Knowledge Organiser: Covalent Bonding
Key Terms
- Covalent bond: shared pair of electrons between non-metals
- Molecule: fixed group of atoms joined by covalent bonds
- Single bond: 1 shared pair (—)
- Double bond: 2 shared pairs (=)
- Triple bond: 3 shared pairs (≡)
- Lone pair: non-bonding electron pair
Must-Know Facts
- Covalent bonding: non-metals SHARE electrons
- H needs 1 bond, O needs 2, N needs 3, C needs 4
- H₂ (single), O₂ (double), N₂ (triple)
- Strong bonds within molecules; weak forces between
- No brackets on dot-cross diagrams (no ions formed)
- Triple bond strongest and shortest
Key Equations
- H₂O: O forms 2 bonds (2 shared pairs with 2 H atoms)
- CO₂: C forms 2 double bonds with 2 O atoms (C=O=C)
- NH₃: N forms 3 bonds with 3 H atoms (plus 1 lone pair)
- CH₄: C forms 4 single bonds with 4 H atoms
Common Mistakes
- Confusing covalent and ionic bonding: Covalent = sharing between non-metals; ionic = transfer between metal and non-metal
- Drawing brackets on covalent dot-cross diagrams: No brackets needed — covalent bonding forms no ions
- Saying covalent compounds have high melting points: Simple molecular covalent compounds have LOW melting points — weak intermolecular forces (not bonds) break easily
- Mixing up lone pairs and bonding pairs: Only the shared (bonding) pairs count as the covalent bond — lone pairs stay on one atom
Memory Aid
- Group 4 (C, Si) → 4 bonds (need 4 to reach 8)
- Group 5 (N, P) → 3 bonds (need 3 to reach 8)
- Group 6 (O, S) → 2 bonds (need 2 to reach 8)
- Group 7 (F, Cl) → 1 bond (need 1 to reach 8)
- Group 1 (H) → 1 bond (need 1 to reach 2)