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AS · Practice questions · Lattice structures and properties

Structure decides properties.

Six original Cambridge-style questions on solid lattices: ionic, metallic, giant molecular and simple molecular structures and the properties that follow.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Particles, force, strength.

01
Recall
[4 marks]

Name the type of lattice in each of: (a) magnesium oxide, (b) copper, (c) graphite, (d) ice.

  • (a) giant ionic. ✓
  • (b) giant metallic. ✓
  • (c) giant molecular (covalent). ✓
  • (d) simple molecular (hydrogen-bonded). ✓
02
Explain
[3 marks]

Explain why silicon(IV) oxide has a much higher melting point than carbon dioxide, although both are oxides of Group 14 elements.

  • SiO2 is giant molecular: every Si is covalently bonded to four O throughout the structure. ✓
  • Melting it requires many strong covalent bonds to be broken. ✓
  • CO2 is simple molecular; melting or subliming it overcomes only weak id-id forces between molecules. ✓
03
Explain
[3 marks]

Explain why graphite conducts electricity and is used as a lubricant, but diamond does neither.

  • In graphite each C forms three covalent bonds; the fourth electron is delocalised and can move along the layers. ✓
  • The layers are held by weak forces, so they slide easily. ✓
  • In diamond each C forms four covalent bonds, leaving no delocalised electrons, and the rigid 3D network cannot slide. ✓
04
Explain
[2 marks]

Iodine is a shiny dark solid that turns to a purple vapour on gentle warming. Explain this in terms of its structure.

  • Solid iodine is a simple molecular lattice of I2 molecules held by id-id forces. ✓
  • These forces are weak, so little energy is needed to separate the molecules; the I–I bonds are not broken. ✓
05
Explain
[2 marks]

Explain why steel, an alloy of iron with carbon, is harder than pure iron.

  • The carbon atoms are a different size from the iron atoms and disrupt the regular layers. ✓
  • The layers can no longer slide over each other easily, so the alloy is harder. ✓
06
Analysis
[3 marks]

Substance X melts at 801 °C, does not conduct as a solid but conducts when molten, and dissolves in water. Substance Y melts at 114 °C and does not conduct in either state. Identify the type of lattice in each and justify your answers.

  • X is giant ionic: high melting point from strong ionic bonding; conducts only when molten because the ions become mobile; soluble in water. ✓
  • Y is simple molecular: low melting point because only weak intermolecular forces are overcome. ✓
  • Y contains no ions or delocalised electrons, so it never conducts (it could be iodine). ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.