When it is said that having 8 valence electrons is the most "stable" configuration, it refers to the concept of the octet rule, which is a guideline in chemistry stating that atoms tend to gain, lose, or share electrons to achieve a stable electron configuration resembling that of the noble gases. Noble gases have full valence electron shells, typically with 8 electrons, except for helium, which has 2.
There are a few reasons why having 8 valence electrons is considered stable:
Energy minimization: Atoms strive to achieve a lower energy state. By having a full valence shell, an atom achieves a more stable configuration because it minimizes its overall energy. When atoms gain or lose electrons to reach an octet, they fill up or empty their outermost energy level, which often corresponds to a lower energy state.
Electron-electron repulsion: Valence electrons experience repulsion from each other due to their negative charges. By having 8 valence electrons, the electrons can arrange themselves more symmetrically, reducing electron-electron repulsion. This arrangement maximizes the overall stability of the atom.
Noble gas configuration: Noble gases, such as neon (Ne) or argon (Ar), have full valence electron shells. These gases are chemically inert and exhibit remarkable stability. Other elements tend to gain, lose, or share electrons to achieve a similar electron configuration as noble gases, including the octet configuration, which leads to increased stability.
It is important to note that the octet rule is a general guideline that applies to many elements and compounds, but there are exceptions and variations depending on the specific atoms and bonding patterns involved. Some atoms can achieve stability with fewer or more than 8 valence electrons, depending on their position in the periodic table and the types of bonds they form.