Detailed Mechanism of Ionic vs. Covalent Chemical Bonding

Chemical bonds are the electromagnetic forces binding atoms together to form stable compounds:

• A.
• The Ionic Bond: Occurs strictly between a metal atom and a non-metal atom.
• Mechanistically: (1) The metal atom donates its valence electrons, becoming a positive cation; (2) The non-metal atom accepts these electrons, becoming a negative anion; (3) Enormous electrostatic attraction (Coulomb force) draws cations and anions into rigid, three-dimensional crystalline lattices.

• Classic Case: Sodium Chloride (NaCl).
• ₁₁Na (2,8,1) donates 1 electron to ₁₇Cl (2,8,7).
• Result: Na⁺ [2,8] and Cl⁻ [2,8,8] attract electrostatically to form crystalline NaCl table salt.
• Important property: Ionic bonds do not possess physical molecular shape (they form giant lattices) and cannot form between two metals or between two non-metals.

• B.
• The Covalent Bond: Occurs between two non-metal atoms of identical or similar electronegativities.
• Because neither atom can extract electrons completely, they mutually share electron pairs:

• (1) Single Covalent Bond: Each atom contributes 1 electron, sharing 1 electron pair (denoted by a single line —).
• Examples: Hydrogen gas H₂ (H—H), Chlorine gas Cl₂ (Cl—Cl), Water molecule H₂O (two single bonds H—O—H), and Methane CH₄.

(2) Double Covalent Bond: Each atom contributes 2 electrons, sharing 2 electron pairs (denoted by double lines =). Classic example: Oxygen gas O₂ (O=O), where each oxygen atom (2,6) needs 2 electrons to complete its octet.

• (3) Triple Covalent Bond: Each atom contributes 3 electrons, sharing 3 electron pairs (denoted by triple lines ≡).
• Classic example: Nitrogen gas N₂ (N≡N), where each nitrogen atom (2,5) shares 3 electrons, forming a tremendously strong triple bond that makes N₂ chemically inert at room temperature.