OxfordAQA International GCSE Chemistry 3.2 Structure, Bonding and the Properties of Matter Exam Questions

About OxfordAQA International GCSE Chemistry 3.2 Structure, Bonding and the Properties of Matter

Structure and bonding explains why substances behave as they do, and it is one of the most heavily examined ideas in OxfordAQA International GCSE Chemistry. You need to describe ionic bonding by electron transfer, covalent bonding by shared pairs and metallic bonding with delocalised electrons, and draw dot and cross diagrams. You then link each structure to melting point and electrical conductivity, and study diamond, graphite and fullerenes. Nanoparticles appear in the separate Chemistry course only. The topic uses electronic structure from 3.1 and supports electrolysis, metals and organic chemistry. Examiners reward answers that name the particles and forces involved rather than just saying bonds are strong.

What you need to know

• Ionic bonding Metal atoms lose outer electrons to form positive ions and non-metal atoms gain electrons to form negative ions, both with noble gas arrangements. Group 1 forms 1+ ions and Group 7 forms 1- ions. Ionic compounds are giant lattices held by strong electrostatic attraction in all directions; you need the sodium chloride structure.
• Covalent bonding A covalent bond is a shared pair of electrons. Draw dot and cross diagrams for H2, Cl2, O2, N2, HCl, H2O, NH3 and CH4. Diamond and silicon dioxide are giant covalent structures.
• Metallic bonding Metals are giant structures of positive ions in a regular pattern with delocalised outer electrons; the attraction between the ions and the electrons holds the structure together.
• Properties of ionic compounds High melting and boiling points because many strong electrostatic forces must be overcome. They conduct electricity when molten or dissolved because ions are free to move, but not as solids.
• Simple molecules Low melting and boiling points because only weak intermolecular forces are overcome, not the covalent bonds. They do not conduct because the molecules have no overall charge.
• Carbon structures In diamond each carbon forms four covalent bonds, so it is very hard with a very high melting point. In graphite each carbon bonds to three others in layers with weak forces between them, so layers slide; one delocalised electron per atom lets graphite conduct. Fullerenes are based on hexagonal rings and are used in drug delivery, lubricants, catalysts and nanotubes.
• Nanoparticles (separate Chemistry) Nanoparticles are 1 to 100 nm in size and have a very high surface area to volume ratio, so they can have different properties from the same material in bulk.

Common mistakes in 3.2 Structure, Bonding and the Properties of Matter

• Saying ionic compounds have strong covalent bonds or intermolecular forces. Ionic compounds have strong electrostatic forces between oppositely charged ions.
• Saying covalent bonds break when a simple molecular substance boils. Only the weak intermolecular forces are overcome.
• Saying solid ionic compounds conduct because they contain ions. The ions are fixed in the lattice and can only move when molten or dissolved.
• Saying graphite conducts because of free ions. It conducts because of delocalised electrons.
• Saying electrons move in metals because they are loose. Use the word delocalised and say they can move through the whole structure.

Try three 3.2 Structure, Bonding and the Properties of Matter exam-style questions