CC1.4 — Chemical bonding (Edexcel 1SC0)

Ionic bonding

Formed between metals and non-metals. Metal loses electrons → positive ion (cation). Non-metal gains electrons → negative ion (anion). Electrostatic attraction between oppositely charged ions forms ionic lattice.

Properties: high melting/boiling points (strong ionic lattice); conduct electricity when molten or dissolved (ions free to move); often soluble in water.

Example: NaCl (Na⁺ and Cl⁻ in a giant ionic lattice).

Covalent bonding

Formed between non-metals. Atoms share pairs of electrons. Each shared pair = one covalent bond.

Simple molecules (e.g. H₂O, CH₄, CO₂): low melting/boiling points (weak intermolecular forces, not the covalent bonds themselves); do not conduct electricity.

Giant covalent structures (e.g. diamond, graphite, SiO₂): very high melting points (many strong covalent bonds); do not conduct electricity (except graphite — delocalised electrons).

Metallic bonding

Positive metal ions in a sea of delocalised electrons.

Properties: high melting points (strong metallic bonds); conduct electricity (delocalised electrons move freely); malleable/ductile (layers of ions can slide); lustrous.

Alloys

Mixture of metals (or metal + non-metal). Different-sized atoms disrupt regular layers → harder to slide → harder than pure metals. Examples: steel (iron + carbon), brass (copper + zinc), bronze (copper + tin).