Electron Shells

Electrons revolve around an atom’s nucleus at specific distances. Electrons closer to the nucleus have lower energy compared to those in more distant orbits. The energy of electrons in an atomic structure is quantized, meaning only distinct energy values are allowed for these orbits.

Electron Shells
Electron Shells

Energy Levels

Each orbit corresponds to a specific energy level and is grouped into energy bands known as shells. Atoms have a fixed number of shells, each with a maximum number of electrons allowed. Shells are numbered 1, 2, 3, etc., with 1 being the closest to the nucleus. The figure illustrates this concept with two energy levels. Different elements may have additional shells. The number of electrons in each shell follows the pattern 2N², where N is the shell number. For example, the first shell (N = 1) can have up to two electrons, the second shell (N = 2) up to eight electrons, and so forth.

Valence Electrons

Electrons in outer orbits have higher energy and are less tightly bound to the atom due to decreasing attraction from the nucleus. Electrons in the outermost shell, known as the valence shell, are called valence electrons. These electrons play a crucial role in chemical reactions, bonding, and determining the electrical properties of materials.

Free Electrons and Ions

If an electron absorbs enough energy, it can escape the atom and become a free electron. When an atom or group of atoms has a net charge, it is referred to as an ion. For instance, if a hydrogen atom loses an electron, it becomes a positive ion (H⁺). Conversely, if it gains an electron, it becomes a negative ion (H⁻). The behavior of electrons in different energy levels and their interactions contribute to the overall properties and behavior of atoms and materials.


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