CCEA GCSE Chemistry 1.3 Structures Exam Questions

About CCEA GCSE Chemistry 1.3 Structures

Structures is a Unit 1 topic in CCEA GCSE Chemistry that links the type of bonding to the physical properties of substances. You need to describe and explain the melting points, electrical conductivity and solubility of giant ionic lattices, simple molecular covalent substances, giant covalent substances (diamond, graphite and graphene) and metals. The topic also covers why alloys are harder than pure metals and how to classify an unknown substance from data about its properties. It builds on 1.2 Bonding and leads into nanoparticles. Examiners often ask for explanations of melting point or conductivity that mention the correct particles and forces, and comparisons of diamond and graphite.

What you need to know

• Giant ionic A regular lattice of oppositely charged ions held by strong electrostatic forces in all directions. High melting points because a lot of energy is needed to overcome these forces. They conduct electricity only when molten or in solution, because ions are then free to move.
• Molecular covalent Small molecules with strong covalent bonds inside but weak forces of attraction between molecules. Low melting and boiling points because only the weak intermolecular forces are overcome. They do not conduct because there are no charged particles free to move.
• Diamond Each carbon atom forms four covalent bonds in a giant tetrahedral structure. Very hard with a very high melting point; does not conduct as there are no delocalised electrons. Used in cutting tools.
• Graphite and graphene In graphite each carbon forms three covalent bonds in hexagonal layers with weak forces between layers, so layers slide (soft, used as a lubricant and in pencils). One electron per carbon is delocalised, so graphite conducts. Graphene is a single layer of graphite: very strong, light and a good conductor.
• Metals and alloys Metals have high melting points and conduct because delocalised electrons can move. They are malleable because layers of ions can slide. Alloys contain atoms of different sizes that distort the layers, making it harder for them to slide, so alloys are harder.
• Classifying structures Use data: high melting point and conducts when solid suggests metallic or graphite; high melting point and conducts only when molten or dissolved suggests ionic; low melting point and does not conduct suggests molecular covalent.

Common mistakes in 1.3 Structures

• Saying covalent bonds break when a molecular substance melts. Only the weak forces between molecules are overcome.
• Explaining that ionic compounds conduct when solid because they contain ions. The ions are fixed in place in the solid and can only move when molten or dissolved.
• Saying graphite conducts because it has free ions. It has delocalised electrons.
• Stating that diamond has delocalised electrons. All four outer electrons of each carbon are used in bonding.
• Writing that alloys are stronger because they are mixtures. Explain that different-sized atoms disrupt the layers so they cannot slide easily.

Try three 1.3 Structures exam-style questions