The tendency of atoms to "want" or strive for eight electrons in their outermost shell is known as the octet rule. This rule is a general observation that applies to many elements, especially those in the main group elements of the periodic table.
The octet rule is based on the concept of achieving a stable electron configuration similar to that of noble gases. Noble gases, such as helium, neon, and argon, have completely filled outer electron shells and are chemically stable and unreactive. Other elements, by gaining, losing, or sharing electrons, can attain a similar stable electron configuration as noble gases, typically having eight electrons in their outermost shell. This configuration is known as an octet.
There are a few reasons why atoms tend to seek an octet in their outer shell:
Stability: Achieving an octet configuration provides a high degree of stability for atoms. It results in a full complement of electrons, which minimizes electron-electron repulsions and increases the overall stability of the atom.
Electrostatic attractions: The octet configuration allows atoms to achieve a more favorable balance of attractive and repulsive forces. With eight electrons, atoms can establish a more balanced distribution of positive and negative charges, leading to increased stability.
Ionic and covalent bonding: The octet rule guides the formation of chemical bonds. Atoms may gain or lose electrons to achieve an octet, forming ionic bonds, or they may share electrons through covalent bonds to reach the desired electron configuration.
It's important to note that while the octet rule is a useful guideline for understanding the stability of many elements, there are exceptions to this rule. For example, hydrogen and helium are exceptions as they can achieve stability with only two electrons in their outer shell. Additionally, elements in the d-block and f-block of the periodic table can have expanded valence shells due to the presence of d and f orbitals, respectively.