IB Chemistry: Giant Covalent & Network Structures FAQ

A giant covalent structure is a lattice of atoms joined by a continuous network of strong covalent bonds, with no individual molecules involved — the whole crystal behaves as one enormous molecule. Melting means breaking every one of those bonds, which is why melting points run extremely high. Diamond and silicon dioxide are the classic IB examples.

The syllabus centres on four: diamond, graphite, silicon dioxide (SiO2), and — with more depth at HL — graphene and fullerenes as carbon allotropes. Each shares the same giant-lattice bonding but arranges atoms differently, which is exactly why graphite conducts electricity while diamond and silicon dioxide don't.

Diamond's four sp3 bonds per carbon lock every atom into a rigid 3D lattice, so melting means breaking millions of strong covalent bonds — hence its melting point near 3550°C. Graphite's carbons are sp2-hybridised and bonded to only three neighbours in flat sheets, leaving one delocalised electron per atom free to move and carry charge along the layer.

Yes — graphene appears under Structure 2.4, "from models to materials", where the current IB Chemistry guide (first exams 2025) treats it as a single-layer carbon allotrope whose delocalised electrons give very high electrical conductivity and tensile strength. HL students go deeper into fullerenes and nanotubes; SL students need the basic bonding picture only.

Most marks disappear because students describe diamond as having "strong bonds" without stating that every bond in the lattice must break for melting to occur, or they say graphite conducts because of "free electrons" instead of naming the delocalised electron each carbon contributes from its unhybridised p-orbital. Examiners mark the mechanism, not the adjective.

It's not conceptually difficult, but it's a high mark-loss topic because the vocabulary has to be exact — "covalent bond" versus "van der Waals force between layers" trips up more students than the actual chemistry does. In my experience marking mocks, weaker answers reach for "strong forces" as a catch-all where a named bond type was required.

All three form extended lattices with high melting points, but the bonding differs: giant covalent uses directional covalent bonds (diamond, SiO2), giant ionic uses non-directional electrostatic attraction between oppositely charged ions (NaCl, MgO), and giant metallic uses a "sea" of delocalised electrons around cations (Fe, Cu). Solid-state conductivity separates them cleanly on paper.

Start with the bonding type in each substance, then link structure to the property being asked about — never jump straight to the property. For "explain why diamond has a higher melting point than iodine," name diamond as giant covalent, where melting breaks strong covalent bonds, versus iodine's simple molecular structure, where only weak van der Waals forces between molecules break.

The most common command terms here are "describe", "explain", "compare" and "deduce" — each demanding a different depth. "Describe" wants the structure or bonding stated; "explain" wants the reasoning behind a property; "compare" needs both similarities and differences named explicitly, ideally in the same sentence.

Build a bonding-to-property chain for every substance you meet: identify the bond type, then the forces holding the whole structure together, then the property it explains. Students who jump straight from "covalent" to "high melting point" without naming what breaks lose the reasoning marks even when their final answer is technically correct.

Yes — the core content (diamond, graphite, silicon dioxide, and the bonding-to-property reasoning) is common to both levels. HL students get extra depth under Structure 2.4, covering carbon allotropes like fullerenes and nanotubes as engineered nanoscopic materials, with more emphasis on how structure links to real-world material properties.

Giant covalent bonding sits mainly in Structure 2.2, "the covalent model", where lattice bonding and properties are introduced, and reappears in Structure 2.4, "from models to materials", where diamond, graphite, silicon dioxide and carbon allotropes are treated as real materials with measurable properties. Both subtopics are examinable at SL and HL.

Nearly always it's precision, not understanding — your child likely knows diamond is hard and graphite conducts but isn't naming the exact bond broken or the delocalised-electron mechanism examiners are marking for. Structured practice against real mark schemes, not just re-reading notes, is what closes this gap fastest.