Chemical Bonding and Molecular Structure - Kossel-Lewis Approach to Chemical Bonding

Kossel and Lewis developed the electronic theory of valence to explain why atoms combine. They postualted that atoms achieve stability by attaining the nearest noble gas configuration ($ns^2 np^6$).

Lewis Symbols: These are notations where valence electrons are represented as dots surrounding the chemical symbol of the element (e.g., $\cdot Li$, $: \dot{B} \cdot$).

Octet Rule: Atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons, achieving a stable octet (except Hydrogen, which follows the duplet rule).

Ionic (Electrovalent) Bond: Formed by the complete transfer of one or more electrons from one atom to another, resulting in electrostatic attraction between the formed cations and anions.

Covalent Bond: Formed by the sharing of at least one pair of electrons between two atoms to satisfy the octet rule for both.

Formal Charge: The difference between the number of valence electrons in an isolated atom and the number of electrons assigned to that atom in a Lewis structure.

Limitations of the Octet Rule: It does not account for the 'Incomplete Octet' (e.g., $LiCl$, $BeH_2$, $BCl_3$), 'Odd-electron molecules' (e.g., $NO$, $NO_2$), or the 'Expanded Octet' (e.g., $PF_5$, $SF_6$, $H_2SO_4$).