2.6. Atomic Structure: Electronic Layers

Atomic structure is one of the most important topics to be understood when studying Chemistry for ENEM. At the center of the entire study of Chemistry is the atom, the smallest unit of a chemical element that maintains the properties of that element. Therefore, understanding atomic structure is critical to mastering advanced chemical concepts.

The atom consists of three fundamental particles: protons, neutrons, and electrons. Protons and neutrons make up the nucleus of the atom, while electrons orbit the nucleus in different electron shells, also known as energy levels.

Each electron shell of an atom has a specific amount of energy associated with it. The first electron shell, which is closest to the nucleus, has the least amount of energy, while subsequent shells have increasing amounts of energy. Each shell can hold a specific number of electrons. The first shell can hold up to 2 electrons, the second shell can hold up to 8 electrons, and the third shell can hold up to 8 electrons.

Electrons in an atom tend to occupy the lowest energy shells first, before occupying the highest energy shells. This is known as the Aufbau principle. Therefore, if an atom has more than 2 electrons, the extra electrons occupy the second shell before occupying the third shell, and so on.

Furthermore, within an electron shell, electrons occupy different energy sublevels, which are designated by s, p, d, and f. Each subshell has a specific number of orbitals, and each orbital can hold up to 2 electrons. The s subshell has 1 orbital, the p subshell has 3 orbitals, the d subshell has 5 orbitals, and the f subshell has 7 orbitals.

The electrons in an atom also follow Pauli's principle, which states that each orbital can hold a maximum of 2 electrons and that these electrons must have opposite spins. This means that the electrons in a specific orbital must rotate in opposite directions.

The distribution of electrons in the electron shells of an atom determines the chemical properties of that atom. For example, atoms that have the same electron configuration in their outer electron shells (also known as valence shells) tend to have similar chemical properties. This is known as the octet rule, which states that atoms tend to gain, lose, or share electrons in order to have 8 electrons in their valence shell.

In summary, atomic structure and electron shells are fundamental concepts in Chemistry that are essential for understanding the properties and behavior of atoms. These concepts form the basis for more advanced topics in Chemistry, such as chemical bonds, chemical reactions, and the periodic table of elements.

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9Atomic Structure: Energy Sublevels

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