Every crystalline solid is a lattice, but what sits at the lattice points and what holds them together changes everything. Ions, metal ions, atoms or whole molecules: identify the particles and the properties follow.
A crystalline solid has a regular three-dimensional arrangement of particles called a lattice. There are four types: giant ionic (NaCl, MgO: ions held by ionic bonds), giant metallic (Cu: cations in delocalised electrons), giant molecular or covalent (diamond, graphite, graphene, SiO2: atoms joined by covalent bonds throughout) and simple molecular (I2, ice, C60: molecules held by weak intermolecular forces). To explain a property, name the particles, the force that must be overcome, and how strong it is.
Fig. 1: the four types of lattice
Section 01
The four lattices.
Rotate each lattice in the simulator: sodium chloride, copper, diamond and iodine. For each, ask what the particles are and what has to break to melt it.
Lattice
Particles
Melting point
Conducts?
Soluble in water?
giant ionic
ions
high
molten or aqueous only
often
giant metallic
cations + delocalised e−
usually high
yes, solid and liquid
no
giant molecular
atoms
very high
no (graphite, graphene yes)
no
simple molecular
molecules
low
no
polar ones may
Section 02
Carbon, four ways.
Switch to the carbon allotropes. The same element gives a hard insulator, a soft conductor, a one-atom-thick sheet and a molecule.
Diamond: each C bonded to four others tetrahedrally; very hard, very high melting point, no delocalised electrons so it does not conduct.
Graphite: layers of hexagons, each C bonded to three others; the fourth electron is delocalised, so it conducts along the layers. Weak forces between layers let them slide: soft and slippery.
Graphene: a single layer of graphite; very strong and an excellent conductor.
Buckminsterfullerene, C60: a simple molecule; weak id-id forces between molecules, so it sublimes at a much lower temperature and dissolves in some organic solvents.
Silicon(IV) oxide, SiO2: giant molecular like diamond, each Si bonded to four O and each O to two Si; melting point about 1700 °C.
Stage 1 · Learn
Check what the sim just showed you
Four quick checks. Each correct answer earns XP and records this skill on your profile.
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What type of lattice does diamond have?
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Why does graphite conduct electricity?
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Which solid has a simple molecular lattice?
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Why are alloys usually harder than the pure metals they contain?
Section 03
Ice, iodine and alloys.
Finish with the metals and alloys simulator: push a layer of pure metal, then add larger or smaller atoms and push again.
Iodine: I2 molecules in a regular lattice held by id-id forces; it sublimes gently on warming without breaking any I–I bonds.
Ice: each H2O hydrogen-bonded to four others in an open lattice, so ice is less dense than water.
Alloys: atoms of a different size disrupt the regular layers, so the layers cannot slide as easily. Alloys such as brass and steel are harder and stronger than the pure metals.
Examiner trap
For a giant molecular solid, melting breaks covalent bonds; for a simple molecular solid it overcomes only intermolecular forces. Mixing these up is the most common error in this section. Graphite conducts through delocalised electrons, not ions.
Stage 2 · Exam
Exam-style questions
Unlocks once the four checks above are done. Worth more XP, written to AS Paper 1 and Paper 2 standard.
Finish the four checks above to unlock the exam questions
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A substance melts at 1710 °C, does not conduct as a solid or liquid, and is insoluble in water. What is its structure?
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Buckminsterfullerene, C60, has a much lower sublimation temperature than diamond because:
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Why is graphite soft while diamond is very hard?
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Which substance conducts electricity both as a solid and when molten?
Skill unlocked
Lattice structures, mastered.
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