Comparing Bonding Types and Properties

This final lesson brings together everything you have learned about ionic, simple covalent (molecular), giant covalent and metallic bonding. Being able to compare these four types, interpret experimental data and identify an unknown substance from its properties is a key skill for the Edexcel GCSE Chemistry (1CH0) exam.

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The Four Main Types of Bonding and Structure

1. Ionic Compounds (Giant Ionic Lattice)

• Bonding: electrostatic attraction between oppositely charged ions (metal + non-metal).
• Structure: giant ionic lattice — regular 3D arrangement of ions.
• Melting/boiling point: HIGH — strong forces in all directions.
• Electrical conductivity (solid): NO — ions in fixed positions.
• Electrical conductivity (molten/dissolved): YES — ions free to move.
• Solubility in water: Many are soluble.
• Example: NaCl, MgO, KBr.

2. Simple Molecular Substances (Simple Covalent)

• Bonding: strong covalent bonds within molecules; weak intermolecular forces between molecules.
• Structure: small, discrete molecules.
• Melting/boiling point: LOW — weak intermolecular forces, little energy to overcome.
• Electrical conductivity: NO (in any state) — no free electrons or ions.
• Solubility in water: Variable (some dissolve, many don't).
• Example: H₂O, CO₂, CH₄, O₂.

3. Giant Covalent Structures

• Bonding: strong covalent bonds throughout the entire structure.
• Structure: giant lattice of atoms — no individual molecules.
• Melting/boiling point: VERY HIGH — many strong covalent bonds to break.
• Electrical conductivity: Usually NO (except graphite — delocalised electrons).
• Solubility in water: Insoluble.
• Example: diamond, graphite, silicon dioxide.

4. Metallic Structures

• Bonding: electrostatic attraction between positive metal ions and delocalised electrons.
• Structure: regular lattice of positive ions in a sea of electrons.
• Melting/boiling point: Generally HIGH (varies — Na is low, Fe is high).
• Electrical conductivity (solid): YES — delocalised electrons free to move.
• Electrical conductivity (molten): YES.
• Malleable/ductile: YES — layers slide, electrons re-adjust.
• Example: Fe, Cu, Al, Na.

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Master Comparison Table

Property	Ionic	Simple Molecular	Giant Covalent	Metallic
Type of particles	Ions	Molecules	Atoms	Positive ions + delocalised electrons
Type of bonding	Ionic (electrostatic, ion–ion)	Covalent within molecules, weak forces between	Covalent throughout	Metallic (ion–electron)
Melting point	High	Low	Very high	Generally high
Boiling point	High	Low	Very high	Generally high
Conduct electricity (solid)	No	No	No (except graphite)	Yes
Conduct electricity (liquid/molten)	Yes	No	N/A (very hard to melt)	Yes
Conduct electricity (dissolved)	Yes (if soluble)	No	N/A (insoluble)	N/A
Soluble in water	Many are	Variable	No	No
Malleable/ductile	No (brittle)	N/A (often gas/liquid)	No (hard/brittle)	Yes
Hardness	Hard but brittle	Soft (if solid)	Very hard	Variable

Exam Tip: This table is extremely useful for revision. Many exam questions give you a set of properties and ask you to identify the bonding type. Use this table to work through the clues systematically.

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How to Identify the Bonding Type from Properties

When given data about an unknown substance, work through these questions:

flowchart TD
    A["Start: Unknown substance"] --> B{"Does it conduct\nelectricity as a solid?"}
    B -->|Yes| C["METALLIC\n(delocalised electrons)"]
    B -->|No| D{"Does it have a\nhigh melting point?"}
    D -->|"No (low mp)"| E["SIMPLE MOLECULAR\n(weak intermolecular forces)"]
    D -->|"Yes (high mp)"| F{"Does it conduct when\nmolten or dissolved?"}
    F -->|Yes| G["IONIC\n(mobile ions when molten/dissolved)"]
    F -->|No| H["GIANT COVALENT\n(strong covalent bonds,\nno mobile charges)"]

Step-by-Step Guide

1. Does it conduct electricity as a solid?

   • Yes → likely metallic (delocalised electrons in solid).
   • No → move to step 2.

2. Does it have a high or low melting point?

   • Low melting point → likely simple molecular (weak intermolecular forces).
   • High melting point → either ionic or giant covalent — move to step 3.

3. Does it conduct electricity when molten or dissolved in water?

   • Yes → ionic (ions become free to move when molten/dissolved).
   • No → giant covalent (no free electrons or ions in any state — unless it's graphite).

Exam Tip: The exception to watch for is graphite — it has a very high melting point AND conducts electricity as a solid. If you see a substance with a very high mp that conducts as a solid, it could be graphite (or a metal — check other properties).

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Practice: Interpreting Experimental Data

Example 1

Property	Substance X
Melting point	1610 °C
Conducts as solid	No
Conducts when molten	No
Soluble in water	No

Analysis:

• Very high melting point → not simple molecular.
• Does not conduct as solid → not metallic.
• Does not conduct when molten → not ionic (ionic would conduct when molten).
• Answer: Giant covalent structure (e.g. silicon dioxide).

Example 2

Property	Substance Y
Melting point	770 °C
Conducts as solid	No
Conducts when molten	Yes
Soluble in water	Yes

Analysis:

• High melting point → not simple molecular.
• Does not conduct as solid → not metallic.
• Conducts when molten → ionic (ions free to move in liquid state).
• Soluble in water → consistent with ionic.
• Answer: Ionic compound (e.g. calcium chloride).

Example 3

Property	Substance Z
Melting point	-161 °C
Conducts as solid	No
Conducts as liquid	No
Soluble in water	No

Analysis:

• Very low melting point → weak intermolecular forces.
• Does not conduct in any state → no ions or free electrons.
• Answer: Simple molecular substance (e.g. methane).

Example 4

Property	Substance W
Melting point	1085 °C
Conducts as solid	Yes
Malleable	Yes
Ductile	Yes

Analysis:

• High melting point.
• Conducts as solid → has mobile charge carriers (delocalised electrons).
• Malleable and ductile → layers can slide.
• Answer: Metal (e.g. copper).

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Common Exam Mistakes and How to Avoid Them

Common Mistake	Correction
"Ionic bonds break when it melts"	The giant ionic lattice breaks apart — the electrostatic forces between ions are overcome
"Covalent bonds break when water boils"	The intermolecular forces between molecules are overcome — the covalent bonds within molecules do not break
"Graphite conducts because ions move"	Graphite has no ions — it conducts because of delocalised electrons
"Diamond is hard because it has strong bonds"	Be specific: diamond is hard because each carbon is bonded to 4 others in a rigid tetrahedral arrangement with strong covalent bonds
"Metals conduct because electrons are free"	Be precise: delocalised electrons are free to move through the structure and carry charge
"Ionic compounds always conduct"	Only when molten or dissolved — NOT as solids (ions in fixed positions)
"All giant covalent structures don't conduct"	Graphite does conduct — it has delocalised electrons

Exam Tip: In 6-mark questions, marks are awarded for precise scientific language. Always name the specific type of force or bond, and explain why a property exists — don't just state it.

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Summary: Quick-Reference Table

	Ionic	Simple Molecular	Giant Covalent	Metallic
Particles	Ions	Molecules	Atoms	Metal ions + e⁻
MP / BP	High	Low	Very high	High
Conduct (solid)	No	No	No*	Yes
Conduct (liquid)	Yes	No	N/A	Yes
Malleable	No	N/A	No	Yes
Soluble (water)	Often	Variable	No	No

* Except graphite

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Key Points

• There are four main types of bonding/structure: ionic, simple molecular, giant covalent and metallic.
• Each type has characteristic properties related to its structure and bonding.
• To identify the bonding type: check melting point, electrical conductivity (solid vs molten), solubility and malleability.
• Always use precise scientific language — name the specific forces and explain the mechanism.
• Watch out for common exceptions: graphite conducts, water has a higher bp than expected.
• Practice interpreting data tables — this is a very common exam question type.

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Practice Questions

1. A substance has a melting point of 2072 °C, does not conduct electricity as a solid, and does not conduct when molten. What type of structure does it have? Explain your reasoning.
2. Explain why sodium chloride conducts electricity when dissolved in water but not as a solid.
3. Compare the structures of diamond and sodium chloride. Explain why both have high melting points.
4. A substance melts at -114 °C and does not conduct electricity in any state. Identify the type of bonding and structure, and justify your answer.
5. Draw a flowchart to show how you would identify whether an unknown substance is ionic, simple molecular, giant covalent or metallic.
6. Explain why copper is malleable but sodium chloride is brittle, even though both have high melting points.

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