Edexcel A Level Chemistry Topic 2: Bonding and Structure Exam Questions

About Edexcel A Level Chemistry Topic 2: Bonding and Structure

Topic 2 of Edexcel A Level Chemistry explains how bonding determines structure and properties. You study ionic bonding and evidence for ions from electrolysis, covalent and dative covalent bonding, and the shapes of molecules and ions using electron-pair repulsion theory. Electronegativity and bond polarity lead into intermolecular forces: London forces, permanent dipole-dipole forces and hydrogen bonds, used to explain boiling temperatures and solubility. The topic also covers metallic bonding and the structures of giant lattices, including graphite, diamond and graphene. It is examined in both Paper 1 and Paper 2 as well as Paper 3. Examiners often test shapes with bond angles and explanations of physical properties.

What you need to know

• Ionic bonding Strong electrostatic attraction between oppositely charged ions. Ionic radius depends on charge and number of electrons, and the migration of coloured ions in electrolysis is evidence for ions.
• Covalent and dative bonding A covalent bond is the strong electrostatic attraction between two nuclei and a shared pair of electrons. In a dative covalent bond both electrons come from one atom, as in NH4+.
• Shapes of molecules Electron pairs repel to minimise repulsion, and lone pairs repel more than bonding pairs. Know linear, trigonal planar, tetrahedral, pyramidal, non-linear, trigonal bipyramidal and octahedral shapes with their bond angles.
• Electronegativity and polarity Electronegativity is the ability of an atom to attract the bonding electrons in a covalent bond. A molecule with polar bonds can be non-polar overall if it is symmetrical, as in CO2 and CCl4.
• Intermolecular forces London forces arise from instantaneous and induced dipoles and increase with the number of electrons. Permanent dipole forces act between polar molecules. Hydrogen bonds form between H bonded to N, O or F and a lone pair on N, O or F.
• Effects on properties Branched alkanes have lower boiling temperatures than straight-chain isomers because of fewer points of contact. Ice is less dense than water due to its open hydrogen-bonded lattice.
• Giant structures Metallic bonding is attraction between metal ions and delocalised electrons. Diamond, graphite and graphene are giant covalent; graphite and graphene conduct because of delocalised electrons.

Common mistakes in Topic 2: Bonding and Structure

• Using the term van der Waals when the Edexcel mark scheme expects London forces for induced dipole attractions.
• Saying covalent bonds break when a simple molecular substance boils; only intermolecular forces are overcome.
• Drawing hydrogen bonds without the lone pair or with a bond angle far from 180 degrees around the H.
• Giving the shape of a molecule without considering lone pairs, for example calling H2O linear.
• Explaining the solubility of ionic compounds without mentioning hydration of ions by polar water molecules.

Try three Topic 2: Bonding and Structure exam-style questions