The three types of chemical bond
Atoms react to achieve a full outer shell (the noble-gas configuration). They do this in three ways, giving the three types of chemical bond:
- Ionic bonding — between metals and non-metals.
- Covalent bonding — between non-metals.
- Metallic bonding — between metals (in pure metals and alloys).
Ionic bonding (metal + non-metal)
A metal transfers one or more electrons to a non-metal:
- The metal becomes a positive ion (cation).
- The non-metal becomes a negative ion (anion).
- Oppositely charged ions attract each other strongly — this is the ionic bond.
Example — sodium chloride:
- Na (2,8,1) → Na⁺ (2,8) + e⁻
- Cl (2,8,7) + e⁻ → Cl⁻ (2,8,8)
- Result: Na⁺ Cl⁻, a giant ionic lattice.
Covalent bonding (non-metal + non-metal)
Two non-metal atoms share one or more pairs of electrons. Each shared pair counts towards a full outer shell for both atoms.
Example — water (H₂O):
- Each H atom has 1 outer electron and needs 1 to fill shell 1.
- The O atom has 6 outer electrons and needs 2 to fill shell 2.
- Each H shares its electron with O; O shares one electron with each H. Two shared pairs.
Covalent bonds can be single (one pair, e.g. H₂, Cl₂), double (two pairs, e.g. O₂, CO₂) or triple (three pairs, e.g. N₂).
Covalent compounds form simple molecules (water, CO₂), giant covalent structures (diamond, graphite, silica) or polymers (poly(ethene)). Properties differ depending on structure (C2.6).
Metallic bonding (metal + metal)
In a metal, atoms are arranged in a regular structure called a giant metallic lattice. Each atom donates its outer-shell electrons to a "sea of delocalised electrons" that flows freely between the positive metal ions.
The strong attraction between the positive ions and the delocalised electrons is the metallic bond. This explains:
- Conduction (electrons move).
- Malleability (ions can slide past each other).
- High melting points (strong bonds).
Alloys (mixtures of metals) have different-sized atoms that disrupt the layers, making them harder than pure metals.
Decision flow — what type of bond?
If both atoms are non-metals → covalent. If one is metal, one non-metal → ionic. If both are metals (or single element) → metallic.
Drawing diagrams
- Dot-and-cross for ionic bonding: show electrons transferring; brackets and charges around each ion.
- Dot-and-cross for covalent bonding: show shared pairs in the overlap region; outer shells of both atoms shown together.
- Metallic: show positive metal ions in a regular pattern with "−" symbols representing delocalised electrons between them.
⚠Common mistakes
- Drawing transfer for non-metals. Two non-metals share, not transfer.
- Forgetting that metals donate ALL outer electrons to the sea — Na becomes Na⁺ with 0 outer-shell electrons.
- Saying ionic bonds are "between molecules". Ionic compounds form lattices, not molecules.
- Mixing ionic and covalent. Use the metal-metal/metal-nonmetal/nonmetal-nonmetal rule.
Links
Sets up C2.2 (ionic), C2.3 (covalent), C2.4 (metallic) and the property comparisons in C2.6.
AI-generated · claude-opus-4-7 · v3-deep-chemistry