2.11. Atomic Structure: Atomic Radius

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The atomic structure is one of the fundamental concepts of chemistry, being crucial for the understanding of many other topics in the discipline. In this chapter, we'll explore one of the most important aspects of atomic structure: the atomic radius.

The atom is the basic unit of matter, composed of three types of subatomic particles: protons, neutrons and electrons. Protons and neutrons are located in the nucleus of the atom, while electrons orbit around the nucleus in regions of space known as orbitals.

The atomic radius is a measure of the size of the atom, more specifically the distance from the center of the nucleus to the edge of the electron cloud. However, it is important to note that electrons do not have a precise location, but rather a probability of being found in certain regions around the nucleus. Thus, the atomic radius is an approximate measure and varies depending on the energy state of the atom and the type of chemical bond in which it is involved.

There are several ways to determine the atomic radius. One is through the X-ray method, which involves the diffraction of X-rays by a crystal of the element in question. Another way is through spectroscopy, which involves analyzing the light emitted or absorbed by an atom.

Atomic radii vary considerably among different elements. In general, atomic radius increases as you move down a group in the periodic table, due to the increase in the number of electron shells. However, atomic radius generally decreases as you move from left to right across a period of the periodic table, due to the increase in effective nuclear charge that draws electrons closer to the nucleus.

In addition, the atomic radius can also be affected by other factors, such as the charge of the ion. Cations, which are positively charged ions, usually have a smaller radius than their corresponding neutral atoms, because the loss of electrons results in a greater attraction of the nucleus for the remaining electrons. On the other hand, anions, which are negatively charged ions, usually have a larger radius than their corresponding neutral atoms, because the gain of electrons results in a greater repulsion between the electrons.

Understanding atomic radius and the factors that affect it is crucial to understanding many chemical concepts and phenomena, including the formation of chemical bonds, the properties of elements and compounds, and chemical reactions.

In summary, the atomic radius is a measure of the size of the atom and is influenced by several factors, including the position of the element in the periodic table and the charge of the ion. Understanding the atomic radius is fundamental to understanding chemistry and is a topic that will certainly appear on the ENEM exam. Therefore, it is important to study and understand this topic thoroughly.

In the next chapter, we'll explore another important aspect of atomic structure: ionization energy. Stay tuned and keep studying!

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142.12. Atomic Structure: Ionization Energy