Elements that have 8 electrons in their outermost shell are referred to as having a stable octet or achieving an octet configuration. This is also known as the octet rule.
The octet rule states that atoms tend to gain, lose, or share electrons in order to achieve a stable electron configuration with 8 electrons in their outermost shell (except for hydrogen and helium, which are exceptions to the rule). This is because having 8 electrons in the outer shell, known as the valence shell, corresponds to achieving a configuration similar to the noble gases, which are highly stable due to their full outer shells.
By achieving an octet configuration, elements can attain a more stable and lower energy state. There are a few different ways elements can achieve an octet:
Ionic Bonding: Elements can either gain or lose electrons to achieve an octet. For example, metals tend to lose electrons and form positively charged ions (cations), while nonmetals tend to gain electrons and form negatively charged ions (anions). The resulting attraction between oppositely charged ions forms an ionic bond.
Covalent Bonding: Elements can share electrons with other atoms to achieve an octet. In covalent bonding, atoms form molecules by sharing pairs of electrons between them. This allows both atoms to achieve a stable octet by sharing electrons in their overlapping orbitals.
Multiple Bonds: In some cases, elements may form multiple bonds to achieve an octet. For example, oxygen (O) forms a double bond (sharing two pairs of electrons) with another oxygen atom in O2, achieving a total of 8 electrons in its outer shell.
The octet rule helps explain the chemical behavior of many elements and is a guiding principle in understanding chemical bonding and molecular structure. However, it is important to note that the octet rule is a simplified model and does not apply to all elements or compounds, especially those beyond the second period of the periodic table or those with expanded valence shells.