Bonding, Structure and Properties Overview

This lesson provides a comprehensive overview of all the bonding, structure, and properties content required for the AQA GCSE Chemistry specification (4.2.1-4.2.4). It brings together ionic, covalent, and metallic bonding, linking structure to properties in a way that prepares you for comparison questions and extended-response tasks in the exam.

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The Three Types of Bonding

There are three main types of chemical bonding. The type of bonding that occurs depends on which types of atoms are involved.

Bonding Type	Occurs Between	What Happens	Particles Formed
Ionic	Metal + non-metal	Electrons are transferred from metal to non-metal	Positive and negative ions
Covalent	Non-metal + non-metal	Electrons are shared between atoms	Molecules (or giant covalent networks)
Metallic	Metal + metal	Outer electrons are delocalised	Metal ions + sea of electrons

Exam Tip: If the exam asks "what type of bonding is present in...?" look at the elements involved. Metal + non-metal = ionic. Non-metal + non-metal = covalent. Metal only = metallic. There are exceptions (e.g. ammonium compounds are ionic despite containing non-metals), but this rule works for the vast majority of GCSE questions.

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The Four Types of Structure

Substances can be classified into four main types of structure:

1. Giant Ionic Lattice

• Made of positive and negative ions.
• Held together by strong electrostatic forces in all directions.
• Examples: NaCl, MgO, CaCl2.

2. Simple Molecular (Simple Covalent)

• Made of small molecules with strong covalent bonds within molecules and weak intermolecular forces between molecules.
• Examples: H2O, CO2, CH4, O2.

3. Giant Covalent

• A large network of atoms connected by strong covalent bonds in all directions.
• No molecules — the whole structure is one giant molecule.
• Examples: diamond, graphite, graphene, silicon dioxide.

4. Giant Metallic Lattice

• Regular arrangement of metal ions surrounded by a sea of delocalised electrons.
• Held together by strong metallic bonds.
• Examples: iron, copper, aluminium, gold.

graph TD
    A["Types of Structure"] --> B["Giant Ionic<br/>e.g. NaCl, MgO"]
    A --> C["Simple Molecular<br/>e.g. H2O, CO2"]
    A --> D["Giant Covalent<br/>e.g. Diamond, Graphite"]
    A --> E["Giant Metallic<br/>e.g. Iron, Copper"]
    B --> F["High MP, conducts<br/>when molten/dissolved"]
    C --> G["Low MP, does not<br/>conduct electricity"]
    D --> H["Very high MP,<br/>hard, most do not conduct"]
    E --> I["High MP, conducts,<br/>malleable, ductile"]

    style A fill:#2c3e50,color:#fff
    style B fill:#e74c3c,color:#fff
    style C fill:#3498db,color:#fff
    style D fill:#27ae60,color:#fff
    style E fill:#f39c12,color:#fff

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Linking Structure to Properties

This is the most important skill for the exam: being able to explain why a substance has certain properties based on its structure and bonding.

Melting and Boiling Points

Structure Type	Typical Melting Point	Explanation
Simple molecular	Low	Only weak intermolecular forces need to be overcome (covalent bonds do NOT break).
Giant ionic	High	Strong electrostatic forces between oppositely charged ions in all directions must be overcome.
Giant covalent	Very high	Many strong covalent bonds throughout the structure must be broken.
Giant metallic	High (varies)	Strong attraction between metal ions and delocalised electrons must be overcome.

Electrical Conductivity

Structure Type	Conducts?	Explanation
Simple molecular	No	No charged particles free to move.
Giant ionic (solid)	No	Ions are in fixed positions.
Giant ionic (molten/dissolved)	Yes	Ions are free to move and carry charge.
Giant covalent (most)	No	No charged particles free to move (all electrons in covalent bonds).
Graphite / Graphene	Yes	Delocalised electrons are free to move and carry charge.
Giant metallic	Yes	Delocalised electrons are free to move and carry charge.

Exam Tip: The ability to explain electrical conductivity is tested almost every year. Remember: for a substance to conduct electricity, it must contain charged particles that are free to move. Metals and graphite have delocalised electrons. Molten/dissolved ionic compounds have mobile ions. Everything else does not conduct.

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How to Identify Structure Type from Properties

If the exam gives you data and asks you to identify the type of structure, use this decision-making process:

Step 1: Check the Melting Point

• Low melting point (below about 300 degrees C) → probably simple molecular.
• High melting point (above about 500 degrees C) → giant structure (ionic, covalent, or metallic).

Step 2: Check Electrical Conductivity

• Conducts when solid → metallic (delocalised electrons).
• Conducts when molten but not when solid → giant ionic (ions free to move when melted).
• Does not conduct at all → giant covalent (like diamond or SiO2) or simple molecular.
• Exception: graphite is giant covalent but conducts (delocalised electrons).

Step 3: Check Other Properties

• Brittle → ionic.
• Malleable / ductile → metallic.
• Very hard → giant covalent.
• Soft / low melting point → simple molecular.

Clue	Structure Type
Low MP, does not conduct	Simple molecular
High MP, conducts when molten, brittle	Giant ionic
Very high MP, very hard, does not conduct	Giant covalent (diamond, SiO2)
Very high MP, conducts, soft/slippery	Giant covalent (graphite)
High MP, conducts when solid, malleable	Metallic

Exam Tip: In the exam, you may be given a table of melting points and conductivity data for unknown substances and asked to identify the structure type. Work through the decision process systematically: melting point first, then conductivity, then other properties. This approach will give you the correct answer every time.

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Bonding Diagrams Summary

You need to be able to draw the following types of diagrams: