Chemical Bonding Explained: Ionic vs Covalent Bonds with Dot-and-Cross Diagrams

Atoms of noble gases (Group 18) possess exceptionally stable electron configurations containing 8 electrons in their valence shell (or 2 for Helium). The Octet Rule states that atoms tend to gain, lose, or share electrons to attain this inert noble gas configuration, leading to the formation of chemical bonds.

An ionic bond is formed by the complete electrostatic transfer of one or more electrons from a metallic electropositive atom to a non-metallic electronegative atom:

• Example (Sodium Chloride, NaCl): Sodium (2,8,1) loses 1 electron to form Na⁺. Chlorine (2,8,7) gains 1 electron to form Cl^–. The resulting electrostatic attraction creates a solid ionic crystal lattice.
• Characteristics: High melting and boiling points, soluble in water, and conducts electricity in molten or aqueous state.

When two non-metals combine, their electronegativity difference is insufficient for electron transfer. Instead, they share electron pairs:

• Single Covalent Bond: One shared pair of electrons, e.g., H₂ or Cl₂.
• Double Covalent Bond: Two shared pairs of electrons, e.g., O₂ (O=O).
• Triple Covalent Bond: Three shared pairs of electrons, e.g., N₂ (N≡N).

Covalent compounds generally have lower melting points and do not conduct electricity in pure liquid state.