O-Level Pure Chemistry: Chemical Bonding — Ionic vs Covalent vs Giant Structures

Ionic bonding

Transfer of electrons from metal to non‑metal → oppositely charged ions. Strong electrostatic attraction between positive and negative ions in a giant lattice. Explains: high melting / boiling point, conducts electricity only when molten / in aqueous solution (because ions are free to move).

Covalent bonding

Sharing of electron pairs between non‑metals. Simple covalent molecules (e.g. CO₂, H₂O) have low melting / boiling points because forces between molecules (weak intermolecular forces) are easy to overcome. They generally do NOT conduct electricity because there are no free mobile ions or electrons.

Giant covalent structures

Diamond: each C forms 4 strong covalent bonds → very hard, very high melting point, does not conduct electricity. Graphite: each C forms 3 bonds → layers with delocalised electrons → conducts electricity, soft/slippery (layers slide). These comparisons are favourite structured questions in Singapore O-Level Pure Chemistry.

Exam habits

• When asked “Why high melting point?”, say “strong electrostatic attraction / strong covalent bonds within a giant lattice that require large amount of energy to overcome”.
• Use the words “mobile ions / delocalised electrons” when explaining conduction.
• Do NOT just say “because it is ionic”. You must mention particles + forces.