Types of Substance

    OCR
    GCSE

    Substances are categorized into four primary structural types: giant ionic, simple molecular, giant covalent, and metallic, determined by the nature of the constituent particles and the bonding forces between them. Candidates must distinguish between strong primary bonds (ionic, covalent, metallic) and weak intermolecular forces to explain physical properties such as melting point, solubility, and electrical conductivity. This topic underpins the understanding of material science, requiring the application of bonding theories to predict the behavior of unfamiliar compounds.

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    Objectives
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    Exam Tips
    4
    Pitfalls
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    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award marks for stating that ionic compounds conduct electricity only when molten or in solution due to mobile ions
    • Credit responses that identify weak intermolecular forces between molecules in simple covalent substances, not weak covalent bonds
    • Award marks for describing metallic bonding as a lattice of positive ions in a 'sea' of delocalised electrons
    • Credit the explanation that giant covalent structures (diamond, silicon dioxide) have high melting points because many strong covalent bonds must be broken
    • Award marks for linking the conductivity of graphite specifically to delocalised electrons moving between layers

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You identified the substance correctly, but you must reference the specific particles (ions/electrons) responsible for conductivity"
    • "Be careful not to say 'covalent bonds are broken' when melting water/methane — focus on the forces *between* the molecules"
    • "Excellent use of 'delocalised electrons' — now explain exactly how this feature leads to thermal conductivity"
    • "To secure the top band, explicitly compare the energy requirements: why does breaking a lattice take more energy than overcoming intermolecular forces?"

    Marking Points

    Key points examiners look for in your answers

    • Award marks for stating that ionic compounds conduct electricity only when molten or in solution due to mobile ions
    • Credit responses that identify weak intermolecular forces between molecules in simple covalent substances, not weak covalent bonds
    • Award marks for describing metallic bonding as a lattice of positive ions in a 'sea' of delocalised electrons
    • Credit the explanation that giant covalent structures (diamond, silicon dioxide) have high melting points because many strong covalent bonds must be broken
    • Award marks for linking the conductivity of graphite specifically to delocalised electrons moving between layers

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When given a table of data (MP, BP, Conductivity), classify the substance *before* answering the specific questions to ensure consistency
    • 💡Never use the phrase 'weak bonds' for simple molecules; always specify 'weak intermolecular forces'
    • 💡For 6-mark Level of Response questions comparing diamond and graphite, structure your answer into: Bonding (similarities), Structure (differences), and Properties (resulting implications)
    • 💡Memorise the specific phrase 'electrostatic attraction between oppositely charged ions' for ionic bonding definitions

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Stating that covalent bonds break when simple molecular substances melt (it is the intermolecular forces that break)
    • Describing ionic lattices as containing 'molecules' or referring to intermolecular forces in ionic compounds
    • Claiming ionic compounds conduct electricity in the solid state
    • Confusing the term 'delocalised electrons' with 'free ions' when discussing metals or graphite

    Key Terminology

    Essential terms to know

    Giant Ionic Lattices
    Simple Molecular (Covalent) Structures
    Giant Covalent (Macromolecular) Structures
    Metallic Bonding and Alloys
    Structure-Property Relationships

    Likely Command Words

    How questions on this topic are typically asked

    Explain
    Compare
    Deduce
    Describe
    Predict
    Evaluate

    Practical Links

    Related required practicals

    • •{"code":"PAG 2","title":"Testing conductivity of solids and solutions","relevance":"Distinguishing between ionic and covalent substances based on electrical conductivity"}

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