic trends are fundamental topics for the Enem test and for any in-depth study of Chemistry.

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423.14. Periodic Classification of Elements: Variation of properties along the table