Chemical bonds — AQA GCSE Chemistry
Test yourself on Chemical bonds with AQA GCSE practice questions.
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Chemical bonds explained
Covalent bonding occurs between non-metal atoms that share pairs of electrons to achieve stable electron arrangements.
Read the full explanation
Each shared pair is attracted to both nuclei, holding the atoms together. For example, in H₂ each hydrogen atom contributes one electron to a shared pair, and in H₂O oxygen shares two pairs, one with each hydrogen. Metallic bonding occurs in metals, where positive metal ions are surrounded by a sea of delocalised electrons. The particles in metallic bonding are often described as positive ions, but the specification phrase 'atoms which share delocalised electrons' emphasises that the outer electrons are not attached to any single atom. You should be able to contrast the two: covalent bonding involves localised shared pairs between specific atoms, while metallic bonding involves delocalised electrons shared across the whole structure.
Your focus
- Describe covalent bonding as sharing pairs of electrons.
- Describe metallic bonding as sharing delocalised electrons.
- Compare the particles and electron behaviour in covalent and metallic bonding.
Chemical bonds exam tips
Marking Points
- States that covalent bonding involves atoms sharing pairs of electrons.
- Gives an example such as H₂, Cl₂, O₂, H₂O or CH₄ with the correct number of shared pairs.
- States that metallic bonding involves delocalised electrons shared between atoms or positive ions.
- Explains that delocalised electrons are free to move throughout the metal structure.
- Contrasts covalent and metallic bonding in terms of localised versus delocalised electrons.
Examiner Tips
- 💡Use dot-and-cross diagrams to show shared pairs clearly, especially for simple molecules.
- 💡For metallic bonding, describe the structure as positive ions in a sea of delocalised electrons.
- 💡When comparing, use the words 'localised' for covalent shared pairs and 'delocalised' for metallic electrons.
Common Mistakes
- Saying covalent bonding involves transfer of electrons. Correction: covalent bonding involves sharing pairs of electrons.
- Describing metallic bonding as covalent sharing between specific pairs. Correction: metallic bonding involves delocalised electrons shared across the whole lattice.
- Writing formulas with baseline indices, for example writing the hydrogen count inline. Correction: use subscripts such as H₂, O₂ and CH₄.