AQA GCSE Chemistry 4.2.1 Chemical Bonds: Ionic, Covalent and Metallic Exam Questions

About AQA GCSE Chemistry 4.2.1 Chemical Bonds: Ionic, Covalent and Metallic

AQA GCSE Chemistry 4.2.1 explains the three types of strong chemical bond: ionic, covalent and metallic. You learn how electrons are transferred or shared, how to draw dot and cross diagrams, how ionic lattices form, how to work out formulae and how metallic bonding works. It is part of section 4.2 and is examined on Paper 1, building on electronic structure from 4.1 and leading into the properties of substances in 4.2.2. Examiners often ask for dot and cross diagrams for compounds such as magnesium oxide or methane, ask you to deduce a formula from a diagram, and ask you to evaluate the limitations of different bonding models.

What you need to know

• Ionic bonding Ionic bonding happens between a metal and a non-metal. Metal atoms lose electrons to form positive ions and non-metal atoms gain electrons to form negative ions, giving each ion the electronic structure of a noble gas.
• Dot and cross diagrams Show the electrons transferred and the charge on each ion, for example Na+ and Cl- with full outer shells in square brackets. Group 1 ions are 1+, Group 2 are 2+, Group 6 are 2- and Group 7 are 1-.
• Ionic compounds An ionic compound is a giant structure of ions held by strong electrostatic forces of attraction between oppositely charged ions in all directions. You should be able to work out the empirical formula from a diagram of the lattice, for example NaCl or MgCl2.
• Covalent bonding A covalent bond is a shared pair of electrons between non-metal atoms. Covalently bonded substances can be small molecules (H2, Cl2, O2, N2, HCl, H2O, NH3, CH4), large molecules such as polymers, or giant covalent structures such as diamond and silicon dioxide.
• Metallic bonding Metals are giant structures of positive ions arranged in a regular pattern with delocalised electrons. Metallic bonding is the strong electrostatic attraction between the positive ions and the sea of delocalised electrons.
• Limitations of models Dot and cross diagrams do not show the 3D shape or relative sizes; ball and stick models show bonds as sticks that do not exist; 2D diagrams cannot show the arrangement in space.

Common mistakes in 4.2.1 Chemical Bonds: Ionic, Covalent and Metallic

• Showing electrons being shared in an ionic compound. In ionic bonding electrons are transferred; only covalent bonds involve sharing.
• Forgetting the square brackets and charges on ions in dot and cross diagrams, or drawing extra electrons around the metal ion's empty outer shell.
• Describing metallic bonding as attraction between atoms. It is attraction between positive metal ions and delocalised electrons.
• Saying ionic bonds are between 'molecules'. Ionic compounds are giant lattices of ions, not molecules.
• Drawing double bonds incorrectly, for example showing O2 with a single shared pair. Oxygen needs two shared pairs (a double bond).

Try three 4.2.1 Chemical Bonds: Ionic, Covalent and Metallic exam-style questions